Metrosensor: electrodes from Metrohm
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  • 1. Metrosensor electrodesPrecision is not accidental, but brought about bydesign!
  • 2. 2
  • 3. Table of contentsWhich electrode for which application?Electrode recommendations for pH measurement 6-7 6 How is a Metrosensor made? 78-79 3Electrode recommendations for titration 7 Theoretical fundamentals 80-101 1. Fundamentals of potentiometry 80-Electrode catalog 8-69 1.1. Measuring setup 80iTrodes 8-9 1.2. From potential to ion concentration –Separate pH electrodes 12-13 the Nernst equation 80-81Electrodes for pH measurement 14-17 1.3. Measuring electrodes 82Electrodes for pH titration 18-21 1.3.1. pH glass electrodes 82-86Special electrodes for pH measurement/pH titration 22-25 1.3.2. Metal electrodes 86-88Separate metal and carbon electrodes 28-29 1.3.3. Ion-selective electrodes 88-90Titrodes 30-31 1.4. Reference electrodes 90Combined metal electrodes 32-33 1.4.1. Silver/silver chloride reference system 90Electrodes for voltammetry 34-37 1.4.2. Metrosensor «Long Life» reference system 91Electrodes for Karl Fischer titration 38-41 1.4.3. Diaphragms 91-94Ion-selective electrodes and accessories 44-47 1.4.4. Reference electrolytes andSurfactant electrodes and accessories 48-51 bridge electrolytes 95Reference electrodes 54-57 2. Fundamentals of conductometry 96-100Conductometric measuring cells 60-65 2.1. General 96-99Temperature sensors 66-67 2.2. Conductivity measurement in accordanceSensors for photometry 68-69 with USP and Pharm. Europe (EP) 99-100 3. Temperature measurement 101Accessories 71-77Electrode components and other accessories 72-73 Appendix 102-106Ion standards, buffer solutions, electrolytes 74-75 Technical specifications 102-106Electrical connections 76-77
  • 4. 4 Metrohm stands for 65 year’s experience in ion analysis – why should you wrack your brains, when weve already done the thinking for you? Metrohm Application Bulletins – instructions that are guaranteed to work. Pharm PAC – the most important methods for the Metrohm PACs (Potentiometric Analysis Collections) determination of pharmaceutical ingredients in contain ready-to-use methods, which are right up to accordance with European and US pharmacopeias. date and always in compliance with the respective stand- ards and regulations. Wine PAC – the most important methods in wine analysis. Surf PAC – the most important methods in sur- factant analysis. Plate PAC – the most important methods for the analysis of galvanic baths. Oil PAC – the most important methods for the analysis of petroleum products. Food PAC – the most important methods in food analysis. Get your know-how from the market leader! www.metrohm.com
  • 5. Electrode catalogThe illustrations of the articles are, unless specified other-wise, approximately in original size. Materials abbreviations: EP Epoxide 5 PCTFE PolychlortrifluoroethyleneUnless otherwise specified, all combined pH electrodes PE Polyethyleneare filled with the referenced electrolytes c(KCl) = 3 mol/L PEEK Polyetheretherketone(Order number 6.2308.020). PMMA Polymethyl metacrylate POM PolyoxymethyleneThe abbreviation «LL reference system» stands for the PP PolypropyleneMetrosensor «Long Life» reference system. More detailed PTFE Polytetrafluoroethyleneinformation on this can be found in the theoretical PVC Polyvinyl chloridesection, Chapter 1.4.2.«DJ» stands for «double junction». These electrodes areequipped with a bridge electrolyte chamber; the bridgeelectrolyte is replaceable, which means that it can beadapted to suit the sample.Detailed information concerning technical specificationscan be found in the appendix «Technical Specifications.»The electrochemical parameters are specified for 25 °C,the outflow rates with a hydrostatic pressure of a 10 cmhigh water column. «Shaft length» refers to the length ofthe electrode tip up to the lower edge of the electrodeplug-in head. The installation length is the length fromthe electrode tip to the upper edge of the standardground joint. In the case of flexible SGJ sleeves, this cor-responds to the length down to the electrolyte refillopening below. All flexible SGJ sleeves have like their sizethe standard ground joint 14/15.
  • 6. Electrodes for pH measurement6 Application Universal Details Clear, aqueous solutions, pH 0...14 Electrode Primatrode with NTC Order number 6.0228.010 Page 14 Universal laboratory use, pH 0...14 Unitrode with Pt 1000 6.0258.600 16 Routine measurement in similar samples Ecotrode Gel with NTC 6.0221.600 14 pH 1...11 Water General (demineralized water, drinking Aquatrode Plus with Pt 1000 6.0257.000 16 water, process water, sea water, environ- mental sector) Waste water General Unitrode with Pt 1000 6.0258.600 16 Sewage containing sulfides Profitrode 6.0255.100 18 Soil samples General (aqueous suspensions) Flat-membrane pH electrode 6.0256.100 22 Agriculture Fertilizers Unitrode with Pt 1000 6.0258.600 16 Horticulture solutions containing proteins Porotrode 6.0235.200 22 Plant cultivation Liquid manure Profitrode 6.0255.100 18 Small sample volumes, culture media Biotrode 6.0224.100 22 Nutrient solutions Viscotrode 6.0239.100 24 Food General Unitrode with Pt 1000 6.0258.600 16 Beverages Food containing proteins, beer Porotrode 6.0235.200 22 Semi-luxury arti- Bread, meat, cheese, dough (measurements Spearhead electrode 6.0226.100 22 cles semi-solid samples) Fruit and vegetable juices, wine, spirits Unitrode with Pt 1000 6.0258.600 16 Drinking water Aquatrode Plus with Pt 1000 6.0257.000 16 Pharmaceuticals Creams, liquid formulations, medicinal syrup, Viscotrode 6.0239.100 24 Biological mouthwash solutions, raw materials monitor- samples ing in accordance with pharmacopoeias Dialysis solutions, urine Unitrode with Pt 1000 6.0258.600 16 Solutions containing proteins Porotrode 6.0235.200 22 Infusion solutions Aquatrode Plus with Pt 1000 6.0257.000 16 Small sample volumes, gastric juice, serum Biotrode 6.0224.100 22 Pilot plant measurements Syntrode with Pt 1000 6.0248.0X0 24 Cosmetics General (emulsions, shampoos, shower Viscotrode 6.0239.100 24 baths, liquid soaps, lotions, mouthwashes, perfumes) Skin (surfaces) Flat-membrane pH electrode 6.0256.100 22 Make-up Microelectrode 6.0234.100 24 Cleaning agents General (detergents, dishwashing liquids, Viscotrode 6.0239.100 24 Detergents cleaning agents, surfactant solutions) Samples with pH values > 10 Profitrode 6.0255.100 18 High-viscosity samples Unitrode with Pt 1000 6.0258.600 16 Leather Bleaching and dyeing baths, tanning liquors Profitrode 6.0255.100 18 Paper Fountain solution for offset printing, glue Unitrode with Pt 1000 6.0258.600 16 Textiles Leather, paper, textiles (surface) Flat-membrane pH electrode 6.0256.100 22 Washing liquors Viscotrode 6.0239.100 24 Paints Stains (wood), dye baths, inks Profitrode 6.0255.100 18 Lacquers Dispersions, emulsions, resins, lacquers, Unitrode with Pt 1000 6.0258.600 16 Solvents suspensions Paint coatings (surfaces) Flat-membrane pH electrode 6.0256.100 22 Non-aqueous, polar solvents EtOH-Trode 6.0269.100 16 Electroplating General (etching, pickling and degreasing baths, Profitrode 6.0255.100 18 Metal process- alkaline electroplating and phosphatizing ing Acidic electroplating baths Unitrode with Pt 1000 6.0258.600 16 Drilling oil emulsions Viscotrode 6.0239.100 24 Special Measurements in semi-solid samples Spearhead electrode 6.0226.100 22 applications Solutions containing proteins Porotrode 6.0235.200 22 Samples with pH values > 12 and tempera- Unitrode with Pt 1000 6.0258.600 16 tures 50...80 °C Temperature 80...100 °C Unitrode with Pt 1000 reference 6.0258.600 16 electrolyte: Idrolyte Ion-deficient, weakly buffered solutions Aquatrode Plus with Pt 1000 6.0257.000 16 Small sample volumes Biotrode 6.0224.100 22 Flat-membrane pH electrode 6.0256.100 22 Surface measurements Flat-membrane pH electrode 6.0256.100 22 Developer baths, concentrated acids Profitrode 6.0255.100 18 Emulsions/suspensions Unitrode with Pt 1000 6.0258.600 16 Fuels containing ethanol/E85 EtOH-Trode 6.0269.100 16
  • 7. Electrodes for titrationApplicationAqueous Details General Electrode Ecotrode Plus Order number 6.0262.100 Page 18 7acid/base Routine measurement in similar samples Ecotrode Gel 6.0221.100 18titrations Alkaline samples, Bayer liquors Unitrode 6.0259.100 18 Titrations at high temperatures Unitrode with reference electro- 6.0259.100 18 lyte Idrolyte Acid content of alcoholic beverages Unitrode with Pt 1000 6.0258.600 18 Titrations with small sample volumes Microelectrode 6.0234.100 24 Flat-membrane electrode 6.0256.100 22 Titrations in ion-deficient aqueous media Aquatrode Plus 6.0253.100 20 Carbonate hardness and acid capacity of Aquatrode Plus with Pt 1000 6.0257.000 16 water, p & m values Electroplating, etching and phosphatizing Profitrode 6.0255.100 18 Etching baths containing fluoride or Combined antimony electrode 6.0421.100 32 hydrofluoric acid Samples containing protein Porotrode 6.0235.200 22Non-aqueous Titrations with perchloric acid, cyclohexylamine, Solvotrode with c(LiCl) = 2 mol/L 6.0229.100 20acid/base alcoholic HCl, determination of base number in ethanoltitrations (TBN) of crude oil products Titrations with alcoholic KOH, NaOH and Solvotrode with c(TEABr) = 0.4 6.0229.100 20 TBAOH, potassium methylate, determination mol/L in ethylene glycol of the total acid number (TAN) of petroleum products, free fatty acid/hydroxyl number in oils and fatsRedox titrations Titrations without change of the pH value Pt Titrode 6.0431.100 30Titrants: Titrations with change of the pH value Combined LL-Pt ring electrode 6.0451.100 32arsenite, cersulfate Chemical oxygen demand (COD) in waters Combined LL-Au ring electrode 6.0452.100 32iron(III), iodine,potassium bromate Penicillin, ampicillin Combined LL-Au ring electrode 6.0452.100 32sodium nitrite Bromatometry, iodometry and cerimetry in Pt Titrode 6.0431.100 30oxalic acid, perman- accordance with Pharm. Europe & USPganate, thiosul-fate, titanium(III),Hg(NO3)2Karl Fischer rea- Water determination according to Karl Double Pt wire electrode 6.0338.100 38gent FischerTitrations in Double Pt wire electrode 6.0341.100 38«Ipol» modePrecipitation Chloride in general, sodium chloride content Ag Titrode 6.0430.100 30titrations in foodsTitrants: Chloride in dialysis and infusion solutions Ag Titrode with Ag2S coating 6.0430.100 30Silver nitrate Titrations in accordance with Pharm. Europe & USP Ag Titrode with Ag2S coating 6.0430.100 30 Determination of hydrogen sulfide, mer- Ag Titrode with Ag2S coating 6.0430.100 30 captans, carbonyl sulfides, sulfides Chloride, bromide, iodide and cyanide in Ag Titrode with Ag2S coating 6.0430.100 30 electroplating baths – Fluoride/hydrofluoric acid in etching baths F -ISE – crystal membrane 6.0502.150 44Complexometry Back titration of excess Ba2+ with EDTA 2+ Ca -ISE polymer membrane 6.0508.110 44Titrants: 2+ 2+ Determination of Ca , Mg in aqueous Ca2+-ISE polymer membrane 6.0508.110 44EDTA, solutions (in accordance with AB 125) ©Complexon 2+ Determination of Al, Ba, Bi, Ca, Cd, Co, Fe, Cu -ISE crystal membrane 6.0502.140 44III and IV Mg, Ni, Pb, ZnPhotometric Color indicators such as xylene orange, N,N- Spectrosense 523 nm 6.5501.100 Titrino 68titrations diethyl-1,4-phenylenediamine, phenol- 6.5501.200 phthalein, thorine, dichlorophenolindophenol Titrando, Titrino plus Color indicators such as dimethylsulfonazo III, Spectrosense 610 nm 6.5501.110 Titrino 68 hydroxy naphthol blue, eriochrome black T, 6.5501.210 HHSNN, diphenylaminosulfonate, murexide Titrando, Titrino plusSurfactants in Titration of anionic and cationic surfactants, Surfactrode Resistant 6.0507.130 48non-aqueous titrations in chloroform, formulations con-media taining oil such as cooling lubricants, drillingAromatic and and cutting oils, oil-containing shower baths,aliphatic hydro- pH < 10carbons, ketones, Titration of anionic and cationic Surfactrode Refill 6.0507.140 48gasoline, kerosene, surfactants, titration of surfactant formula-dichloroethane and tions, washing powders, soaps, pH > 10trichloroethaneSurfactants in Titration of cationic surfactants «Cationic Surfactant» electrode 6.0507.150 48aqueous media Titration of anionic surfactants «Ionic Surfactant» electrode 6.0507.120 48 Titration of non-ionic surfactants NIO electrode 6.0507.010 48 Titration of pharmaceutical ingredients with sodium tetraphenylborate
  • 8. iTrodes – The intelligent electrodes8 The iTrodes The iTrodes of the new intelligent electrode generation 854 iConnect – measuring input «on a chip» The green color of Metrohm has always meant leading confirm Metrohm’s longstanding leadership position in edge technology. Thanks to state-of-the-art electronics the field of potentiometric titration. Metrohm reduces an entire measuring input down to the size of a postage stamp. This means that the complete The electrode used for the titration is the most important measuring input fits in the electrode cable head. It is component of any titration system. But until now, the automatically recognized and identified by its serial electrode, of all things, has represented the last gap in number. traceability. The Titrando with iConnect closes this gap, thus guaranteeing complete traceability of the analytic Digital data transmission result to each component playing a role in the analysis. Directly in the sensor, the analog/dialog converter of the latest generation in the 854 iConnect, converts the ana- Digital identification – Mix-ups are eliminated log measuring signal into binary code. Digital data trans- The built-in memory chip enables the storage of impor- mission means that the measuring signal is no longer tant sensor data such as article number, serial number, susceptible to electrostatic influences. Interference-free calibration data, calibration history, working life and transmission can now always be guaranteed, no matter calibration validity period. how long the electrode cable is. All of the sensor data are uploaded automatically when Just take the measuring input with you! the iTrode is connected to the Titrando. This means that With 854 iConnect the sensor and measuring input are the possibility of any mix-up or editing error is elimi- always calibrated together and the calibration data is nated. stored in the intelligent electrode. As the measuring input is no longer built into the instrument, the electrode The electrode is identified automatically. The user is and 854 iConnect can be used together with different informed if the electrode does not match the one titrators. The calibration procedure is no longer associ- defined in the method. This means that it is not possible ated with a particular titrator. to use an incorrect electrode. iTrodes can be used with the 867 pH module or the 888 Storage of calibration data – no chance for outliers and 90x Titrandos. Monitoring functions allow the exclusion of electrodes whose calibration data lies outside the limits or whose calibration period has already expired. If the sensor is used on different instruments or if one wishes to prevent inexperienced users from having to calibrate the electrode on their own instruments, the electrode can be calibrated on a different instrument under defined conditions. The calibration data in the memory chip make the electrode transferable; it thus does not need to be recalibrated every time it is used with a different instrument.
  • 9. 9Ordering informationiAquatrode Plus with Pt 1000 6.0277.300iUnitrode with Pt 1000 6.0278.300iSolvotrode 6.0279.300iEcotrode plus 6.0280.300iAg Titrode 6.0470.300iAg Titrode with Ag2S coating 6.0470.300SiPt Titrode 6.0471.300iConnect 2.854.0010
  • 10. 10
  • 11. Electrodes for pH measurement/pH titration 11Fine-tune your measurements!The greatest precision and ease of care – these are the two outstanding properties of Unitrode and Aquatrode Plus.The constant electrolyte outflow of the fixed ground joint diaphragm (which is largely insensitive to contamination)guarantees a low-noise measuring signal, even in difficult samples and independent of the measuring conditions.Further details can be found in the theoretical section on page 92.
  • 12. Separate pH glass electrodes12 Separate pH glass electrode Electrically shielded Technical specifications pH range 0...14 Blue T glass for reliable results, e.g. in differential Temperature range 0...80 °C potentiometry in non-aqueous media Installation length 142 mm Optimal length for sample changer applications Shaft diameter 12 mm Minimum immersion depth 15 mm Electrode plug-in head Metrohm plug-in head G Differential potentiometry In addition to the measuring electrode, a reference electrode and an auxiliary electrode are required for differential potentiometry. The shielding of the reference electrode must be identical to that of the measuring electrode. Reference electrodes for differential potentiometry (see «Reference electrodes» section) Ag/AgCl DJ reference electrode, length 125 mm, Metrohm plug-in head G Without electrolyte filling, without cable 6.0729.100 Filled with LiClsat in ethanol, without cable 6.0729.108 Ag/AgCl DJ reference electrode, length 162 mm, Metrohm plug-in head G Without electrolyte filling, without cable 6.0729.110 Auxiliary electrodes for differential potentiometry, Metrohm plug-in head B (see «Separate metal electrodes» section) Separate Pt wire electrode 6.0301.100 Separate Pt pin electrode 6.1241.040 + 6.1248.000 Separate Pt ring electrode 6.0351.100
  • 13. 13Ordering informationSeparated pH glass electrode, without cable 6.0150.100
  • 14. Electrodes for pH measurement14 Primatrode with NTC – the economical entry to GLP-compliant pH measurement Technical specifications Primatrode For solutions that do not contain precipitates, pro- Shaft material PP teins or sulfides pH range 0...14 Long-lasting standard electrode Temperature range 0...80 °C Unbreakable plastic shaft Temperature sensor NTC Impact protection for the glass membrane Diaphragm Ceramic pin Fixed cable (length 1.2 m) Installation length 113 mm LL reference system with long-term stability Shaft diameter 12 mm Variant 6.0228.020 with waterproof plug I for use Minimum immersion depth 15 mm with the 826 pH mobile (IP67) The Solitrode with Pt 1000 – robust and reliable, Technical specifications ideal for routine laboratory use Solitrode For solutions that do not contain precipitates, proteins Shaft material PP or sulfides pH range 0...14 Long-lasting standard electrode Temperature range 0...80 °C Unbrekable plastic shaft Temperature sensor Pt 1000 Impact protection for the glass membrane Diaphragm Ceramic pin Fixed cable (length 1.2 m) Installation length 113 mm LL reference system with long-term stability Shaft diameter 12 mm Minimum immersion depth 15 mm Ecotrode Gel – the maintenance-free solution Technical specifications Ideal for routine measurements in similar samples Ecotrode Gel Maintenance-free Shaft material Glass Life-time indicator pH range 1...11 LL reference system with long-term stability Temperature range 0...60 °C Temperature sensor NTC Diaphragm Twin pore Installation length 125 mm Shaft diameter 12 mm Minimum immersion depth 20 mm Electrode plug-in head Metrohm plug-in head U How to store your electrodes correctly: Rapid response is not a matter of magic, but rather a question of storage! Metrohm recommends the patented 6.2323.000 storage solution for all combined pH glass electrodes which use c(KCl) = 3 mol/L as the reference electrolyte. This prevents the aging of the glass membrane and, as a result, guarantees response times short as they were on the first day. More information on this can be found in the theoretical section in Chapter 1.3.1. «pH glass electrodes.»
  • 15. 15 Primatrode The economical entry to GLP-compliant pH measurement Solitrode Robust and reliable, ideal for routine laboratory use Ecotrode Gel The maintenance-free solutionOrdering informationPrimatrode with NTC, fixed cable with plug F + 1 x 2 mm 6.0228.010Primatrode with NTC, fixed cable with plug I (IP67) + 1 x 2 mm 6.0228.020Solitrode without temperature sensor, without cable 6.0220.100Solitrode with Pt 1000, fixed cable plug F + 2 x 4 mm 6.0228.000Ecotrode Gel with NTC, without cable, plug-in head U 6.0221.600
  • 16. Electrodes for pH measurement16 Unitrode with Pt 1000 – high performance in difficult samples and at high pH values Technical specifications Unitrode For universal use, even in dyes, pigments, inks, suspen- Shaft material Glass sions, resins and polymers pH range 0...14 Fixed ground-joint diaphragm insensitive to contamination Temperature range 0...100 °C High temperature resistance and very low alkali error Temperature sensor Pt 1000 Rapid response to temperature changes Diaphragm Fixed ground joint Outer electrolyte Idrolyte for temperatures of Installation length 113 mm 80...100 °C Shaft diameter 12 mm Fixed cable (length 1.2 m) or with plug-in head U and Minimum immersion depth 25 mm removable cable LL reference system with long-term stability Aquatrode Plus with Pt 1000 – ideal for weekly Technical specifications buffered aqueous solutions Aquatrode Plus Special electrode membrane glass: precise measuring Shaft material Glass values and very rapid response times, even in weekly pH range 0...13 buffered solutions such as drinking water, surface Temperature range 0...60 °C water and rain water and other poorly conducting Temperature sensor Pt 1000 solutions Diaphragm Fixed ground joint Maintenance-free inner reference electrolyte (gel) Installation length 125/260 mm Variable bridge electrolyte for special applications Shaft diameter 12 mm Fixed ground joint diaphragm insensitive to contamination Minimum immersion depth 20 mm Optimized length for sample changer applications Fixed cable (length 2 m) LL reference system with long-term stability Technical specifications EtOH-Trode – the specialist for ethanol EtOH-Trode Developed for pHe measurement in ethanol Shaft material Glass Special membrane glass pH range 0...12 Very precise ground joint diaphragm Temperature range 0...80 °C Double-junction system for free choice of electrolytes Diaphragm Fixed ground joint (e.g. 3 M KCI in ASTM D 6423, 1 M LiCI in EN Installation length 145 mm 15490). Shaft diameter 12 mm LL reference system with long-term stability Minimum immersion depth 20 mm Electrode plug-in head Metrohm plug-in head G Wellness for the electrode Reliable measuring results over long periods of time can only be guaranteed if the glass membrane and the dia- phragm receive preventative and regular care. Cleaning by means of etching with toxic chemicals or a mechanical treatment of the diaphragm is not only complicated and expensive, it also accelerates the aging of the pH glass electrode as well. The 6.2325.000 care kit was developed for simple, gentle cleaning of pH glass electrodes with a liquid electrolyte. Regular application can considerably prolong its lifetime.
  • 17. 17 EtOH-Trode The specialist for pHe measurement Unitrode High performance, even in difficult samples and at high temperatures Aquatrode Plus Rapid response times and greatest precision in poorly buffered solutions due to special electrode glass and fixed ground joint diaphragmOrdering informationUnitrode with Pt 1000, fixed cable plug F + 2 x B (4 mm) 6.0258.000Unitrode with Pt 1000, fixed cable plug F + 2 x 2 mm 6.0258.010Unitrode without temperature sensor, without cable 6.0259.100Unitrode with Pt 1000, without cable, plug-in head U 6.0258.600Aquatrode Plus without temperature sensor, length 125 mm, without cable 6.0253.100Aquatrode Plus without temperature sensor, length 260 mm, without cable 6.0253.120Aquatrode Plus with Pt 1000, length 125 mm, fixed cable plug F + 2 x B (4 mm) 6.0257.000Aquatrode Plus with Pt 1000, length 260 mm, fixed cable plug F + 2 x B (4 mm) 6.0257.020EtOH-Trode without temperature sensor, without cable 6.0269.100
  • 18. Electrodes for pH titration18 Ecotrode Gel – the maintenance-free solution Ideal for routine measurements in similar samples Technical specifications Ecotrode Gel Maintenance-free Shaft material Glass Lifetime indicator pH range 1...11 LL reference system with long-term stability Temperature range 0...60 °C Diaphragm Twin pore Installation length 125 mm Shaft diameter 12 mm Minimum immersion depth 20 mm Electrode plug-in head Metrohm plug-in head G Ecotrode Plus – high durability in routine use at a Technical specifications fair price Ecotrode Plus For acid/base titrations in various kinds of solutions Shaft material Glass Fixed ground joint diaphragm insensitive to contamination pH range 0...13 Ideal for routine laboratory use Temperature range 0...80 °C LL reference system with long-term stability Diaphragm Fixed ground joint Installation length 113 mm Shaft diameter 12 mm Minimum immersion depth 20 mm Electrode plug-in head Metrohm plug-in head G Profitrode – professional working in the most Technical specifications difficult of matrices Profitrode For difficult matrices (galvanic baths, precipitates, Shaft material Glass samples containing sulfides, etc.) pH range 0...14 Flexible ground joint diaphragm, particularly easy to Temperature range 0...80 °C clean Diaphragm Flexible ground joint Double-junction construction Installation length 113/170/310 mm Available in various lengths Shaft diameter 12 mm (113/170/310 mm) Minimum immersion depth 30 mm LL reference system with long-term stability Electrode plug-in head Metrohm plug-in head G Unitrode – high performance in difficult samples Technical specifications and at high pH values Unitrode For universal use, even in dyes, pigments, inks, sus- Shaft material Glass pensions, resins and polymers pH range 0...14 Fixed ground joint diaphragm insensitive to contamination Temperature range 0...100 °C High temperature resistance and very low alkali error Diaphragm Fixed ground joint Rapid response to temperature changes Installation length 113 mm Outer electrolyte Idrolyte for temperatures of Shaft diameter 12 mm 80...100 °C Minimum immersion depth 25 mm LL reference system with long-term stability
  • 19. 19 Ecotrode Gel Maintenance-free pH measurement/ titration Ecotrode Plus High durability in routine use at a fair price Profitrode Professional working in the most difficult matrices Unitrode High performance in difficult samples and at high pH valuesOrdering informationEcotrode Gel without temperature sensor, without cable 6.0221.100Ecotrode Plus, without cable 6.0262.100Profitrode, length 113 mm, without cable 6.0255.100Profitrode, length 170 mm, without cable 6.0255.110Profitrode, length 310 mm, without cable 6.0255.120Unitrode with Pt 1000, fixed cable plug F + 2 x B (4 mm) 6.0258.000Unitrode with Pt 1000, fixed cable plug F + 2 x 2 mm 6.0258.010Unitrode without temperature sensor, without cable 6.0259.100Unitrode with Pt 1000, without cable, plug-in head U 6.0258.600
  • 20. Electrodes for pH titration20 Aquatrode Plus – ideal for aqueous, weekly buffered solutions Technical specifications Aquatrode Plus Precise measuring values and very rapid response Shaft material Glass times in ion-deficient or weekly buffered solutions – pH range 0...13 such as drinking water, surface water and rain water Temperature range 0...60 °C – thanks to special membrane glass and optimized, Diaphragm Fixed ground joint fixed ground joint diaphragm insensitive to contamination Installation length 125/260 mm Maintenance-free inner reference electrolyte (gel) Shaft diameter 12 mm Variable bridge electrolyte for special applications Minimum immersion depth 20 mm Optimized length for sample changer applications Electrode plug-in head Metrohm plug-in head G LL reference system with long-term stability Solvotrode – space-saving alternative for titration Technical specifications in non-aqueous media Solvotrode For non-aqueous titrations in the pharmaceutical sector Shaft material Glass For determination of TAN/TBN in compliance with pH range 0...14 ASTM D4739, D2896 and D664 and DIN ISO 3771 Temperature range 0...70 °C and DIN EN 12634 Diaphragm Flexible ground joint Reference electrolyte: LiCl(sat) in ethanol Installation length 113 mm Rapid response and stable measuring values in Shaft diameter 12 mm organic solvents Minimum immersion depth 20 mm Shielding against electrostatic effects Electrode plug-in head Metrohm plug-in head G Flexible ground joint diaphragm, particularly easy to clean LL reference system with long-term stability Drinking water analysis – Does it matter at which stirring rate titration is performed? When stirring in ion-deficient solutions, streaming potentials occur at pH electrodes with ceramic pin diaphragms which falsify measuring values. In the case of a SET titration, e.g. to a defined pH value, a considerable error can be produced if an incorrect value is measured at the start or at the endpoint of the titration. See page 93 to find out why you can forget about this problem when using the Aquatrode Plus.
  • 21. 21 Solvotrode Space-saving alternative for titration in non-aqueous media Aquatrode Plus Fast response and excellent pre- cision in weekly buffered solu- tions thanks to special membrane glass and fixed ground joint diaphragmOrdering informationSolvotrode, without cable 6.0229.100Aquatrode Plus without temperature sensor, length 125 mm, without cable 6.0253.100Aquatrode Plus without temperature sensor, length 260 mm, without cable 6.0253.120Aquatrode Plus with Pt 1000, length 125 mm, fixed cable plug F + 2 x B (4 mm) 6.0257.000Aquatrode Plus with Pt 1000, length 260 mm, fixed cable plug F + 2 x B (4 mm) 6.0257.020
  • 22. Special electrodes for pH measurement/pH titration22 Biotrode – pH measurement in small volumes Very low immersion depth and very small diameter of Technical specifications Biotrode the electrode tip (3 mm), exceptionally suited to small Shaft material Glass measuring vessels pH range 1...11 For protein-containing samples and solutions with Temperature range 0...60 °C organic components Diaphragm Platinum wire Very low electrolyte outflow (Idrolyte) Installation length 113 mm LL reference system with long-term stability Shaft diameter 12 mm Shaft diameter bottom 3 mm Minimum immersion depth 7 mm Electrode plug-in head Metrohm plug-in head G Spearhead electrode – pH measurement in Technical specifications semi-solid samples Spearhead electrode Robust electrode tip for measurements in semi-solid Shaft material Glass samples such as cheese, meat, fruits, etc. pH range 1...11 Maintenance-free reference electrolyte (gel) Temperature range 0...40 °C Easy-to-clean diaphragm Diaphragm Twin pore LL reference system with long-term stability Installation length 98 mm Shaft diameter 12 mm Shaft diameter bottom 6 mm Minimum immersion depth 10 mm Electrode plug-in head Metrohm plug-in head G Flat-membrane electrode – pH measurement on Technical specifications surfaces and in small sample volumes Flat-membrane electrode For pH measurement on surfaces such as paper, textiles, Shaft material Glass leather or soil samples (aqueous suspensions) pH range 0...14 Measurement/titration in small sample volumes Temperature range 0...80 °C Completely made of glass with extremely fine- Diaphragm Fixed ground joint grounded surface Installation length 125 mm LL reference system with long-term stability Shaft diameter 12 mm Minimum immersion depth 1 mm Electrode plug-in head Metrohm plug-in head G Porotrode – pH measurement in protein contain- Technical specifications ing samples Porotrode For pH measurement in very contaminated, protein- Shaft material Glass containing or viscous samples pH range 0...14 Low-maintenance capillary diaphragm Temperature range 0...80 °C Polymer electrolyte Porolyte for uniform electrolyte Diaphragm Ceramic capillaries outflow Installation length 125 mm LL reference system with long-term stability Shaft diameter 12 mm Minimum immersion depth 20 mm Electrode plug-in head Metrohm plug-in head G
  • 23. 23 Biotrode pH measurement in small volumes Spearhead electrode pH measurement in semi-solid samples Flat-membrane electrode pH measurement on surfaces Porotrode pH measurement in protein-containing samplesOrdering informationBiotrode, without cable 6.0224.100Spearhead pH glass electrode, without cable 6.0226.100Flat-membrane pH glass electrode, without cable 6.0256.100Porotrode, without cable 6.0235.200
  • 24. Special electrodes for pH measurement/pH titration24 Microelectrode – routine use with sample changers and smal vials Technical specifications Microelectrode For simple acid/base titrations in aqueous solutions Shaft material Glass Available in various lengths (113/168 mm) pH range 0...14 LL reference system with long-term stability Temperature range 0...80 °C Diaphragm Ceramic pin Installation length 113/168 mm Shaft diameter 12 mm Shaft diameter bottom 6.4 mm Minimum immersion depth 20 mm Electrode plug-in head Metrohm plug-in head G Viscotrode – universal application in viscous Technical specifications media Viscotrode For viscous protein- or sulfides- containing media Shaft material Glass Flexible ground joint diaphragm, particularly easy to pH range 0...14 clean Temperature range 0...80 °C LL reference system with long-term stability Diaphragm Flexible ground joint Installation length 113 mm Shaft diameter 12 mm Minimum immersion depth 30 mm Electrode plug-in head Metrohm plug-in head G Syntrode with Pt 1000 – use in Technical specifications synthesis and in bioreactors Syntrode Low-maintenance thanks to storage vessel for Shaft material Glass reference electrolytes pH range 0...14 Fixed ground joint diaphragm insensitive to Temperature range 0...100 °C contamination Temperature sensor Pt 1000 High temperature resistance Diaphragm Fixed ground-joint Available in various lengths (288/438 mm) Installation length 288/438 mm Fixed cable (length 2/3 m) Shaft diameter 12 mm LL reference system with long-term stability Minimum immersion depth 25 mm
  • 25. 25 size d in uce red ion trat Illus Microelectrode Routine use with sample changers and small vials Viscotrode Universal use in viscous media Syntrode with Pt 1000 For use in synthesis and in bioreactorsOrdering informationMicroelectrode, length 113 mm, without cable 6.0234.100Microelectrode, length 168 mm, without cable 6.0234.110Viscotrode, without cable 6.0239.100Syntrode with Pt 1000, length 288 mm, fixed cable 2 m, plug F + 2 x B (4 mm) 6.0248.020Syntrode with Pt 1000, length 438 mm, fixed cable 3 m, plug F + 2 x B (4 mm) 6.0248.030
  • 26. 26
  • 27. Metal electrodes 27High-performance metal electrodes for redox and precipitation titration, voltammetry and water determinationaccording to Karl Fischer.
  • 28. Separate metal and carbon electrodes28 Separate Pt-wire electrode Electrode tip made of Pt-wire (0.8 x 6 mm) Technical specifications Separate Pt-wire electrode Auxiliary electrode for differential potentiometry Shaft material Glass Measuring range -2000...2000 mV Temperature range -20...70 °C Installation length 125 mm Shaft diameter 12 mm Minimum immersion depth 10 mm Electrode plug-in head Metrohm plug-in head B Separate double Pt-sheet electrode Technical specifications For bivoltammetric titrations Separate double Pt-sheet electrode For titration with conductometric endpoint recognition Shaft material Glass Measuring range -2000...2000 mV Temperature range -20...70 °C Installation length 101 mm Shaft diameter 12 mm Minimum immersion depth 10 mm Electrode plug-in head Metrohm plug-in head G Separate metal-ring electrodes Separate Ag-ring electrode Technical specifications For precipitation titrations of halides, sulfides, Separate metal-ring electrodes hydrogen sulfide, mercaptans and cyanides Shaft material Glass Available with or without Ag2S coating Measuring range -2000...2000 mV (specify when ordering) Temperature range -20...80 °C Installation length 125 mm Separate Pt-ring electrode Shaft diameter 12 mm For all standard redox titrations Minimum immersion depth 7 mm Electrode plug-in head Metrohm plug-in head G Separate Au-ring electrode For ferrometry (determination of the chemical oxygen demand, COD) For determination of penicillin and ampicillin For titrations with Hg(NO3)2 For redox titrations in the presence of chromium or iron Separate metal-rod electrodes Consisting of separate electrode shaft made of PP Technical specifications and exchangeable metal-rod (76 mm x 2 mm) made Separate metal-rod electrodes of platinum, silver, gold, tungsten or glassy carbon Total length 162 mm Installation length 140 mm Degree of purity Shaft diameter 12 mm Pt 99.90% Shaft diameter bottom 8 mm Ag 99.99% Electrode plug-in head Metrohm plug-in head B Gold 99.99% W 99.95%
  • 29. 29Ordering informationSeparate Pt-wire electrode 6.0301.100Separate double Pt-sheet electrode 6.0309.100Separate Ag-ring electrode 6.0350.100Separate Pt-ring electrode 6.0351.100Separate Au-ring electrode 6.0352.100Shaft for separate meta-rod electrode 6.1241.040Electrode rod Pt 6.1248.000Electrode rod Ag 6.1248.010Electrode rod Au 6.1248.030Electrode rod glassy carbon 6.1248.040Electrode rod W 6.1248.050
  • 30. Titrodes – the maintenance-free metal electrodes30 Pt Titrode / Pt Micro Titrode For redox titrations without alteration of the pH value Technical specifications Titrodes For bromatometry, iodometry and cerimetry in com- Shaft material Glass pliance with Pharm. Europe & USP Measuring range -2000...2000 mV Maintenance-free reference system (pH glass pH range 0...14 membrane) Temperature range 0...80 °C Reference system pH glass electrode Ag Titrode / Ag Micro Titrode Installation length 125 mm For precipitation titrations without alteration of the Shaft diameter 12 mm pH value Minimum immersion depth 20 mm For precipitation titrations of halides, sulfides, Electrode plug-in head Metrohm plug-in head G hydrogen sulfide, mercaptans and cyanides For titrations in compliance with Pharm. Europe & USP Micro Titrodes Available with or without Ag2S coating Shaft material Glass (specify when ordering) Measuring range -2000...2000 mV Maintenance-free reference system (pH glass pH range 0...14 membrane) Temperature range 0...80 °C Reference system pH glass electrode Au Micro Titrode Installation length 178 mm For ferrometry (determination of the chemical oxygen Shaft diameter 12 mm demand, COD) Shaft diameter bottom 6.4 mm For the determination of penicillin and ampicillin Minimum immersion depth 20 mm For titrations with Hg(NO3)2 Electrode plug-in head Metrohm plug-in head G For redox titrations in the presence of chromium or iron Maintenance-free reference system (pH glass membrane) Ag Titrodes: available with or without coating Depending on the application (see application lists), the use of an Ag Titrode with or without Ag2S or AgBr coating is recommended. We would be happy to supply you with your Ag Titrode with the respective coating at an addi- tional charge; please specify when ordering.
  • 31. 31 Titrodes High performance in redox and precipitation titrations without alteration of the pH value Micro Titrodes Optimized length and diameter of the lower part of the electrode for use in earlier Metrohm sample changer systemsOrdering informationAg Titrode, without cable 6.0430.100Ag Titrode, with Ag2S coating, without cable 6.0430.100SAg Titrode, with AgBr coating, without cable 6.0430.100BrPt Titrode, without cable 6.0431.100Micro Ag Titrode, without cable 6.0433.110Micro Pt Titrode, without cable 6.0434.110Micro Au Titrode, without cable 6.0435.110
  • 32. Combined metal electrodes32 Combined Ag-ring electrode For precipitation titrations of halides, sulfides, Technical specifications Combined Ag-ring electrode hydrogen sulfide, mercaptans and cyanides with Shaft material Glass alteration of the pH value Measuring range -2000...2000 mV Available with or without Ag2S coating Temperature range -5...80 °C (specify when ordering) Reference system Ag wire + AgCl Reference electrolyte c(KNO3) = 1 mol/L Combined Pt-ring electrode Diaphragm Ceramic pin For redox titrations with alteration of the pH value Installation length 113 mm Shaft diameter 12 mm Combined Au-ring electrode Minimum immersion depth 15 mm For ferrometry (determination of the chemical oxygen Electrode plug-in head Metrohm plug-in head G demand COD) For determination of penicillin and ampicillin Combined Pt-ring electrode / Au-ring electrode Shaft material Glass Measuring range -2000...2000 mV Temperature range -5...80 °C Reference system LL system Reference electrolyte c(KCl) = 3 mol/L Diaphragm Ceramic pin Installation length 113 mm Shaft diameter 12 mm Minimum immersion depth 15 mm Electrode plug-in head Metrohm plug-in head G Combined Sb electrode Technical specifications For pH titration in very hygroscopic matrices or in Combined Sb electrode matrices containing hydrofluoric acid Shaft material PP Unbreakable plastic shaft pH range 2...11 Temperature range 0...70 °C Reference system LL system Reference electrolyte c(KCl) = 3 mol/L Diaphragm Ceramic pin Installation length 113 mm Shaft diameter 12 mm Minimum immersion depth 15 mm Electrode plug-in head Metrohm plug-in head G
  • 33. 33 Combined metal-ring electrodes High performance with redox and precipitation titrations with alteration of the pH value Combined Sb electrode pH titration in solutions con- taining hydrofluoric acidOrdering informationCombined Ag-ring electrode, without cable 6.0450.100Combined Ag-ring electrode, with Ag2S coating, without cable 6.0450.100SCombined Pt-ring electrode, without cable 6.0451.100Combined Au-ring electrode, without cable 6.0452.100Combined Sb-ring electrode, without cable 6.0421.100
  • 34. Electrodes for voltammetry34 The electrodes described in the following can be used in various Metrohm voltammetry instruments: 663 VA Stand, 694 VA Stand, 747 VA Stand, 757 VA Computrace and 797 VA Computrace. MME – Multi-Mode electrode Ordering information Universally applicable working electrode for MME – Multi-Mode Electrode 6.1246.020 polarography and voltammetry Glass capillaries, not silanized, 10 units 6.1226.030 Determination of heavy metal ions, organic Glass capillaries, silanized, 10 units 6.1226.050 substances, anions Determination range: ppm to ppt Universal, robust, durable, easy maintenance, no electrochemical conditioning required Supplied without glass capillaries Glass capillaries Non-silanized glass capillaries Standard capillary for polarography and stripping voltammetry in alkaline solutions For universal use with all pH values in aqueous and non-aqueous solutions Silanized glass capillaries Silanized capillaries for stripping voltammetry in acidic to mildly alkaline solutions Stable drop formation in acidic or mildly alkaline solutions (pH < 10). Applications with large mercury drops and/or long accumulation times Long lifetime
  • 35. RDE – rotating disc electrodesAn RDE consists of a driving axle and an exchangeable 35electrode tip.Ordering informationDrive for rotating disc electrode (RDE) 6.1204.210Drive for rotating disc electrode (RDE) 6.1204.220with titanium axle and mercury contactStopper 6.2709.040Electrode tips for the RDEOrder number Electrode tip Applications Determination range6.1204.180 Ultratrace graphite Analysis of heavy metals with anodic ppb to ppt stripping voltammetry (mercury film technique) and with adsorptive stripping voltammetry (without the use of mercury film)6.1204.110 Glassy carbon Analysis of heavy metals with anodic ppb to ppt stripping voltammetry (mercury film technique), kinetic and thermodynamic studies in electrochemistry6.1204.120 Platinum Kinetic and thermodynamic ppm to ppt Ø 2 mm unpolished studies in electrochemistry6.1204.130 Silver Analysis of halogenides and pseudohalogenides ppb to ppt6.1204.140 Gold Analysis of mercury and other metal ions ppb to ppt with anodic stripping voltammetry6.1204.150 Gold With laterally fitted electrode for arsenic ppb to ppt determination with anodic stripping voltammetry in compliance with Application Bulletin 2266.1204.160 Platinum Analysis of organic additives in electroplating ppm to ppt Ø 2 mm baths with cyclic voltammetric stripping polished technique (CVS), kinetic and thermodynamic studies in electrochemistry6.1204.170 Platinum Analysis of organic additives in galvanic ppm to ppt Ø 3 mm baths with cyclic voltammetric stripping polished technique (CVS), kinetic and thermodynamic studies in electrochemistry6.1204.190 Platinum Analysis of organic additives in galvanic ppm to ppt Ø 1 mm baths with cyclic voltammetric stripping polished technique (CVS), kinetic and thermodynamic shaft in glass studies in electrochemistry analysis6.1204.610 Platinum Analysis of organic additives in electroplating ppm to ppt Ø 2 mm baths with cyclic voltammetric stripping polished technique (CVS), kinetic and thermodynamic shaft in glass studies in electrochemistry
  • 36. Electrodes for voltammetry36 Reference electrode for Metrohm VA stands Reference electrode made of plastic with ceramic Ordering information diaphragm, filled Universal double-junction reference electrode for Ag / AgCl reference electrode 6.0728.020 voltammetry Electrolyte vessel for Reference electrode 6.1245.010 Inner system filled with c(KCl) = 3 mol/L Aqueous solutions, trace and ultra trace ranges, CVS Low carry-over effects, low blank values Reference electrode made of plastic with ceramic diaphragm, dry Double-junction reference electrode. Reference system dry Ag / AgCl reference electrode (dry) 6.0728.010 Studies in organic solvents with any electrolyte solution Electrolyte vessel for reference electrode 6.1245.010 Low carry-over effects, low blank values LL reference electrode made of plastic with ceramic diaphragm, filled Double-junction reference electrode for the analysis LL-Ag/AgCl reference electrode 6.0728.030 of electroplating baths with cyclic voltammetric Electrolyte vessel for reference electrode 6.1245.010 stripping (CVS) LL-Ag/AgCl (Gel) reference electrode 6.0728.040 Inner system filled with c(KCl) = 3 mol/L Electrolyte vessel for reference electrode 6.1245.010 Very stable reference potential LL reference electrode made of glass, filled Double-junction reference electrode for the studies LL-Ag/AgCl (Gel) reference electrode 6.0730.000 of electroplating baths with cyclic voltammetric stripping (CVS) Very stable reference potential Maintenance-free Reference electrode made of glass with ground joint diaphragm Double-junction reference electrode with dry LL-Ag/AgCl(Gel) reference electrode glass 6.0728.000 reference system Electrolyte vessel for reference electrode 6.1245.010 For aqueous as well as non-aqueous solutions Simple electrolyte replacement, low outflow rate Auxiliary electrodes for Metrohm VA stands Platinum auxiliary electrode Universal auxiliary electrode for voltammetry Platinum auxiliary electrode 6.0343.000 For all applications with the MME as well as with the rotating platinum disc electrode Robust, easy maintenance Glassy carbon auxiliary electrode For all applications with rotating disc electrodes as Auxiliary electrode holder 6.1241.020 well as with the MME Glassy carbon rod 6.1247.000 Inert surface, no contamination of the measuring cell by platinum
  • 37. 6.1245.010 6.0728.010 + 6.0728.020 37 6.0728.000 6.0728.030 6.0728.040 6.1245.000 6.0730.000 6.0343.000 6.1241.020 6.1247.000 6.1204.3XXWorking electrodes for the Autolab RDEOrder number Electrode tip Applications Determination range6.1204.300 Glassy carbon Analysis of heavy metals with anodic ppb to ppt stripping voltammetry (mercury film technique), kinetic and thermodynamic studies in electrochemistry6.1204.310 Platinum Kinetic and thermodynamic studies in electrochemistry6.1204.320 Gold Analysis of mercury and other metal ions ppm to ppt with anodic stripping voltammetry6.1204.330 Silver Analysis of halogenides and pseudohalogenides ppb to ppt
  • 38. Electrodes for Karl Fischer titration38 Double platinum-wire indicator electrodes Indicator electrode for volumetric KF determination Technical specifications For KFT equipment in the Titrino line, Titrandos and Measuring range -2000...2000 mV Titro processors Temperature range -20...70 °C For «Ipol»-mode titrations Installation length 96 mm Also for 685 and 737 KF Coulometer Shaft diameter 8 mm Minimum immersion depth 5 mm Electrode plug-in head Metrohm plug-in head G Indicator electrode for 756 and 831 KF Technical specifications coulometer and 851 and 852 Titrandos Measuring range -2000...2000 mV With standard ground joint 14/15 Temperature range -20...70 °C Installation length 101 mm Shaft diameter 12 mm Shaft diameter bottom 8.75 mm Minimum immersion depth 10 mm Electrode plug-in head Metrohm plug-in head G Indicator electrode for KF Sample Changers Technical specifications Fixed cable (length 2 m with plug F) Measuring range -2000...2000 mV Temperature range -20...70 °C Installation length 103 mm Shaft diameter 5.3 mm Minimum immersion depth 10 mm
  • 39. 39Ordering informationIndicator electrode for 684 + 737 KF Coulometers 6.0338.100Indicator electrode for 756 + 831 KF Coulometers 6.0341.100Indicator electrode for 814 + 815 KF Sample Changers 6.0340.000
  • 40. Electrodes for Karl Fischer titration40 Generator electrodes Generator electrode with diaphragm Technical specifications for 684 + 737 KF Coulometers Temperature range -20...70 °C Fixed cable (length 1 m, plug H) Installation length 65 mm Shaft diameter 24 mm Minimum immersion depth 15 mm Generator electrode without diaphragm Technical specifications for 684 + 737 KF Coulometers Temperature range -20...70 °C Standard ground joint 29/22 and Metrohm plug-in Installation length 110 mm head G Shaft diameter 24 mm Requires cable 6.2104.120 for connection with KF Minimum immersion depth 15 mm Coulometers Generator electrode with diaphragm for 756 + Technical specifications 831 KF Coulometers and 851 + 852 Titrandos Temperature range -20...70 °C Standard ground joint 29/22 and Metrohm plug-in Installation length 100 mm head G Shaft diameter 24 mm Requires cable 6.2104.120 for connection with KF Minimum immersion depth 15 mm Coulometers Generator electrode without diaphragm for 756 + Technical specifications 831 KF Coulometers and 851 + 852 Titrandos Temperature range -20...70 °C Standard ground joint 29/22 and Metrohm plug-in Installation length 100 mm head G Shaft diameter 24 mm Requires cable 6.2104.120 for connection with KF Minimum immersion depth 15 mm Coulometers
  • 41. 41 6.0339.000 6.0342.110 Illustrations reduced in size 6.0344.100 6.0345.100Ordering informationGenerator electrode with diaphragm for 684 + 737 KF Coulometers 6.0339.000Generator electrode without diaphragm for 684 + 737 KF Coulometers 6.0342.110Generator electrode with diaphragm for 756 + 831 KF Coulometers 6.0344.100and 851 + 852 TitrandosGenerator electrode without diaphragm for 756 + 831 KF Coulometers 6.0345.100and 851 + 852 Titrandos
  • 42. 42
  • 43. 43Electrodes for ion and surfactant analysis
  • 44. Ion-selective electrodes44 Polymer-membrane electrodes with replaceable electrode tip for K+ and NO3– Robust construction High selectivity due to ionophores immobilized in the membrane Short preparation time after conditioning in a standard solution For aqueous solutions Crystal-membrane electrodes Robust construction Can also be used for brief periods in organic solvents Simple cleaning and renewal of electrode surface with polishing set Sodium-selective glass membrane electrode For sodium determination in simple aqueous media Polymer-membrane electrodes for Na+ and Ca2+ Robust construction High selectivity due to ionophores immobilized in the membrane Short preparation time after conditioning in a standard solution For aqueous solutions Ammonia-selective gas-membrane electrode Robust construction Short preparation time after conditioning in a standard solution The gas-permeable Teflon membrane ensures high selectivity and prevents interferences by the measur- ing solution Rapid exchange of Teflon membrane thanks to ready-for-use certified membrane modules
  • 45. 45 Ion Article no. Membrane Min. Installation- Shaft- Tempera- Measure- pH range material immersion length diameter ture range ment range depth (mm) (mm) (mm) (°C) (mol/L) Ag+ 6.0502.180 Crystal 1 123 12 0...80 10–7...1 2...8 Br– 6.0502.100 Crystal 1 123 12 0...50 5*10–6...1 0...14 Ca2+ 6.0508.110 Polymer 1 123 12 0...40 5*10–7...1 2...12 Cd2+ 6.0502.110 Crystal 1 123 12 0...80 10–7...10–1 2...12 Cl– 6.0502.120 Crystal 1 123 12 0...50 5*10–5...1 0...14 CN– 6.0502.130 Crystal 1 123 12 0...80 8*10–6...10–2 10...14 Cu2+ 6.0502.140 Crystal 1 123 12 0...80 10–8...10–1 2...12 F– 6.0502.150 Crystal 1 123 12 0...80 10–6...sat. 5...7 I– 6.0502.160 Crystal 1 123 12 0...50 5*10–8...1 0...14 K+ 6.0504.110 Polymer1 1 123 12 0...40 10–6...1 2.5...11 Na+ 6.0501.100 Glass 15 863 12 0...80 10–5...1 5...9 Na+ 6.0508.100 Polymer 1 123 12 0...40 10–6...1 3...12 NH4+ 6.0506.100 Gas membrane 1 123 12 0...50 5*10–7...1 11 NO3– 6.0504.120 Polymer1 1 123 12 0...40 7*10–6...1 2.5...11 Pb2+ 6.0502.170 Crystal 1 123 12 0...80 10–6...10–1 4...7 S2– 6.0502.180 Crystal 1 123 12 0...80 10–7...1 2...12 SCN– 6.0502.190 Crystal 1 123 12 0...50 5*10–6...1 2...101 Electrode with exchangeable electrode tip2 Electrode shaft 6.1241.050 and electrode tip 6.1205.040 must be ordered separately.3 Up to standard ground joint
  • 46. Accessories for ion-selective electrodes46 LL ISE reference, without cable 6.0750.100 Double-junction Ag/AgCl reference electrode with fixed LL ISE Reference A stable, reproducible reference potential is very impor- ground-joint diaphragm and optimized length for sample tant at low ion concentrations, low ionic strengths and changer applications. Standard bridge electrolyte: especially with repeated determinations using sample c(KCl) = 3 mol/L. changer systems. For this reason Metrohm recom- mends reference electrodes with a fixed ground-joint diaphragm for working with ion-selective electrodes. In addition to a constant electrolyte outflow of approx. 5...30 μL/h, these electrodes are also considerably less influenced by either the ionic strength of the sample solution or the stirring speed than other types of refer- ence electrodes. Polymer-membrane electrodes with exchangeable electrode tip 6.1241.050 Electrode shaft for polymer- membrane electrodes 6.0504.XXX 6.1205.020 Polymer-membrane electrode tip K+ Illustration reduced in size 6.1205.030 Polymer-membrane electrode tip NO3– 6.1255.000 Membrane module kit for 6.0506.100, consisting of 3 membrane modules + 50 mL inner electrolyte Other accessories 6.2802.000 Polishing set for crystal-membrane electrodes 6.0502.1X0 Illustration reduced in size (approx. 2 g AI2O3 and polishing cloth) Ion standards (250 mL each), c(Ion) = 0.1000 ± 0.0005 mol/L (traceable to NIST) KBr 6.2301.000 NaCl 6.2301.010 Cu(NO3)2 6.2301.020 NaF 6.2301.030 KI 6.2301.040 KCl 6.2301.060 CaCl2 6.2301.070 KNO3 6.2301.080 Pb ion standard 1.000 g/L ± 0.5% (250 mL) Pb (1.000 g/L) 6.2301.100
  • 47. 47Spoilt for choice!To what must I pay particular attention in an ion determination? Precision? Time needed? Costs?Which method is the most suitable for my application? Titration? Direct measurement? Standard addition?ISA? TISAB? When is their use advisable? Which solution do I need for my application? You will find the answers tothese questions along with many other useful tips for ion determination with ion-selective electrodes from Metrohmin the theoretical part in section 1.3.3. «Ion-selective electrodes.»
  • 48. Electrodes for surfactant titration48 Surfactant electrodes for two-phase titration Surfactrode Refill Technical specifications Refillable surfactant electrode for the titration of ionic Shaft material PEEK surfactants in non-aqueous solvents pH range 0...13 Renewable electrode surface, therefore practically Temperature range 0...40 °C unlimited working life Installation length 125 mm Resistant to virtually all conventional solvents used in Shaft diameter 12 mm surfactant analysis (not to chloroform) Minimum immersion depth 1 mm Particularly suitable for titration of detergents and soap Electrode plug-in head Metrohm plug-in head G Surfactrode Resistant Technical specifications Durable surfactant electrode for the two-phase Shaft material POM titration of anionic and cationic surfactants in pH range 0...10 non-aqueous solvents Temperature range 10...50 °C Easy to clean and low-maintenance, therefore particularly Installation length 108 mm suitable for use in sample changer systems Shaft diameter 12 mm Resistant to chloroform and all solvents used in sur- Minimum immersion depth 5 mm factant analysis Electrode plug-in head Metrohm plug-in head G Particularly suitable for samples containing oil such as drilling and cutting oils or cooling lubricants Polymer-membrane surfactant electrodes for environmentally-friendly surfactant titration Cationic Surfactant electrode Technical specifications For the titration of cationic and anionic surfactants in Shaft material PVC aqueous matrices pH range 0...12 Optimized for cationic surfactants Temperature range 0...40 °C Excellent response due to ionophores immobilized in Installation length 125 mm the membrane Shaft diameter 12 mm Long working life with normal use Shaft diameter bottom 2.5 mm Length of the active part 50 mm Electrode plug-in head Metrohm plug-in head G Ionic Surfactant electrode Technical specifications For the titration of anionic and cationic surfactants in Shaft material PVC aqueous matrices pH range 0...12 Excellent response due to ionophores immobilized in Temperature range 0...40 °C the membrane Installation length 125 mm Long working life with normal use Shaft diameter 12 mm Shaft diameter bottom 2.5 mm Length of the active part 50 mm Electrode plug-in head Metrohm plug-in head G NIO surfactant electrode Technical specifications For the titration of non-ionic surfactants in aqueous matrices Shaft material PVC For the titration of surfactants based on polyoxy- pH range 0...12 ethylene adducts Temperature range 0...40 °C For the titration of pharmaceutical ingredients Installation length 125 mm Long working life with normal use Shaft diameter 12 mm Shaft diameter bottom 2.5 mm Length of the active part 50 mm Electrode plug-in head Metrohm plug-in head G
  • 49. 49Ordering informationSurfactrode Resistant, without cable 6.0507.130Surfactrode Refill, without cable 6.0507.140NIO surfactant electrode, without cable 6.0507.010Ionic Surfactant electrode, without cable 6.0507.120Cationic Surfactant electrode, without cable 6.0507.150
  • 50. Accessories for surfactant electrodes50 Refill set for Surfactrode Refill Paste for Surfactrode Refill, 3.5 g 6.2319.000 Filling tool 6.2826.010 Reagents for surfactant titration TEGO trant A100, titrant for anionic surfactants 6g 6.2317.000 60 g 6.2317.010 500 g 6.2317.020 TEGO add, additive for two-phase titration 50 mL 6.2317.100 500 mL 6.2317.110
  • 51. 51
  • 52. 52
  • 53. 53Reference electrodes – our best references
  • 54. Reference electrodes54 Double-junction reference electrodes Ag/AgCl reference electrode with Metrohm Technical specifications plug-in head B Shaft material Glass Easy to change reference and bridge electrolytes Temperature range 0...80 °C Variable electrolyte outflow at the flexible ground Diaphragm Flexible ground joint joint diaphragm Installation length 97/140 mm Available with 125 mm or 162 mm shaft length Shaft diameter 12 mm With standard ground joint 14/15 Minimum immersion depth 10 mm Can also be supplied filled with electrolyte upon request Reference system Ag wire + AgCl Electrode plug-in head Metrohm plug-in head B Ag/AgCl reference electrode with Metrohm Technical specifications plug-in head G Shaft material Glass For differential potentiometry with Metrohm titrators Temperature range 0...80 °C Easy to change reference and bridge electrolytes Diaphragm Flexible ground joint Variable electrolyte outflow at the flexible ground Installation length 97/140 mm joint diaphragm Shaft diameter 12 mm Available with 125 mm or 162 mm shaft length Minimum immersion depth 10 mm With standard ground joint 14/15 Reference system Ag wire + AgCl Electrode plug-in head Metrohm plug-in head G LL ISE Reference Technical specifications Double-junction Ag/AgCl reference electrode Shaft material Glass High signal stability thanks to constant, reproducible Temperature range 0...80 °C electrolyte outflow, therefore particularly suitable for Diaphragm Fixed ground joint sample changer applications Installation length 125 mm Fixed ground joint diaphragm insensitive to Shaft diameter 12 mm contamination Minimum immersion depth 1 mm Minimum immersion depth of 1 mm Reference system Ag wire + AgCl Electrode plug-in head Metrohm plug-in head B
  • 55. 55Ordering informationAg/AgCl DJ reference electrode with Metrohm plug-in head BLength 125 mm, without electrolyte filling, without cable 6.0726.100Length 125 mm, filled with c(KCl) = 3 mol/L, without cable 6.0726.107Length 162 mm, without electrolyte filling, without cable 6.0726.110Ag/AgCl DJ reference electrode with Metrohm plug-in head GLength 125 mm, without electrolyte filling, without cable 6.0729.100Length 125 mm, filled with LiClsat in ethanol, without cable 6.0729.108Length 162 mm, without electrolyte filling, without cable 6.0729.110LL ISE reference, without cable 6.0750.100
  • 56. Reference electrodes56 Modular reference system Consisting of Ag/AgCl reference system with standard Technical specifications Ag/AgCl reference system ground joint 14/15 and exchangeable electrolyte vessel Shaft material Glass Temperature range 0...80 °C Electrolyte vessel made of glass with storage vessel Shaft length 50 mm (approx. 5 mL) and glass fritt Length to the upper edge Standard ground joint 43 mm Electrolyte vessels without storage vessels, with Shaft diameter top 12 mm ceramic diaphragm, various diaphragm diameters Shaft diameter bottom 8 mm Minimum immersion depth 20 mm Reference system Ag wire + AgCl Electrode plug-in head Metrohm plug-in head B Electrolyte vessel with storage container Length to the upper edge Standard ground joint 101 mm Shaft diameter 6 mm Shaft material Glass Diaphragm Fritted glass P4 Electrolyte vessels without storage container Length to the upper edge Standard ground joint 101 mm Shaft material PTFE/glass Diaphragm Ceramic pin Shaft diameter 3/5.5 mm Diaphragm diameter 3 mm (PTFE)/1 mm (glass)
  • 57. 57Ordering informationAg/AgCl reference system, without cable 6.0724.140Electrolyte vessel made of glass with storage vessel 6.1225.010Electrolyte vessel made of PTFE without storage vessel, diaphragm diameter 3 mm 6.1240.000Electrolyte vessel made of glass without storage vessel, diaphragm diameter 1 mm 6.1240.020
  • 58. 58
  • 59. 59Conductivity measuring cells and temperature sensors
  • 60. Conductivity measuring cells60 Five-ring conductivity measuring cells Modern five-ring conductivity measuring cells have Technical specifications 6.0915.100 linearity ranges that are wider than those of classic con- Shaft material PEEK ductivity measuring cells and require no additional plati- Ideal measuring range 5...2 x 104 μS/cm nization. The current applied to the inner electrode gen- Temperature range 0...70 °C erates a current flow to the outer, grounded electrodes, Temperature sensor Pt 1000 so that external influences and measuring errors are Installation length 125 mm minimized. Shaft diameter 12 mm Minimum immersion depth 34 mm Five-ring conductivity measuring cells supply precise Cell constant 0.7 cm-1 measuring values, independent of immersion depth or positioning in the beaker (wall effect). Interferences with Technical specifications the potentiometric measurements are now a thing of the 6.0915.130 past; conductivity and pH value can now be measured Shaft material PEEK simultaneously in the same beaker. Ideal measuring range 5...105 μS/cm Temperature range 0...70 °C The measuring cells are equipped with plug N for direct Temperature sensor Pt 1000 connection to the 856 Conductivity Module. Installation length 142 mm Shaft diameter 12 mm Minimum immersion depth 50 mm Cell constant 1 cm-1
  • 61. 61Ordering informationFive-ring conductivity measuring cell c = 0.7 cm-1 with integrated Pt 1000 6.0915.100Five-ring conductivity measuring cell c = 1.0 cm-1 with integrated Pt 1000 6.0915.130
  • 62. Conductivity measuring cells62 Conductivity measuring cells without temperature sensors Conductivity measuring cell, c = 0.1 cm–1 Technical specifications Platinized Shaft material Glass Fixed cable (1 m) with 2 x plug B Measuring range 10-1...104 μS/cm Temperature range 5...70 °C Installation length 108 mm Shaft diameter 12 mm Shaft diameter bottom 20 mm Minimum immersion depth 50 mm Conductivity measuring cell, c = 10 cm–1 Technical specifications Platinized Shaft material Glass Fixed cable (1 m) with 2 x plug B Measuring range 10...106 μS/cm Temperature range 5...70 °C Installation length 125 mm Shaft diameter 12 mm Shaft diameter bottom 20 mm Minimum immersion depth 80 mm Conductivity measuring cell, c = 0.9 cm–1 Technical specifications Platinized Shaft material Glass With standard ground joint 14/15 Measuring range 1...105 μS/cm Metrohm plug-in head G Temperature range 5...70 °C Optimum length for sample changer systems Installation length 120 mm Shaft diameter 12 mm Minimum immersion depth 16 mm
  • 63. 63Ordering informationConductivity measuring cell, c = 0.1 cm–1 6.0901.040Conductivity measuring cell, c = 10 cm–1 6.0901.260Conductivity measuring cell for sample changer, c = 0.9 cm–1, without cable 6.0910.120
  • 64. Conductivity measuring cells64 Conductivity measuring cells with temperature sensor Conductivity measuring cell Technical specifications Shaft material Glass with Pt 100, c = 0.8 cm–1 Measuring range 1...105 μS/cm Platinized Temperature range 5...70 °C Fixed cable (1.2 m) with 4 x plug B Installation length 123 mm Shaft diameter 12 mm Minimum immersion depth 40 mm Conductivity measuring cell Technical specifications with Pt 1000, c = 0.8 cm–1 Shaft material PP Platinized Measuring range 1...105 μS/cm Fixed cable (1.2 m) with 4 x plug B Temperature range 5...70 °C Installation length 125 mm Shaft diameter 12 mm Minimum immersion depth 40 mm Conductivity measuring cell made of stainless Technical specifications steel with Pt 1000, c = 0.1 cm–1 Shaft material Stainless steel Stainless-steel measuring cell for the measurement of Measuring range 0...300 μS/cm very low conductivities Temperature range 0...70 °C Ideal for applications in accordance with USP 645 Installation length 125 mm and EP 2.2.38 Shaft diameter 12 mm Fixed cable (1.2 m) with 4 x plug B or 1 x plug N (for Minimum immersion depth 40 mm 856 Conductivity Module) Conductivity measuring cells for stability measur- Technical specifications ing devices 679, 743, 763 and 873 Shaft material PP Conductivity measuring cell for 679 Rancimat Measuring range 1...105 μS/cm Cell constant c = 0.9 cm–1 Temperature range -20...70 °C With fixed cable (0.4 m) and special connection for Installation length 125 mm 679 Rancimat Shaft diameter 12 mm Minimum immersion depth 30 mm Conductivity measuring cell for 743 Rancimat, Technical specifications 873 Biodiesel Rancimat and 763 PVC Thermomat Shaft material PP Cell constant c = 1 cm–1 Measuring range 1...105 μS/cm Accessories for conductivity measuring cells: Conductivity standard = 12.87 mS/cm (25° C), 250 ml 6.2301.060 Conductivity standard = 100 μS/cm (25 °C), 250 ml with DKD certificate 6.2324.010 Conductivity standard = 100 μS/cm (25 °C), 5 x 30 ml with DKD certificate 6.2324.110
  • 65. 65 Illustration reduced in sizeOrdering informationConductivity measuring cell with Pt 100, c = 0.8 cm–1 6.0908.110Conductivity measuring cell with Pt 1000, c = 0.8 cm–1 6.0912.110Conductivity measuring cell made of stainless steel with Pt 1000, c = 0.1 cm–1, 4 x plug B 6.0914.040Conductivity measuring cell made of stainless steel with Pt 1000, c = 0.1 cm–1, plug N 6.0916.040for 856 Conductivity ModuleConductivity measuring cell for 679 Rancimat 6.0911.120Conductivity measuring cell for 743, 763 and 873 6.0913.130
  • 66. Temperature sensor66 Temperature sensor Pt 1000 Rapid, precise temperature setting Technical specifications Shaft material Glass Available in various lengths (125/178 mm) Temperature range -50...180 °C Installation length 125/178 mm Shaft diameter 12 mm Shaft diameter bottom 5/6.4 mm Minimum immersion depth 20 mm Electrode plug-in head Metrohm plug-in head G Temperature sensor Pt 1000 steel Technical specifications The glass-free alternative Shaft material PEEK Shaft made of PEEK Temperature range -50...100 °C For use in non-oxidizing media pH 1 - 13 Installation length 140 mm For temperature measurement in semi-solid materials Shaft diameter 12 mm such as cheese, not in frozen meat or similar Shaft diameter bottom (75 mm) 3 mm Fixed cable 1.2 m with plug 2 x 2 mm Minimum immersion depth 10 mm Temperature sensor Pt 100 for 711 Liquino, Technical specifications 743 Rancimat or 763 PVC Thermomat Shaft material Stainless steel Shaft made of stainless steel Temperature range -200...300 °C Fixed cable with Mini DIN plug Installation length 178 mm Shaft diameter 2 mm Minimum immersion depth 20 mm Temperature sensor Pt 100 for Technical specifications 873 Biodiesel Rancimat Temperature range -200...300 °C Shaft made of stainless steel Installation length 300 mm Fixed cable with Mini DIN plug Shaft diameter 2 mm Minimum immersion depth 20 mm
  • 67. 67Ordering informationTemperature sensor Pt 1000, length 125 mm, without cable 6.1110.100Temperature sensor Pt 1000, length 178 mm, without cable 6.1110.110Temperature sensor Pt 1000, steel, length 140 mm, plug 2 x 2 mm 6.1114.010Temperature sensor Pt 100 for 711/743/763, length 175 mm 6.1111.010Temperature sensor Pt 100 for 873, length 300 mm 6.1111.020
  • 68. Sensors for photometry68 Titration with photometric endpoint detection is an integral part of many titration methods. The Spectrosense Technical specifications Width (housing) Spectrosense 50.3 mm is a handy sensor that can be used like any other Height (housing) 63 mm Metrosensor. Modern light diodes (LEDs) are used as the Depth (housing) 20.3 mm light-source. The average working life is 50’000 hours. Weight 120 g Even after long use they will still provide high light inten- Material (housing) Aluminum sity. The power supply to the Spectrosense is provided Shaft diameter 12 mm through the stirrer connection for the titrator; no sepa- Material (optical fiber) PMMA rate power supply is required. Two wavelengths are avail- Length without mirror 129 mm able (523 and 610 nm) enabling a wide range of applica- Length with mirror 145 mm tions. Shaft material PEEK Optical path 22 mm Material mirror holder Stainless steel Measuring range 50...1000 mV Temperature range 0...45 °C (housing) Temperature range 0...80 °C (mirror) Relative humidity < 80% pH range 0...14 Photometric titrations with the Spectrosense: typical applications Determination Matrix Color indicator Wavelength Al Sodium borate Xylenol orange 523 nm Free chlorine Water N,N-Diethyl-1,4-phenylenediamine 523 nm Acid value Plastic Phenolphthalein 523 nm Sulfate Fertilizer Thorine 523 nm Vitamin C Tablets Dichlorphenol indophenol 523 nm Ba/Y/Cu Superconductor Dimethylsulfonazo III 610 nm Ca traces Brine Hydroxynaphthol blue 610 nm Ca/Mg Dolomite, drinking water Eriochrome black T 610 nm Fe Mn ores Diphenylaminosulfonate 610 nm Zn Ni baths Murexide 610 nm Accessories Spectrosense 523 nm measuring module 6.1109.100 Spectrosense 610 nm measuring module 6.1109.110 Mirror for Spectrosense (light path 22 mm) 6.1250.010 Power supply cable Titrino – Spectrosense 6.2108.130 Power supply cable Titrando/Titrino plus – Spectrosense 6.2151.070 Cable for measuring input, plug F/angled plug F, length 1 m 6.2116.020
  • 69. 69Ordering informationSpectrosense 523 nm for Titrino, complete, with mirror (light path 22 mm) 6.5501.100and all required cablesSpectrosense 610 nm for Titrino, complete, with mirror (light path 22 mm) 6.5501.110and all required cablesSpectrosense 523 nm for Titrando/Titrino plus, complete, with mirror (light path 22 mm) 6.5501.200and all required cablesSpectrosense 610 nm for Titrando/Titrino plus, complete, with mirror (light path 22 mm) 6.5501.210and all required cables
  • 70. 70
  • 71. 71Accessories for Metrosensors
  • 72. Accessories for Metrosensors72 SGJ sleeves for Metrohm electrodes 6.1236.020 SGJ sleeve made of PP, standard ground joint 14/15 with O-ring 6.1236.030 SGJ sleeve made of PP, standard ground joint 14/15 with O-ring, for sample changer 6.1236.040 SGJ sleeve made of silicone rubber, standard ground joint 14/15 6.1236.050 SGJ sleeve made of PE, standard ground joint 14/15 Other accessories 6.2008.040 Storage vessel made of PE Length 130 mm Diameter 16 mm Ground joint taper or standard ground joint 14/15 6.1243.020 Spare ground joint diaphragm for Profitrode 6.0255.1XX (glass sleeve and plastic ring) 6.1243.030 Spare ground joint for reference electrodes 6.0726.1XX and 6.0729.1XX 6.2615.050 Electrode holder for 11 electrodes and 3 x 50 ml buffer bottles Illustrations reduced in size
  • 73. 736.1236.020 6.1236.030 6.1236.040 6.1236.050
  • 74. Ion standards, buffer solutions, electrolytes74 Ion standards (traceable to NIST) Ion standard Order number KBr ion standard (250 mL, c(Ion) = 0.1000 ± 0.0005 mol/L) 6.2301.000 NaCl ion standard (250 mL, c(Ion) = 0.1000 ± 0.0005 mol/L) 6.2301.010 Cu(NO3)2 ion standard (250 mL, c(Ion) = 0.1000 ± 0.0005 mol/L) 6.2301.020 NaF ion standard (250 mL, c(Ion) = 0.1000 ± 0.0005 mol/L) 6.2301.030 KI ion standard (250 mL, c(Ion) = 0.1000 ± 0.0005 mol/L) 6.2301.040 KCl ion standard (250 mL, c(Ion) = 0.1000 ± 0.0005 mol/L) 6.2301.060 CaCl2 ion standard (250 mL, c(Ion) = 0.1000 ± 0.0005 mol/L) 6.2301.070 KNO3 ion standard (250 mL, c(Ion) = 0.1000 ± 0.0005 mol/L) 6.2301.080 Pb ion standard (50 mL, c(Ion) = 1.000 g/L) 6.2301.100 Conductivity standard = 100 μS/cm (25 °C), for USP <645> and EP 2.2.38 (250 ml) 6.2324.010 with DKD certificate Conductivity standard = 100 μS/cm (25 °C), for USP <645> and EP 2.2.38 (5 x 30 ml in sachets) 6.2324.110 with DKD certificate Conductivity standard = 12.87 mS/cm (25 °C) (250 ml) 6.2301.060 Buffer and calibration solutions (traceable to NIST) Article Order number Buffer set (50 mL each of concentrate pH = 4.00, pH = 7.00, KCl solution 3 mol/L) 6.2302.010 Buffer set (50 mL each of concentrate pH = 4.00, 7.00, 9.00) 6.2304.000 Buffer set pH = 4.00 (3 x 50 mL of concentrate) 6.2305.010 Buffer set pH = 7.00 (3 x 50 mL of concentrate) 6.2305.020 Buffer set pH = 9.00 (3 x 50 mL of concentrate) 6.2305.030 Redox standard (250 mL, yields with reference electrode Ag/AgCl/c(KCl) = 3 mol/L 6.2306.020 U = + 250 ± 5 mV (20 °C); can also be used as buffer pH = 7) Ready-to-use buffer solution pH = 4.00 (500 mL), colored, with paper seal 6.2307.100 Ready-to-use buffer solution pH = 7.00 (500 mL), colored, with paper seal 6.2307.110 Ready-to-use buffer solution pH = 9.00 (500 mL), colorless, with paper seal 6.2307.120 Ready-to-use buffer solution pH = 4.00 (30 x 30 mL, in sachets), with DKD certificate 6.2307.200 Ready-to-use buffer solution pH = 7.00 (30 x 30 mL, in sachets), with DKD certificate 6.2307.210 Ready-to-use buffer solution pH = 9.00 (30 x 30 mL, in sachets), with DKD certificate 6.2307.220 Ready-to-use buffer solutions pH = 4.00, 7.00, 9.00 (each 10 x 30 mL, in sachets), 6.2307.230 with DKD certificate
  • 75. Electrolytes, storage solution, pHit kit 75Article Order numberElectrolyte solution c(KCl) = sat., 250 mL (storage of gel electrodes) 6.2308.000Electrolyte solution c(KCl) = 3 mol/L, 250 mL (for Ag/AgCl reference systems) 6.2308.020KCI solution saturated, thickened, 250 mL 6.2308.030Idrolyte, 250 mL (for 6.0224.100 Biotrode or for pH measurement > 80 °C with Unitrode) 6.2308.040Electrolyte solution c(KNO3 ) = 1 mol/L , 250 mL (reference electrolyte for combined Ag electrode 6.2310.010and bridge electrolyte for Ag/AgCl reference systems)Electrolyte solution (non-aqueous), LiClsat in ethanol, 250 mL (bridge electrolyte for Contact yourtitrations in non-aqueous solutions and reference electrolyte for Solvotrode 6.0229.100) Metrohm representativeElectrolyte solution (non-aqueous), c(LiCl) = 2 mol/L in ethanol, 250 mL (bridge electrolyte Contact yourfor titrations in non-aqueous solutions and reference electrolyte for Solvotrode 6.0229.100) Metrohm representativeElectrolyte solution c(KCl) = 3 mol/L, 1000 mL (for Ag/AgCl reference systems) 6.2313.000Electrolyte for NH3 electrodes, 50 mL (internal electrolyte for electrode 6.0506.100) 6.2316.030Porolyte, 50 mL (for 6.0235.200 Porotrode) 6.2318.000Electrolyte solution (non-aqueous), c(tetraethylammonium bromide) = 0.4 mol/L in ethylene glycol, 6.2320.000250 mL (bridge electrolyte for titrations in non-aqueous solutions and reference electrolytefor 6.0229.100 Solvotrode)Storage solution for combined pH glass electrodes with reference electrolyte c(KCl) = 3 mol/L 6.2323.000pHit Kit – Care kit for electrodes, containing 50 mL each of cleaning solution, KCl solution 6.2325.000c(KCl) = 3 mol/L, Storage solution and 2 storage vesselsElectrolyte KCL Gel c(KCl) = 3 mol/L, 50 ml (only as external electrolyte VA reference electrodes, 6.2308.060e.g. 6.0728.040) Illustrations reduced in size
  • 76. Electrical connections76 Connection of pH electrodes, ion-selective electrodes (ISE) and metal electrodes with Metrohm plug- in head G on Metrohm instruments Electrode Cable Order number Measuring device plug-in head Plug-in head G – plug F, 1 m 6.2104.020 For pH/ISE and Ind measuring inputs of Titroprocessors, Plug-in head G Plug-in head G – plug F, 2 m 6.2104.030 Titrinos and Titrandos, pH-/ ion meter ≥ 691 Plug-in head G – plug F, 3 m 6.2104.040 Plug-in head G – plug E (DIN 19262), 1 m 6.2104.050 For Metrohm pH Meter < 691 Plug-in head G – plug E (DIN 19262), 2 m 6.2104.060 Plug-in head G – plug E (DIN 19262), 3 m 6.2104.070 Electrode cables for generator electrodes 6.2104.120 KF Coulometer 6.0342.110, 6.0344.100 and 6.0345.100 pH electrodes with Adapter plug B (2 mm)/4 mm 6.2103.150 Titrinos (Pt 1000 only) fixed cable, plug B pH Meter ≤ 744 (2 mm) (Pt 1000 only) pH electrodes with Adapter plug B (4 mm)/2 mm (red) 6.2103.130 780/781/Titrandos fixed cable plug B Adapter plug B (4 mm)/2 mm (black) 6.2103.140 Pt 1000 (4 mm) (2 mm) Plug-in head U Plug-in head U – plug F + 2 x B (2 mm), 1 m 6.2104.600 Plug-in head U – plug F + 2 x B (2 mm), 2 m 6.2104.610 Connection of conductivity measuring cells and temperature sensors with plug-in head G to Metrohm instruments Electrode Cable Order number Measuring device plug-in head Plug-in head G – plug 2 x B (4 mm), 1 m 6.2104.080 712 Conductometer, measuring inputs Pt 100/ Plug-in head G Pt 1000 (4 mm) Plug-in head G – plug 2 x B (4 mm), 2 m 6.2104.110 Plug-in head G – plug 2 x 2 mm, 1 m 6.2104.140 780/781/Titrandos Pt 1000 Plug-in head G – plug 2 x 2 mm, 2 m 6.2104.150 (2 mm)
  • 77. Connection of reference electrodes and separate metal electrodes on Metrohm devices 77Electrode Cable Order number Measuring deviceplug-in head Plug-in head G – plug F, 1 m 6.2104.020 For «Ind II» measuring inputsPlug-in head G of Titroprocessors and Titrinos(6.0729.XXX) Plug-in head G – plug F, 2 m 6.2104.030 and for connection to a Metrohm differential Plug-in head G – plug F, 3 m 6.2104.040 amplifierPlug-in head B Plug-in head B (4 mm) – plug B 6.2106.020 For measuring input «Ref.» (4 mm), 1 m Plug-in head B (4 mm) – plug B 6.2106.060 (4 mm), 2 m Plug-in head B (4 mm) – plug B 6.2106.050 (4 mm), 3 mConnection of Metrohm electrodes with plug-in head G to devices made by other manufacturersElectrode Cable Order number Measuring deviceplug-in head Plug-in head G – BNC plug, 1 m 6.2104.090 Orion, Beckman, Corning,Plug-in head G EDT, Fisher, Hanna, Mettler- Toledo, Jenway, Philips Plug-in head G – LEMO 6.2104.160 Mettler Plug-in head G – plug E (DIN 19262), 1 m 6.2104.050 Older Metrohm devices, WTW, Knick, Schott Illustrations reduced in size Plug-in head G – Radiometer plug, 1 m 6.2104.130 Radiometer, Crison Plug-in head G – US plug, 1 m 6.2104.010 Older Orion, Beckman and Fisher devices
  • 78. How is a Metrosensor made?78 Our accuracy is not accidental ... Always keep cool! Many years of experience and a steady hand with raw materials guarantee that our chemistry is always correct. The right composition of the glass mixture and the great- est possible care during the melting process ensure the perfect quality of the membrane glass. We know how to do it! Our employees need the right feeling when fusing the membrane glass with the electrode body. That this is not just a matter of luck can be seen from our electrodes at the first glance..
  • 79. Our employees are only human!In some manufacturing processes, such as grinding our 79fixed ground-joint diaphragms, even a practiced eye nolonger stands a chance. Such tasks are carried out withunrivalled accuracy by the most modern machines.Tried and tested electrodes!Before our electrodes leave our premises they are sub-jected to a further wet-chemistry computer-supportedcheck. At its conclusion we provide a written confirma-tion so that you can have complete confidence in ourelectrodes: each electrode is supplied with its own testcertificate.Certificate of origin:Precision and guaranteed reliability – Metrohm stands forthe highest quality in ion analysis. Just convince your-self!
  • 80. 1. Basics of potentiometry80 1.1. Electrode construction In potentiometry the measuring setup always consists of Redox electrode two electrodes: the measuring electrode, also known as the indicator electrode, and the reference electrode. Both electrodes are half-cells. When placed in a solution together they produce a certain potential. Depending on the construction of the half-cells, the potential produced is the sum of several individual potentials. Potential- determining transitions always occur at the phase bound- aries, e.g. between the solution and the electrode surface. Figure 2: Schematic diagram of a redox electrode pH electrode Measuring electrode – metal electrode (left) U1 = redox potential between measuring solution and metal surface Reference electrode – silver/silver chloride (right) U4 = Galvani potential of reference electrode U5 = Diaphragm potential (diffusion potential) aM = Activity of measured ion in sample solution For metal electrodes the potential forming transitions U2 Figure 1: Schematic diagram of a pH electrode and U3 of the pH electrodes do not exist. Depending on the particular application, it may be possible to use a pH Measuring electrode – glass electrode (left) glass electrode as the reference electrode instead of the U1 = Galvani potential between measuring solution silver/silver chloride reference electrode. In the combined and glass membrane redox electrodes and Titrodes from Metrohm the half- U2 = Galvani potential between glass membrane cells are also contained in a single electrode. and inner electrolyte U3 = Galvani potential between inner electrolyte 1.2. From the measured potential to and inner reference electrode the ion concentration As each ion is surrounded by ions with the opposite Reference electrode – silver/silver chloride (right) charge, it is – to put it simply – no longer as effective as U4 = Galvani potential of reference electrode a free ion (see Debye-Hückel law). This affects both the U5 = Diaphragm potential (diffusion potential) reactivity and the size of the potentials at the measuring aM = Activity of measured ion in sample solution electrode. The activity of the measuring ion aM, which is also used in the Nernst equation, is linked to the normally The potentials U2, U3 and U4 can be kept constant by a interesting analytical concentration cM via the activity suitable electrode construction. Constructive measures coefficient : and the selection of a suitable reference electrolyte ensure that U5 is also kept as constant as possible. Ideally aM = * cM the measured potential should depend only on the potential between the glass membrane and the solution. (1) For practical reasons the half-cells of the measuring elec- trode and the reference electrode are normally contained in a single electrode; this is then known as a combined pH electrode.
  • 81. For dilute solutions with concentration cM ≤0.001 mol/Lthe activity coefficient tends towards 1 and the activity the temperature (see Equation 3). This is why it is abso- lutely necessary to take the temperature into account in 81of the ion corresponds to its concentration as a first all direct potentiometric measurements, as otherwise noapproximation. is a function of the total electrolyte correct results will be obtained.content. pH valueThe mathematical relationship between the activity aM of In practice – particularly when measuring the acid/ basea measuring ion in solution ions and the potential meas- equilibrium – the term pH, introduced by Sörensen inured between the reference electrode and the measuring 1909, is frequently used instead of the activity of theelectrode is described by the Nernst equation. This measuring ion aM:applies only for the (ideal) case in which an electrodeonly responds to a single type of ion. Potentials U2 to U5 pH = -log aH+for pH electrodes and U4 and U5 for redox electrodes,which are normally constant, appear as potential U0 in (Definition of the pH value) (4)the Nernst equation. The pH value is the negative common logarithm of the 2.303 * R * T U = U0 + * log aM hydrogen ion activity of a solution. The term p is fre- z*F quently used for the simplified presentation of very large(Nernst equation) (2) or small values. In a similar way pNa+ can be used for the activity of sodium ion, or pKA as acid constant or pKB asU = measured potential base constant for reaction constants. In each of theseU0 = temperature-dependent standard potential cases what is meant is the negative common logarithm of electrode of the particular value. If this definition is inserted in theR = general gas constant 8.315 J mol-1 K-1 Nernst equation then we obtain for the measuredT = temperature in Kelvin potential U:z = ionic charge including signF = Faraday constant 96485.3 C mol-1 U = U0 – 2.303 * R * T * pH z*FThe term in the Nernst equation in front of the logarithm (pH value and potential) (5)is known as the Nernst potential UN (also Nernst slope). Redox potentials (metal electrodes) UN = 2.303 * R * T In a similar way to the Nernst equation (Equation 2) the z*F equation for the activity-dependent potential is obtained(Nernst potential) (3) as follows:Under standard conditions (T = 298.15 K and z = +1) its 2.303 * R * T log aox * aH+ U = U0 + * aredvalue is 0.059 V. As a factor in the Nernst equation it z*Frepresents the theoretical electrode slope. UN corre- (6)sponds exactly to the alteration in potential caused byincreasing the activity aM by a factor of ten. From the Equation 6 usually allows the potential generated by aequation it can be seen that the electrode slope for redox pair at the measuring electrode to be calculated.electrodes that respond to ions with a double charge (z As protons are involved in most redox reactions, the= 2) is only half the size of that for electrodes for ions measured potential depends on the pH. If proton react-with a single charge (z = 1). In addition, the sign for ions cannot be excluded then the pH should also becation- and anion-sensitive measuring electrodes is determined or adjusted to a defined value.different, as z also takes the charge on the ion intoaccount. The Nernst potential is directly dependent on
  • 82. 82 1.3. Measuring electrodes 1.3.1. pH glass electrodes why conditioning the electrode in a suitable electrolyte is absolutely necessary to ensure an initial solvated layer How does a pH glass electrode work? condition that is as stationary as possible so that results The glass membrane of a pH glass electrode consists of can be obtained that are as reproducible as possible. a silicate framework containing lithium ions. When a glass surface is immersed in an aqueous solution then a thin solvated layer (gel layer) is formed on the glass sur- face in which the glass structure is softer. This applies to both the outside and inside of the glass membrane. As the proton concentration in the inner buffer of the electrode is constant (pH = 7), a stationary condition is established on the inner surface of the glass membrane. In contrast, if the proton concentration in the measuring solution changes then ion exchange will occur in the outer solvated layer and cause an alteration in the poten- tial at the glass membrane. Only when this ion exchange has achieved a stable condition will the potential of the Figure 3: The silicate skeleton of the glass membrane contains glass electrode also be constant. This means that the lithium ions, among other things. During the formation of the response time of a glass electrode always depends on solvated layer at the glass surface these are partly replaced by the thickness of the solvated layer. Continuous contact protons. If the concentration of the protons in the solution changes then a new stationary condition must again be with aqueous solutions causes the thickness of the sol- achieved in the solvated layer; this results in a change in vated layer to increase continuously – even if only very potential at the glass membrane. slowly – which results in longer response times. This is Table 1: Overview of the different electrode membrane glasses used by Metrohm Ltd Application U glass T glass M glass Aquatrode glass E glass (green) (blue) (colorless) (colorless) (yellow) pH range 0...14 0...14 0...14 0...13 0...13 Temperature range 0...80 °C 0...80 °C 0...60 °C 0...80 °C 0...80 °C continuous 0...100 °C short-term Membrane Electrodes with Electrodes with Electrodes with Large surfaces Electrodes with surface large membrane medium to large small membrane medium to large surface membrane surface (micro- membrane surface (mini- electrodes) surface electrodes) Special features For strongly Measurements in Measurements in Responds very Quick response, alkaline solutions, non-aqueous small-volume quickly, so excellent stability long-term meas- sample solutions samples particularly suitable in continuous use urements and for measurements measurements at in ion-deficient or high temperatures weakly buffered solutions Membrane resist- < 500 < 150 < 120 < 250 < 250 ance (MΩ) With reference to sphere membrane 10.5 mm diameter
  • 83. Why are there different types of glass forpH electrodes? 83Different demands are placed on a pH glass electrodedepending on the particular application. Various proper-ties such as response time, thermal resistance, chemicalstability, shape, size and electrical properties must all betaken into account in order to have an optimal electrodeavailable to solve each problem. In order to be able to dojustice to the numerous applications, different glasses areavailable with different properties (see table 1).Why must a pH glass electrode be calibrated? Figure 5: In the second calibration step with another buffer solution the electrode slope is determined and expressed as aThe potential of a measuring electrode can always only percentage of the theoretical value of 0.059 V (at 25 °C).be given relative to that of a reference electrode. To beable to compare systems, the electrode zero point isdefined as being 0 mV for pH = 7 and 298.15 K or 25 °C. The electrode zero point is set first (pH = 7 correspondingThe electrode slope, i.e. the alteration in the measured to 0 mV for Metrosensor pH electrodes). The second andvalue with the pH, is given by the Nernst equation and at further buffer solutions are used to determine the slope25 °C is 0.059 V per DpH = 1. These are ideal values from of the pH electrode. This slope is expressed as a percent-which Metrosensor electrodes only differ slightly. The age of the theoretical value (100% = 0.059 V per DpH =electrode zero point is ±0.015 V. The electrode zero point 1 at 25 °C). In order to minimize subsequent measuringand the electrode slope may change as a result of the errors, care should be taken that the expected measuredaging of the glass membrane or changes, (e.g contami- value of the sample solution always lies within the pHnation) on the diaphragm. For this reason the pH meter range covered by the buffer solutions. Modern pH andmust be adapted to the characteristics of the electrode, ion meters such as the 780 pH Meter and the 781 andi.e. calibrated, at regular intervals by using buffer solu- 867 pH/Ion Meter do not require any manual settings totions. be made. The buffer solutions are recognized automati- cally and can be presented in any sequence. Calibration always includes a check of the measuring electrode. The calibration buffers have a medium acid- base concentration and their ionic strength is approxi- mately that of the most common sample solutions. The dependency of the electrode slope on the temperature means that the calibration and measuring temperatures must be known. Information about the electrode condi- tion is provided by the electrode slope, electrode zero point, response time of the signal and its streaming dependency. With the Metrohm 781 and 867 pH/Ion Meter and 780 pH Meter an automatic electrode test can be carried out; this provides an exact statement of the electrode condition and often allows a source of error to be localized.Figure 4: In the first calibration step with buffer pH = 7the variation from the electrode zero point (= asymmetrypotential) is determined and corrected.
  • 84. 84 pH and temperature – an inseparable couple! The temperature has a considerable influence on the pH value and the pH measurement. If an electrode is cali- brated at 25 °C then it should be capable of linear meas- urement throughout the whole pH range and provide correct results. However, if the electrode is then used at a different temperature the electrode slope will change – in accordance with the Nernst equation – and possibly the electrode zero point as well. The point at which the two calibration curves (without correction) for different temperatures intersect is known as the isothermal inter- Figure 6: Isothermal intersection point section point. Thanks to the optimized inner buffer and «Long Life» reference system precise measurements can pH compensation will be incorrect as the temperature be made with Metrosensor pH electrodes at different and pH are not measured at the same location. In temperatures. This means that, although calibration is modern pH electrodes the temperature sensor should be only carried out at a single temperature, measurements located within the electrode in the immediate vicinity of can then be made throughout the whole temperature the glass membrane. This is the only way in which an range. The real behavior of Metrosensor pH electrodes accurate pH measurement is possible. If the sensor is varies from the ideal behavior by maximum ±15 mV. located outside the membrane then problems when Nevertheless it is still true that the accuracy of the meas- cleaning the electrode could easily occur. urement is increased when the electrode is calibrated at the temperature to be used for the subsequent measure- ments. Under standard conditions (z = 1, T = 298.15 K) Table 2: Dependency of the Nernst potential UN on the the Nernst potential UN is equal to 59.16 mV. For other temperature temperatures it can be corrected in the Nernst equation Temperature Slope UN Temperature Slope UN by using Table 2. Modern pH meters automatically take T (°C) (mV) T (°C) (mV) the temperature dependency of the Nernst potential into 0 54.20 50 64.12 account if a temperature sensor is connected. In princi- 5 55.19 55 65.11 ple, within the context of GLP/ISO recording and docu- 10 56.18 60 66.10 mentation of the temperature is required for all measure- 15 57.17 65 67.09 20 58.16 70 68.08 ments. 25 59.16 75 69.07 30 60.15 80 70.07 However, it must be remembered that a pH meter can 35 61.14 85 71.06 only correct the temperature behavior of the electrode 37 61.54 90 72.05 and never that of the solution to be measured. For cor- 40 62.13 95 73.04 rect pH measurements it is essential that the pH is meas- 45 63.12 100 74.03 ured at the temperature at which the sample was taken. For example, sodium hydroxide c(NaOH) = 0.001 mol/L at 0 °C has a pH of 11.94, at 50 °C it is pH = 10.26 and How to store a pH glass electrode? only at 25 °C is it pH = 11.00. This change in pH is caused The swelling of the glass surface is indispensable for the by the dependency of the ionic product of water on the use of glass as membrane for pH glass electrodes; with- temperature. out this solvated layer, no pH measurement would be possible. Glasses for pH glass electrodes are optimized in In some conventional electrodes the temperature sensor such a way that only protons can penetrate into the glass is not located in the immediate vicinity of the membrane, membrane. However, because of the very slow but i.e. in the electrode foot. This means that it cannot meas- steady swelling of the glass, it is unavoidable that also ure the temperature of the solution correctly and that the other ions penetrate into the glass, e.g. sodium and
  • 85. potassium ions. At higher concentrations, these lead tothe so-called alkali error of the glass electrode. This 85means that the measured value is falsified at compara-tively low proton concentrations. If the glass electrode isstored for a very long time in a strong solution of potas-sium or sodium, this leads to prolonged response timesof the glass membrane since the protons must expulsethe «added ions» from the solvated layer.One of the most used electrolytes for pH measurement is Figure 8: pH measurement in c(NaHCO3) = 0.05 mmol/L. Ac(KCl) = 3 mol/L, since the aequitransferent KCl causes glass of the Aquatrode stored in the storage solution shows aonly a very small diffusion potential at the diaphragm substantially shorter response time than an electrode glass of the same type stored during the same period in KCl.and is also economical. Normally a combined pH glasselectrode is stored in c(KCl) = 3 mol/L only for this reason,as one wants to have it ready for immediate use without the glass membrane remains unchanged regardingconditioning the diaphragm. However, on a long-term response time and alkali error. Moreover, if one usesbasis the storage in KCl affects the glass, since it leads to c(KCl) = 3 mol/L as the reference electrolyte, the opti-ever longer response times. For the membrane glass, mized composition of the storage solution keeps the pHstorage in distilled water would be optimal, but then the glass electrode ready for measurement. Conditioningdiaphragm would have to be conditioned for several before the measurement is not necessary, no matter forhours. The patented storage solution for combined pH how long the electrode has been stored.glass electrodes (6.2323.000) solves exactly this problem.If a combined pH glass electrode is kept in this solution,Table 3: The correct storage of pH glass electrodes Electrode resp. reference electrolyte Storage Separate pH glass electrode Distilled water Combined pH glass electrode with c(KCl) = 3 mol/L, 6.2323.000 Storage solution Porolyte Combined pH glass electrode with another In the respective reference electrolyte reference electrolyte (Idrolyte, non aqueous) Gel (spearhead electrode), Ecotrode Gel 6.2308.000 Electrolyte solution c(KCl) = sat. Troubleshooting The cause of most problems is not to be found in the measuring electrode and its glass membrane, but rather in the reference electrode, as much more critical dia- phragm problems can occur there. To avoid incorrect measurements and to increase the working life, attention must still be paid to the following possible sources of error:Figure 7: Cross-section of a pH glass membrane. If several kindsof cations are present in the measuring solution, these competefor the free spaces in the solvated layer. Especially potassiumand sodium can penetrate into the glass membrane and pro-long the response time.
  • 86. 86 Table 4: Possible sources of error and their remedies for pH glass electrodes Source of error Effects Action Alternatives HF-containing solutions Etching and dissolution Use of the Sb electrode of the glass membrane g corrosion potential during the measurement/short working life High pH value and high Increased alkali error g Use of electrodes with U alkali content pH too low glass High temperatures Rapid rise in membrane Use of electrodes with U resistance by aging g glass increased polarizability and drift Measurements at High membrane resistance Use of electrodes with low temperature g polarization effects T glass and Idrolyte as reference electrolyte Dry storage Zero point drift Store in water overnight Store in storage solution 6.2323.000 or reference electrolyte Reaction of a solution Slow response, zero point Try other glass types component with the glass shift, slope reduction Non-aqueous media Reduced sensitivity Store in water T glass/non-aqueous electrolyte solution Deposition of solids on Slow response, zero point Solvent or strong acids membrane surface shift, slope reduction Electrostatic charging Slow response No dab-drying of the Grounding of measuring electrode instrument Deposition of proteins on Slow response, zero point 5% pepsin in 0.1 mol/L membrane surface shift, slope reduction HCl Possible sources of error and care information for diaphragm problems are given in Section 1.4. for reference electrodes. 1.3.2. Metal electrodes How does a metal electrode work? Metal electrodes have an exposed metal surface. If ions This concentration-dependent equilibrium is character- of this metal are contained in the sample solution then ized by a corresponding potential E0 (Galvani potential), an equilibrium is formed at the metal surface that e.g. the Ag/Ag+ equilibrium at a silver surface has a value depends on the concentration of the metal ions in the of E0 = 0.7999 V (25°C). If the sample solution does not solution (see «Theory of the electrical double layer» in contain any ions of the corresponding metal then metal electrochemistry textbooks). Metal ions are accepted by electrodes can still form a Galvani potential if a redox the metal surface and simultaneously released into the reaction occurs in the sample solution. solution. n+ – 0 Sox + n * e– Sred Me Me +n * e E =... (9) (8)
  • 87. The electrode surface is inert to the redox reaction. Nometal ions are released from the metal; in this case the In the literature the so-called standard redox potentials E0 can usually be found. 87metal surface only acts as a catalyst for the electrons. Asgold and platinum electrodes are to a large extent Cl2 (g) + 2e– → 2 Cl– E0 = + 1.359 Vchemically inert, they are used for the measurement of Fe3+ + e– → Fe2+ E0 = + 0.771 Vredox potentials. Silver electrodes are only used as indi- Cd2+ + 2e– → Cd2– E0 = – 0.403 Vcator electrodes for titrations. The zero point of these systems is defined (arbitrarily)Calibrating a metal electrode with the standard hydrogen electrode (SHE) which isRedox-buffer solutions (6.2306.020) are used for quickly assigned a standard potential of 0 mV. If electrons arechecking metal or redox electrodes. As the potential released by a redox system to the SHE then this ismeasured in a redox buffer solution is insensitive to the reduced and the redox pair receives a negative sign; ifelectrode’s surface condition, contamination of the electrons are accepted then the SHE is oxidized and themetal electrode is often not recognized. For this reason result is a redox potential with a positive sign. The stand-redox-buffer solutions are rather more suitable for check- ard hydrogen reference electrode is difficult to handle.ing the reference electrode. If the potential is displaced The specifications of the SHE stipulate that a platinizedthen the metal electrode is contaminated, the redox platinum wire must be used; this is located in a stream ofbuffer partly oxidized or the functioning of the reference hydrogen gas at a partial hydrogen pressure of 1.0 bar,electrode is affected. Under no circumstances should the and that the activity of the hydrogen ions in the solutionindicated potential be set to the theoretical value. in which the platinized platinum wire is immersed is to be exactly 1.00 mol/L. The normal alternative is the Ag/If measurements are made in weakly redox-buffered AgCl/KCl reference electrode, which has a potential E0 =solutions then a suitable pretreatment of the metal +207.6 mV at c(KCl) = 3 mol/L and T = 25 °C. Theelectrode is recommended to adapt the surface condi- Metrohm redox standard (6.2306.020) can be used fortion as much as possible to the measurement conditions checking separate and combined metal electrodes.(abrasive pretreatment: carefully clean the electrode with Platinum and gold electrodes together with the Ag/AgCl/abrasive paste). The reference electrode can either be KCl reference electrode (c(KCl) = 3 mol/L and T = 20 °C)checked against a second reference electrode that has produce a potential of +250 ± 5 mV.already been checked in buffer solutions 4 and 7(response behavior and reference potential) or by usingthe redox buffer.Table 5: Measuring data for 6.2306.020 redox standard as a function of the temperatureTemp. (°C) 10 20 25 30 40 50 60 70mV ± 5 + 265 + 250 + 243 + 236 + 221 + 207 + 183 + 178pH ± 0.05 7.06 7.02 7.00 6.99 6.98 6.97 6.97 6.98If instead of an Ag/AgCl/KCl reference electrode c(KCl) = from Metrohm, the correction to be applied is -37 mV.3 mol/L an Ag/AgCl/KCl reference electrode c(KCl) = sat. The Titrodes are checked by a standard titration as nois used for the measurement then at 25 °C a correction suitable calibration or buffer solutions are available. Forof +10 mV must be applied; if the measurement is made example, the certified ion standard c(NaCl) = 0.1 mol/Lusing an Hg/Hg2Cl2/KCl calomel reference electrode, (6.2301.010) can be titrated with a silver nitrate standardwhich for toxicological reasons is no longer available solution.
  • 88. 88 Troubleshooting Table 6: Problems encountered when measuring with metal electrodes Electrode Source of error Effects Cleaning Alternatives Ag Electrode poisons Passivation of Ag layer g Cleaning with abrasives such as S2–, I–, Br– slow response Pt/Au Fats or oils Isolating layer g slow Cleaning with solvent response, incorrect potential Weakly redox- Adsorbed ions on the Abrasive, oxidative (for Use of Au or Pt buffered solution surface (e.g. oxides) g oxidizing solutions) or slow response reducing (for reducing solu- tions) pretreatment COD determination Deactivation of Pt Use of Au 1.3.3. Ion-selective electrodes best-known examples of such a cross-sensitivity is the How does an ion-selective electrode work? so-called alkali error of pH glass electrodes. With some An ion-selective electrode (ISE) can selectively recognize types of glass the linear range does not extend through- an ion in a mixture of ions in a solution. There are various out the whole pH range from 0 to 14 and at high pH types of ion-selective electrodes, the most commonly values a departure from linear behavior can be observed. used ones are: The reason for this is that at very low H+-concentrations any alkali ions present in the solution (possibly released Glass membrane framework of silicate glass from the walls of the vessel) will falsify the measured with interstitial sites for H+ and Na+ value. Unfortunately there are only a very few ion-selec- tive electrodes that have a linear range similar to that of Crystal membrane crystal lattice containing defined pH glass electrodes. The use of an ISE is normally restrict- gaps for the ion to be measured ed to a concentration range of 6 to 8 powers of ten. If an ISE is used for a measurement right at the limit of the Polymer membrane polymer membrane containing a linear range then the Nernst equation (Eq. (5), Section molecule (= ionophore) that only 1.2.) must be extended by the contribution made by the binds the ion to be measured particular interfering ion for the evaluation of the meas- ured potential: In contrast to metal electrodes, an ISE does not measure 2.303 * R * T log (a +K a ) a redox potential. If the ion to be measured is contained U = U0 + * M S* S in the sample solution then this ion can penetrate the z*F membrane. This alters the electrochemical properties of (Nikolsky equation) (10) the membrane and causes a change in potential. One hundred percent selectivity for exactly one type of ion is KS is the so-called selectivity coefficient of the ion-selec- only possible on rare occasions. Most ion-selective elec- tive electrode for interfering ion S. This is a factor that trodes have «only» a particular sensitivity for a special describes the influence of the interfering ion in relation- type of ion, but also often react with ions with similar ship to the ion to be measured. These selectivity coeffi- chemical properties or a similar structure (see Table 7). cients are known for the most important interfering ions This is why the cross-sensitivity to other ions that may be for an ISE and therefore a simple estimation can be made contained in the sample solution must always be taken as to whether an interfering ion contained in the sample into consideration when selecting an ISE. One of the solution will influence the measured value or not.
  • 89. Direct measurement or standard addition?The question often arises as to which determination Sample addition Similar to standard addition, with the difference that 89method is most suitable for a particular sample. In prin- defined volumes of the sample solution are added to aciple there are three different ways of carrying out an ion defined amount of an ion standard.measurement with ion-selective electrodes: Modern ion meters such as the 781 pH/Ion Meter fromDirect measurement Metrohm can carry out these addition methods auto-Direct measurement is chiefly of benefit with high sam- matically. The addition of the standard or sample solutionple throughputs or with a known sample solution of a is automatically controlled from the ion meter – by press-simple composition. The ion-selective electrode is cali- ing a single key – and evaluated by using the Nikolskybrated with special standard solutions of the ion to be equation.measured before the measurement itself in a similar wayto the calibration of a pH glass electrode and can then be ISA and TISAB – when and why?used for several determinations in series. The activity coefficient of an ion (Section 1.2.) is a func- tion of the total electrolyte content. For this reason careStandard addition must be taken that ion-selective measurements areStandard addition is recommended whenever a determi- always carried out in solutions with approximately thenation only needs to be carried out occasionally or when same ionic strength. In order to achieve this, the so-the composition of the sample is unknown. Defined vol- called ISA solutions (Ionic Strength Adjustor) or TISABumes of a standard solution of the ion to be measured solutions (Total Ionic Strength Adjustment Buffer) shouldare added to the sample solution in several steps. The be added to the sample solution (see Table 7). These areconcentration in the original solution can then be calcu- chemically inert and have such a high ionic strength thatlated from the initial potential and the individual poten- the ionic strength of the sample solution can betial steps after the addition of the standard. The advan- neglected after their addition.tage of standard addition is that the ISE is calibrateddirectly in the sample solution, which eliminates allmatrix effects.Table 7: Interfering ions and recommended ISA and TISAB solutions for ion-selective electrodesIon Membrane pH range1 ISA Most important Remarks 2 3 material or TISAB interfering ionsAg + Crystal 2...8 c(KNO3) = 1 mol/L Hg2+, Proteins 1) The given pH range onlyBr – Crystal 0...14 c(KNO3) = 1 mol/L Hg2+, Cl–, I–, S2–, CN– applies to ion-selective 2...12 electrodes from MetrohmCa2+ Polymer c(KCl) = 1 mol/L Pb2+, Fe2+, Zn2+, Cu2+, Mg2+ Ltd.Cd2+ Crystal 2...12 c(KNO3) = 1 mol/L Ag+, Hg2+, Cu2+Cl– Crystal 0...14 c(KNO3) = 1 mol/L Hg2+, Br–, I–, S2–, S2O32–, 2) Alternatives or more de- – CN tailed compositions can beCN– Crystal 10...14 c(NaOH) = 0.1 mol/L Cl , Br–, I–, – found in the manual «IonCu2+ Crystal 2...12 c(KNO3) = 1 mol/L Ag+, Hg2+, S2– Selective Electrodes (ISE)», 5...7 order number 8.109.1476F– Crystal NaCl/glacial acetic acid/ OH– CDTA 3) More detailed informa-I– Crystal 0...14 c(KNO3) = 1 mol/L Hg2+, S2–, S2O32–, tion about interfering ionsK + Polymer 2.5...11 c(NaCl) = 0.1…1 mol/L TRIS+, NH4+, Cs+, H+ and other interferencesNa+ Glass 5...9 C(TRIS) = 1 mol/L H+, Li+, K+, Ag+ can be found inNa+ Polymer 3...12 c(CaCl2) = 1 mol/L SCN–, K+, lipophilic ions the manual «Ion Selective 11 Electrodes (ISE)», orderNH4+ Gas membrane – – number 8.109.1476NO3– Polymer 2.5...11 c((NH4)2SO4) = 1 mol/L Cl–, Br–, NO2–, OAC–Pb2+ Crystal 4...7 c(NaClO4·H2O) = 1 mol/L Ag+, Hg2+, Cu2+S2– Crystal 2...12 c(NaOH) = 2 mol/L Hg2+, ProteinsSCN – Crystal 2...10 c(KNO3) = 1 mol/L Cl–, Br–, I–, S2–, S2O32–, CN–
  • 90. 90 Troubleshooting Table 8: Possible sources of interference and remedies for ion-selective electrodes Electrode Source of inter- Effects Action ference Ion-selective crystal Dissolution processes,Rough surface g slow response, Polish with polishing cloth membrane oxidation processes poor detection limits Electrode poisons Formation of more sparingly soluble Polish with polishing cloth, salts on the electrode surface than with mask interfering ion the ion to be measured g zero point shift, reduced linearity range Ion-selective Dissolution processes Diffusion into the membrane or Elimination of interfering polymer membrane dissolution of membrane component components NH3 sensor Volatile bases Electrolyte becomes contaminated g Change electrolyte (amines) displacement of calibration line, limited linearity Surfactants Membrane becomes wetted g Replace membrane slow response 1.4. Reference electrodes Reference electrodes are usually electrodes of the second bration purposes. Some titrations offer the possibility of kind. In this type of electrode a metal electrode is in using pH glass electrodes as reference electrodes. Even if contact with a sparingly soluble salt of the same metal. protons are transferred during the titration it is usually The potential depends only on the solubility of the salt. still possible to make an accurate determination of the As a first approximation, electrodes of the second kind endpoint. do not themselves react with the solution and therefore supply a constant potential. 1.4.1. Silver/silver chloride reference electrode The reference element of the silver/silver chloride refer- The most frequently used reference electrode is the sil- ence electrode is the silver/silver chloride/potassium ver/silver chloride reference electrode (Ag/AgCl/ KCl). The chloride solution system: Ag/AgCl/KCl. The reference calomel electrode (Hg/Hg2Cl2/KCl), which was formerly electrode is usually filled with c(KCl) = 3 mol/L or satu- widely used, is hardly used at all today as mercury and its rated KCl solution. Tables 9 and 10 show the potentials salts are extremely toxic and all the applications can also of the reference electrode as a function of the reference be carried out with the silver/ silver chloride reference electrolyte and temperature. Each of these values has electrode. The standard hydrogen electrode SHE is also been measured against the standard hydrogen electrode an electrode of the second kind. It is only used for cali- under isothermal conditions. Table 9: Standard redox potentials of the silver/silver chloride reference electrode as a function of the temperature and concentration Temp. (°C) 0 +10 +20 +25 +30 +40 +50 +60 +70 +80 +90 +95 E0 (mV) with +224.2 +217.4 +210.5 +207.0 +203.4 +196.1 +188.4 +180.3 +172.1 +163.1 +153.3 +148.1 c(KCl) = 3 mol/L E0 (mV) with +220.5 +211.5 +201.9 +197.0 +191.9 +181.4 +170.7 +159.8 +148.8 +137.8 +126.9 +121.5 c(KCl) = sat. Table 10: Standard redox potentials of the silver/silver chloride reference electrode as a function of the concentration c(KCl) / mol/L (25 °C) 0.1 1.0 3.0 3.5 sat. 0 E (mV) +291.6 +236.3 +207.0 +203.7 +197.0
  • 91. 1.4.2. The Metrosensor «Long Life» reference systemMost electrodes are equipped with the silver/silver chlo- year the concentration of silver chloride in the outer electrolyte has only reached 5% of the saturation value. 91ride reference system. The solubility product of silverchloride in water is very small (10-10 mol/L). In the con- The advantages of the «Long Life» reference systems at acentrated, chloride-containing solution of the reference glance:electrolyte soluble complexes of the series (AgCl2)-,(AgCl3)2-, (AgCl4)3- are formed. This means that the refer- Long working life of the electrodeence system poses several problems. Outside the elec- Rapid response to changes in pHtrode the chloride concentration is frequently lower and Rapid response to temperature changesthe complexed silver chloride precipitates in the region Less sensitive to electrode poissons, e.g. S2-surrounding the diaphragm («liquid junction»). The result:precipitated silver chloride blocks the diaphragm, the Blocking the diaphragm by crystallized AgCl also affectsresponse time of the pH electrode increases and with the electrolyte flow. If the «Long Life» reference system istime the electrode becomes inactive. A further problem used then the flow of the KCl solution through the dia-is presented by the dependency of the solubility product phragm into deionized water only decreases slightly.of AgCl on the temperature. If the electrode is used at adifferent temperature then the equilibrium that deter- As in the «Long Life» reference system the silver chloridemines the potential of the reference electrode must be is present in a smaller volume of potassium chloridereestablished. The larger the surface with solid AgCl in solution, the thermodynamic equilibrium between silver,relationship to the electrolyte volume, the shorter the silver chloride (solid) and silver chloride (dissolved) istime required. The «Long Life» reference system prevents established very quickly and the potential of the refer-high concentrations of complexed AgCl from occurring ence electrode becomes stable after a very short time.in the outer electrolyte, as the silver chloride reservoir isconnected with the outer electrolyte by a highly effective 1.4.3. Diaphragmsdiffusion barrier. The concentration of the silver complex Faulty measurements, unstable measured values and veryin the reference electrolyte remains low. Even after one long response times usually have their source in the «liquid junction» between the sample solution and the reference electrode. The diffusion, streaming and Donnan potentials that occur there – which are normally known Figure 9: together as the diaphragm potential – have various Conventional Ag/AgCl/ KCl system. The chloride causes and can result in a very incorrect measured value. concentration outside The measuring error may assume vast proportions if the electrode is usu- measurements are made under the following condi- ally lower than in the tions: electrolyte chamber. The soluble silver chloride with a blocked, virtually impermeable diaphragm, complexes precipitate in ion-deficient solutions with an unsuitable out in the region sur- diaphragm, rounding the in strong acids and bases with an unsuitable diaphragm and may block it. diaphragm, in colloidal solutions. Figure 10: The Metrohm «Long Life» reference system. The dissolved AgCl is retained in the AgCl cartridge and can no longer block the dia- phragm.
  • 92. 92 In all such cases errors may occur that cannot be toler- ated. This is why the following questions must be in the phragms tend to become blocked and therefore should not be used in solutions containing precipitates. An foreground whenever an electrode and therefore the important advance with regard to the prevention of dia- optimal type of diaphragm are to be selected: phragm blockages by silver chloride and silver sulfide has Does the reference electrolyte react with the sample been achieved by the introduction of the «Long Life» solution to form a precipitate in the diaphragm? reference system (see Section «The Metrosensor «Long Does the electrolyte flow alter the composition of the Life» reference system»). sample solution in an unacceptable way? Is there a risk of depositing sample solution compo- Ground-joint diaphragms with fixed or separable nents on the diaphragm? ground joint Is the chemical resistance assured? Ground-joint diaphragms with fixed or separable ground Can physical parameters such as flow, pressure or joint are used in ion-deficient media, among others, as temperature cause measuring errors? they produce a steady signal that is almost independent Does the process allow cleaning/maintenance of the of sample flow conditions. The risk of blockage by silver electrode at certain intervals? chloride or by precipitates formed in the sample solution Is a short response time and/or high reproducibility is relatively low because of the large surface area. necessary? Streaming potentials, which may occur in measurements in flowing or stirred solutions, remain negligibly small. The time required for cleaning and maintenance can These properties are particularly important for a SET titra- usually be considerably reduced if the correct choice of tion to a defined pH or potential value. For example: the electrode is made. The most frequent cause of measuring determination of the carbonate alkalinity by a SET titra- problems is contamination of the diaphragm. This is why tion to pH = 5.4 according to ISO 9963-2 is a widely used with pH electrodes the chief attention is paid to the method in the routine analysis of drinking water. During diaphragm during maintenance with the pH membrane a titration it is not possible to dispense with stirring, i.e. being of secondary importance. If existing means cannot with an incorrectly measured pH or potential at the start be used to determine whether the indicator electrode or of the titration an incorrect endpoint is the inevitable the reference electrode requires cleaning/regeneration, result. Figures 11 and 12 clearly show the difference then it is usually best to treat the reference electrode. between the Aquatrode Plus (6.0253.100), which was Various types of diaphragm are available to satisfy the specially developed for this application, and a conven- diverse requirements. These requirements have already tional pH glass electrode with ceramic pin diaphragm. been taken into consideration for the electrode recom- mendations in the application lists on pages 6 and 7. Ceramic pin diaphragms Ceramic pin diaphragms are frequently used diaphragms. They are primarily suitable for clear, aqueous sample solutions. They normally have pore diameters of up to 1 μm with a length and diameter each of about 1 mm. This results in an electrolyte flow rate of up to 25 μL/h, depending on the condition of the diaphragm. This means that the reference electrolyte only requires refilling at long intervals; this is why electrodes with ceramic pin diaphragms are particularly suitable for long-term meas- urements. On the other hand, because of their small pores and large polar surface (>>500 mm2), ceramic dia-
  • 93. The ring-shaped geometry and the small polar surface of the ground joint diaphragm have a favorable effect on 93 the measurement. The increased electrolyte flow influ- ences the sample solution more than if a ceramic pin diaphragm was to be used, the reference electrolyte normally needs refilling on a daily basis during long-term measurements. Capillary diaphragms In pH measurements in critical samples the very smallFigure 11: Measured pH of a solution with c(Na2CO3) = pores of conventional ceramic diaphragms are easily0.14 mmol/L. Even under vigorous stirring the Aquatrode Plus blocked. The concept that has been realized in thedeviates by only approx. 0.05 pH units (corresponding to ap- Porotrode (6.0235.100), with two capillaries and a flowprox. 3 mV) from the unstirred value, in contrast the pH glass rate of 15...25 μL/h ensures unhindered contact betweenelectrode with ceramic pin diaphragm deviates by approx. 0.2pH units. the reference electrolyte and the sample solution (liquid/ liquid phase boundary), while the two capillaries of the Porotrode are practically insensitive to contamination. The reference electrode is filled with Porolyte, which has been specially developed for this electrode. The constant flow of Porolyte ensures that the potential is established quickly and reproducibly. The flow rate and therefore the refilling intervals are comparable to those of conven- tional electrodes. Extra maintenance work is not neces- sary. Measurements in problematic samples can be carried out easily and reproducibly thanks to the concept that has been realized in the Porotrode. The pH of sam- ples containing protein, such as milk and beer, can nowFigure 12: Endpoint volumes of a SET titration of a solution be determined without any diaphragm problems. Inwith c(Na2CO3) = 0.14 mmol/L with the titrant c(H2SO4) = 0.035mol/L to pH 5.4. The endpoints of the Aquatrode Plus are virtu- contrast to traditional pH electrodes the Porotrode meas-ally independent of the stirring speed. At higher stirring speeds ures correctly even at high surfactant concentrations.the deviation from the theoretical value of the pH electrodewith ceramic diaphragm amounts to approx. 5%.Fixed ground-joint diaphragms have a uniform andreproducible electrolyte flow and are therefore particu-larly suitable for use with sample changers.Separable ground-joint diaphragms are easy to clean andtherefore particularly suitable for applications where con-tamination of the diaphragm cannot be prevented. Theelectrolyte flow may reach up to 100 μL/h and is nor-mally considerably higher than the amount of electrolyteflowing from a ceramic or fixed ground joint diaphragm.
  • 94. 94 Twin pore Measuring the pH in semi-solid samples such as cheese, long-term behavior: even when used in difficult media the electrode zero point retains its long-term stability. meat and fruit places special demands on an electrode. The use of polymer electrolytes means that refilling a Proteins, fats and carbohydrates and other semi-solid liquid reference electrolyte is no longer necessary. substances in foodstuffs tend to block the fine pores of the ceramic diaphragms used in most pH electrodes, as The new Ecotrode Gel electrodes (6.0221.x00) are such substances adhere extremely well to the fine-pore equipped with this diaphragm which keeps maintenance ceramic surface. With the development of the spearhead effort low. electrode (6.0226.100) and the polymer electrolytes this problem has been elegantly eliminated: two pinhole Plied platinum wire diaphragms take over the function of the «liquid junc- In combination with the reference electrolyte Idrolyte, tion» between the sample and the reference electrode. which contains glycerol, the plied-platinum-wire dia- The polymer electrolyte adjacent to the openings, which phragm is outstandingly suitable for applications in bio- is spiked with potassium chloride and thickened, is to a logical media. The precipitation of proteins is suppressed large extent insensitive to contamination by media con- by using an electrolyte with a low KCl content. The taining proteins and fats. This insensitivity to contamina- multi-capillary system (channels between the platinum tion, the efficient protection of the reference electrode wires) reduces contamination effects and the electrically against the penetration of electrode poisons and the conductive platinum reduces the response time and the optimized inner buffer of the measuring electrode ensure diaphragm resistance. However, cross-sensitivity may that the new spearhead electrode has an outstanding occur in strongly redox-buffered solutions. Cleaning and care of diaphragms Table 11: Recommended ways of cleaning diaphragms Type of diaphragm Type of contamination Cleaning General Preventiv and regular care 6.2325.000 pHit Kit according to instructions Precipitates of silver halides Immerse diaphragm for several hours in and silver sulfides a solution of 7% thiourea in 0.1 mol/L HCl. Proteins, polypeptides Immerse diaphragm for several hours in a solution of 5% pepsin in 0.1 mol/L HCl. Suspensions, solids, resins, Clean electrode with suitable solvent glues, oils, fats Fixed ground joint All types of contamination Aspirate off reference electrolyte and immerse electrode in the corresponding cleaning solution. Separable ground joint All types of contamination Loosen the ground-joint sleeve (using hot water if necessary) and clean according to the type of contamination. Capillary Electrolyte flow interrupted Apply slight counterpressure to electrolyte refilling opening
  • 95. 1.4.4. Reference electrolytes and bridge electrolytesThe reference or bridge electrolyte is in galvanic contact extent achieved by the use of c(KCl) = 3 mol/L. On the one hand the ionic mobilities of K+ and Cl– are practically 95with the sample solution via the diaphragm. The sample the same, on the other hand the ionic concentration insolution and electrolyte form a phase boundary with the sample solution is normally negligibly low in com-different ion concentrations on each side. This difference parison to c(KCl) = 3 mol/L. This is why the equal-trans-in concentration causes diffusion of the ions to the other ference KCl electrolyte is used as standard in all com-side and, because of the different ion mobilities, a bined Metrohm electrodes and reference electrodes.so-called diffusion potential occurs. In order to achieve a However, certain media require the use of other electro-high degree of measuring accuracy the electrolyte com- lyte compositions in order to suppress effects that occurposition must be selected so that any diffusion potentials in addition to the diffusion potential.formed are as negligible as possible; this is to a largeTable 12: Alternatives to the standard reference electrolyte c(KCl) = 3 mol/LMedium Problems with standard electrolytes Alternative electrolyte c(KCl) = 3 mol/L Reaction with Cl with precipitation of AgCl g slow –Silver ions 1 mol/L KNO3 (or Titrode for more response or less constant pH value)Non-aqueous Precipitation of KCl, solutions and electrolyte 2 mol/L LiCl in ethanol or LiCl immiscible g unsteady signal saturated in ethanolIon-deficient water Contamination of the medium by salt g drift KCl solution of lower concentrationProteins/polypeptides Precipitation of the proteins with KCl and AgCl g Idrolyte1 zero point shift/reduced slopeSemi-solid substances Contamination of diaphragm g zero point shift/slow Solid electrolyte in combination response with pinhole diaphragmSurfactants (proteins) Adsorption on diaphragm g zero point shift/ Porolyte2 reduced slope1 IIdrolyte is a glycerol-based electrolyte whose chloride ion activity corresponds to that of a KCl solution with c(KCl) = 3 mol/L. This means that the latter can also be readily replaced by Idrolyte. Idrolyte is excellent for use with solutions containing proteins and aqueous solutions with an organic fraction.2 Porolyte is a KCl solution that has been gelled by polymerization and is used in electrodes with a capillary diaphragm (Porotrode).Table 13: Electrolyte flow rates and viscosities Electrolyte Viscosity Flow rate μL/h (10 cm water column) (25 °C) Ceramic pin Flexible ground Fixed Ceramic Plied Pt (mPas) joint ground capillary wire joint c(KCl) = ~1 Standard electrode Ø 10 mm: 20...100 5...30 – – 3 mol/L 5...25 Microelectrode 5...15 Ø 5 mm: 5...30 c(KNO3) = ~1 10...25 Ø 10 mm: 20...100 – – – 1 mol/L Ø 5 mm: 5...30 Idrolyte 8...10 – – – – 3...25 Porolyte 1200...1500 – – – 5...30 –
  • 96. 2. Basics of conductometry96 2.1. General Conductometry means measuring the conductivity – a c = distance between Pt sheets [cm–1] conductometer measures the electrical conductivity of electrode surface area ionic solutions. This is done by applying an electric field between two electrodes. The ions wander in this field. Cell constant (11) The anions migrate to the anode and the cations to the cathode. In order to avoid substance conversions and the must be known. The result of the measurement is there- formation of diffusion layers at the electrodes (polariza- fore always given as the specific conductivity with the tion), work is carried out with alternating voltage. The unit Siemens per cm (S·cm–1). rule of thumb is that the frequency of the alternating voltage must be increased as the ion concentration L * c [S cm–1] increases. Modern conductometers automatically adapt the measuring frequency to the particular measuring Specific conductivity (12) conditions. This means that the conductometer must be calibrated Ion migration in an electric field depends on many fac- before each measurement by determining the cell con- tors. The temperature has a decisive influence on the stant in a solution of known specific conductivity. The viscosity of the solution and therefore on the mobility of specific conductivity for various concentrations of many the ions. As the temperature increases the viscosity salts is given in tables. The specific conductivity is decreases and the conductivity increases. Dissociation linked with the concentration ci of the individual ion i via constants are also temperature-dependent quantities. the concentration-dependent equivalent conductivity i. This is why it is important to make measurements at a The equivalent conductivity i is similar to the activity constant temperature or to compensate for changes of coefficient (see Section 1.2.) and is also a quantity that temperature by using the so-called temperature coeffi- depends on the concentration. cient. The temperature coefficient of most salt solutions ∑( is approx. 2%/°C, but depends on the temperature in i i * zi * ci) very dilute solutions. Specific conductivity and concentration (13) The measuring unit used in conductivity measurements is At great dilutions, i.e. ci ≤0.001 mol/L, the equivalent the electrical resistance of the solution. This means that conductivity i can be equated with the equivalent con- the conductivity is a sum parameter which includes all ductivity shown in the tables for an infinite dilution. dissolved ions. Conductivity cannot be used for the determination of a single type of ion, unless the sample is a solution of a single salt or the concentrations of the other ions are known. The reciprocal value of the meas- ured resistance of the solution, the so-called conduct- ance L with the unit Siemens (S = Ω-1) is by itself less meaningful, as the shape of the measuring cell must be taken into account. The cell constant c of a conducto- metric measuring cell
  • 97. Table 14: Conductivity of various substances and solutions –1 97Conductor T( ) Conductivity due to Conductivity (μS cm )Metallic copper 273 Electron conduction 645,000,000,000Potassium hydroxide 291 Ionic conduction resulting from the complete 184,000solution (c = 1 mol/L) dissociation of KOHKCl solution 293 Ionic conduction resulting from the complete 11,660(c = 0.1 mol/L) dissociation of KClBrackish water 273 Ionic conduction resulting from the dissociation of salts 20,000 to 1,000,000 and carbonic acidAcetic acid 291 Ionic conduction resulting from the partial dissociation 1300(c = 1 mol/L) of CH3CH2COOHDrinking water 298 Ionic conduction resulting from the dissociation of salts 10 to 2000 and carbonic acidGraphite 273 Electronic conduction 1200Distilled water 273 Ionic conduction resulting from contamination 0.06...10 by salts, dissociation of water and carbonic acidUltrapure water 273 Ionic conduction resulting from low self-dissociation 0.056Pure benzene 273 Ionic conduction resulting from the dissociation of 0.00000005 traces of waterConductometry is used for direct measurements and in Conductivity measurementstitration. The theory is identical for both methods. Whereas the instruments used for potentiometry haveWhereas in direct measurements it is the absolute value been standardized (input impedance >1012 Ω, zerothat is of interest, in titrations it is the change in the point at pH 7), this is not the case with conductometers.measured value. Direct measurement is often used for The influence of the cable capacity, the measuring fre-monitoring surface waters, waterworks, water desalina- quency level, the conductivity range and the adjustabletion plants and in the preparation of ultrapure water, cell constant, the method used for conductivity measure-where particular limits must not be exceeded. Conductivity ments (phase-sensitive, frequency-dependent, bipolardetection is mostly used for precipitation titrations, pulse, etc.) vary and depend on the type of instrument.where the equivalent point is recognized by the conduc- This means that the instrument must be taken intotivity reaching a minimum value. The absolute value is of account for solving application problems. Importantsecondary importance. parameters are: Platinizing quality (platinum black) g high series capacity CS Electrode area A g high series capacity CS Cell constant c Measuring frequency f Cable capacity CP Cable resistance RC Instrument measuring range (resistance range)
  • 98. 98 Selecting the right cell constant The cell constant c is defined for conductometric meas- Interferences, care Conductivity measuring cells with Pt sheets uring cells. A measuring cell with two parallel electrodes Conductivity cells have a very porous black platinum at a distance of 1 cm and each with an area of 1 cm2 coating in order to avoid polarization effects in media theoretically has a cell constant c = l · A-1 = 1 cm-1. The with a high conductivity. However, the properties of this cell constant is never exactly l · A-1, as the electric field is coating may change in time (contamination, abrasion of not strictly homogeneous. The rules of thumb given in the platinum coating, etc.); this could alter the cell con- Table 15 are used for selecting the correct measuring stant. This is why it is absolutely necessary to calibrate cell: the conductometric measuring cell before making a measurement in order to avoid measuring errors. For the exact determination of cells with a cell constant of <1 cm-1 a solution with a conductivity of about 100 mS/ cm is recommended. If measurements are made in well conducting media then a check of the activity of the platinum layer is additionally recommended, e.g. in a 0.1 mol/L KCl solution. If a lower specific conductivity is shown then cleaning with a suitable oxidizing agent or solvent is indicated. If measurements are made in ion-deficient water then frequent calibration is unnecessary, as in this case the activity (series capacity) of the platinum layer is not very important and the deposition of highly isolating sub- Figure 13: Cell constants and recommended conductivity intervals. stances is not to be expected. The measuring cell must be thoroughly cleaned after calibration in order to avoid incorrect measuring results caused by adherent KCl solu- tion. Table 15: Recommended cell constants Cell constant Sample –1 c = 0.1 cm For very poorly conducting solutions such as distilled water, deionized or partly deionized water, etc. For applications according to USP 645 and EP 2.2.38 c = 1 cm–1 For moderately conducting solutions such as drinking water, surface water, wastewater, etc. c = 10 cm–1 For solutions with good conductivity such as seawater, rinsing water, physiological solutions, etc. c = 100 cm–1 For solutions with very good conductivity such as electroplating baths, salt solutions, etc.
  • 99. Conductivity measuring cells made ofstainless steel cells should be calibrated before the measurements in order to achieve the highest possible measuring accuracy. 99These are usually substantially more insensitive to con- For cleaning, water and/or ethanol alone should betamination or corrosion. However, also these measuring used.Table 16: Conductivity measurement – interferencesSource of Effects MeasuresinterferenceLow conductivity Values too high, drift Drive off atmospheric CO2 with inert gaswith open vessel (Ar, N2) or use flow-through cell, avoid carryover of salt solutions (e.g. too frequent calibration, inadequate rinsing)Oils, precipitation Isolating layer on electrode g Clean with solvent or oxidizing agentproducts cell constant increases, measuring range limited to higher valuesUnstable Unstable values Temperature compensation, if temperaturetemperature coefficient is known, or thermostatting (temperature coefficient generally approx. 2%/°C)Conductance Stray fields outside electrode shaft Watch distance from vessel duringdepends on (particularly for cells with constants >1 cm-1) calibration and measurement or selectelectrode position g measured value displaced cell constant 1 cm–1 Use of 5-ring conductivity measuring cellsForeign salts Carryover of residual salts when changing Thorough previous rinsing of electrode to solutions with low conductivity g drift to higher valuesAir bubbles Air bubble located between Remove air bubble by tapping electrode plates g unsteady signal2.2. Conductivity measurement in water for bled, a conductivity measuring cell and a conductivity pharmaceutical use according to USP and standard are to be used that allow to determine the cell Pharm. Europe (EP) constant with a maximum measuring error of 2%. ToThere are special requirements for the conductivity meas- prevent the uptake of carbon dioxide, the measurementurement in water for pharmaceutical use («water for should be carried under exclusion of air and/or in a flowinjections») according to USP 645, EP 2.2.38 resp. the cell. The sample fulfills the specification if one of thelatest EP -4.8-07/2004:0169. Besides a precision conduc- following three conditions is met:tometer whose temperature compensation can be disa-
  • 100. 100 Stage 1: The sample is measured directly without further pretreat- Stage 3: However, if the sample does not fulfill the specification ment and without temperature compensation. If the of stage 2, a sample of exactly 100 mL is mixed with 0.3 water fulfills the specification indicated in table 17, the mL saturated KCl solution. Then the pH value of this solu- test is considered as passed. tion is measured exactly to 0.1 pH units. Only if the conductivity fulfills the conditions specified in table 18 Stage 2: the test is considered as passed. Otherwise the water If the conditions are not fulfilled by stage 1, continue as cannot be used for pharmaceutical purposes. follows: The conductivity of at least 100 mL sample is measured under strong agitation at 25 °C ±1 °C as soon as the drift caused by the uptake of carbon dioxide is smaller than 0.1 μS/cm per five minutes. If the measured value is smaller than 2.1 μS/cm, the test is considered as passed. Table 17: First step of the conductivity measurement according to USP 645 and EP -4.8-07/2004:0169 Temperature Conductivity Temperature Conductivity not larger than (μS/cm) not larger than (μS/cm) 0 0.6 55 2.1 5 0.8 60 2.2 10 0.9 65 2.4 15 1.0 70 2.5 20 1.1 75 2.7 25 1.3 80 2.7 30 1.4 85 2.7 35 1.5 90 2.7 40 1.7 95 2.9 45 1.8 100 3.1 50 1.9 Table 18: pH and conductivity criteria for stage 3 pH Conductivity pH Conductivity not larger than (μS/cm) not larger than (μS/cm) 5.0 4.7 6.1 2.4 5.1 4.1 6.2 2.5 5.2 3.6 6.3 2.4 5.3 3.3 6.4 2.3 5.4 3.0 6.5 2.2 5.5 2.8 6.6 2.1 5.6 2.6 6.7 2.6 5.7 2.5 6.8 3.1 5.8 2.4 6.9 3.8 5.9 2.4 7.0 4.6 6.0 2.4
  • 101. 3. Temperature measurementOnly a few of the electrodes offered are fitted with abuilt-in temperature sensor. The decision whether tem- pensation. Under such circumstances it is possible to dispense with the use of a temperature sensor. 101perature measurement/compensation is necessary de-pends on the required accuracy. Differing diffusion However, if a high degree of reproducibility of the meas-potentials, e.g. in highly concentrated or very dilute solu- ured values is demanded or if GLP requirements have totions, or changes to the diaphragm or the membrane be met then temperature measurement/compensation isglass can result in measuring errors that are far in excess absolutely necessary.of the errors caused by the absence of temperature com-Table 19: Temperature measurement or temperature compensation: yes or no?Measurement requirements Temperature compensation or measurementAre GLP requirements to be met? Yes: temperature measurementIs high measuring accuracy required? Yes: temperature compensation (see Nernst potential)Direct measurement? Yes: temperature compensation (see Nernst potential)Titration? No: relative measurementIs the pH of the sample about 7? Yes: temperature compensation not absolutely necessary (low influence, as electrode zero point is at pH = 7), possibly temperature measurementDoes the pH value differ greatly from pH 7? Yes: temperature compensation (see Nernst potential)Are measurements made at different temperatures? Yes: temperature compensation/measurement (see Nernst potential)Is the pH of the sample solution very temperature- Yes: temperature measurement (measurementdependent? temperature must be mentioned)Does the application require a different type of Yes: separate temperature sensor (electrodes withdiaphragm than a ceramic pin? built-in temperature sensors are only available with ceramic pin and fixed ground joint)Is the working life of the electrode very short? Yes: for cost reduction use separate temperature sensor
  • 102. Technical specifications102 6.01 - 6.02 pH glass electrodes Temperature range short-term (°C) Temperature range long-term (°C) Max. installation length (mm) Shaft diameter bottom (mm) Min. immersion depth (mm) Shaft diameter (mm) Temperature sensor Shaft material Plug-in head pH range Shape 6.0150.100 142 12 12 15 Glass G 0...80 0...80 Sphere 0...14 6.0220.100 113 12 12 15 PP G 0...80 0...80 Hemisphere 0...14 6.0221.100 125 12 12 20 Glass G 0...60 0...60 Hemisphere 1...11 6.0221.600 125 12 12 20 Glass U NTC 0...60 0...60 Hemisphere 1...11 6.0224.100 113 12 3 7 Glass G 0...60 0...60 Hemisphere 1...11 6.0226.100 98 12 6 10 Glass G 0...60 0...40 Needle 1...11 6.0228.000 113 12 12 15 PP Fixed cable with plug F Pt1000 (4 mm) 0...80 0...80 Hemisphere 0...14 6.0228.010 113 12 12 15 PP Fixed cable with plug F NTC (2 mm) 0...80 0...80 Hemisphere 0...14 6.0228.020 113 12 12 15 PP Fixed cable with plug I NTC (2 mm) 0...80 0...80 Hemisphere 0...14 (IP67) 6.0229.100 113 12 12 30 Glass G 0...70 0...70 Sphere 0...14 6.0233.100 113 12 12 20 Glass G 0...80 0...80 Hemisphere 0...14 6.0234.100 113 12 6.4 20 Glass G 0...80 0...80 Hemisphere 0...14 6.0234.110 168 12 6.4 20 Glass G 0...80 0...80 Hemisphere 0...14 6.0235.200 125 12 12 20 Glass G 0...80 0...80 Hemisphere 0...14 6.0239.100 113 12 12 30 Glass G 0...80 0...80 Hemisphere 0...14 6.0248.020 288 12 12 25 Glass Fixed cable with plug F Pt1000 (4 mm) 0...100 0...80 Cylinder 0...14 6.0248.030 438 12 12 25 Glass Fixed cable with plug F Pt1000 (4 mm) 0...100 0...80 Cylinder 0...14 6.0253.100 125 12 12 20 Glass G 0...60 0...60 Sphere 0...13 6.0255.100 113 12 12 30 Glass G 0...100 0...70 Cylinder 0...14 6.0255.110 170 12 12 30 Glass G 0...100 0...70 Cylinder 0...14 6.0255.120 310 12 12 30 Glass G 0...100 0...70 Cylinder 0...14 6.0256.100 125 12 12 1 Glass G 0...70 0...60 Flat membrane 0...13 6.0257.000 125 12 12 20 Glass Fixed cable with plug F Pt1000 (4 mm) 0...60 0...60 Sphere 0...13 6.0257.020 260 12 12 20 Glass Fixed cable with plug F Pt1000 (4 mm) 0...60 0...60 Sphere 0...13 6.0258.000 113 12 12 25 Glass Fixed cable with plug F Pt1000 (4 mm) 0...100 0...80 Cylinder 0...14 6.0258.010 113 12 12 25 Glass Fixed cable with plug F Pt1000 (2 mm) 0...100 0...80 Cylinder 0...14 6.0258.600 113 12 12 30 Glass U Pt1000 0...100 0...80 Cylinder 0...14 6.0259.100 113 12 12 25 Glass G 0...100 0...80 Cylinder 0...14 6.0262.100 113 12 12 20 Glass G 0...80 0...80 Hemisphere 0...13 6.0269.100 125 12 12 20 Glass G 0...80 0...80 Sphere 0...13 6.0277.300 125 12 12 20 Glass K Pt1000 0...60 0...60 Sphere 0...13 6.0278.300 113 12 12 30 Glass K Pt1000 0...100 0...80 Cylinder 0...14 6.0279.300 113 12 12 30 Glass K 0...70 0...70 Sphere 0...14 6.0280.300 113 12 12 20 Glass K 0...80 0...80 Hemisphere 0...13
  • 103. 103 Membrane resistance (MΩ) Asymmetry potential (mV) Electrode zero point (mV) Reference resistance (kΩ) Electrolyte outflow (μL/h) Reference electrolyte Reference systemMembrane glass Electrode slope DiaphragmT 40...150 0...±15 > 0.97 0...±15 - c(KCl) = 3 mol/L - - -T 200...400 0...±15 > 0.97 0...±15 Ceramic c(KCl) = 3 mol/L 3...10 LL system 5E < 400 0...±15 > 0.97 0...±15 Twin pore Gel 0 LL system < 20E < 400 0...±15 > 0.97 0...±15 Twin pore Gel 0 LL system < 20M 300...600 0...±15 > 0.97 0...±15 Platinum wire Idrolyte 3...30 LL system 30T 200...500 0...±15 > 0.97 0...±15 Twin pore Gel 0 LL system 20T 200...400 0...±15 > 0.97 0...±15 Ceramic c(KCl) = 3 mol/L 3...10 LL system 5T 200...400 0...±15 > 0.97 0...±15 Ceramic c(KCl) = 3 mol/L 3...10 LL system 5T 200...400 0...±15 > 0.97 0...±15 Ceramic c(KCl) = 3 mol/L 3...10 LL system 5T 40...150 10...60 > 0.90 0...±15 Ground joint LiCl/EtOH 0.4...1.2 LL system < 100T 150...400 0...±15 > 0.97 0...±15 Ceramic c(KCl) = 3 mol/L 10...25 LL system 5T 200...500 0...±15 > 0.97 0...±15 Ceramic c(KCl) = 3 mol/L 5...15 LL system 5T 200...500 0...±15 > 0.97 0...±15 Ceramic c(KCl) = 3 mol/L 5...15 LL system 5T 200...400 0...±15 > 0.97 0...±15 Double capillary Porolyte 5...30 LL system < 15 (ceramic)T 150...400 0...±15 > 0.97 0...±15 Ground joint c(KCl) = 3 mol/L 20...100 LL system 5U 150...500 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 3...30 LL system 5U 150...500 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 3...30 LL system 5A 80...200 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L (gel) 5...20 LL system 50U 150...500 0...±15 > 0.97 0...±15 Ground joint c(KCl) = 3 mol/L 20...100 LL system 5U 150...500 0...±15 > 0.97 0...±15 Ground joint c(KCl) = 3 mol/L 20...100 LL system 5U 150...500 0...±15 > 0.97 0...±15 Ground joint c(KCl) = 3 mol/L 20...100 LL system 5spec. < 2000 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L <2 LL system 5A 80...200 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L (gel) 5...20 LL system 50A 80...200 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L (gel) 5...20 LL system 50U 150...500 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 3...30 LL system 5U 150...500 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 3...30 LL system 5U 150...500 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 3...30 LL system 5U 150...500 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 3...30 LL system 5E 150...400 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 5...30 LL system 5E 80...200 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 5...30 LL system 10A 80...200 0...±15 > 0.97 0...±15 Fixed ground joint Gel 5...20 LL system 50U 150...500 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 3...30 LL system 5T 40...500 10...60 > 0.90 0...±15 Ground joint LiCl/EtOH 0.4...1.2 LL system < 100E < 400 0...±15 > 0.97 0...±15 Fixed ground joint c(KCl) = 3 mol/L 5...30 LL system <5
  • 104. Technical specifications104 Temperature range long-term (°C) 6.03 Separate metal electro- Temperature range short-term Max. installation length (mm) Shaft diameter bottom (mm) Min. immersion depth (mm) Shaft diameter (mm) Measuring range Shaft material Plug-in head pH range Shape Type des (°C) 6.0301.100 125 12 12 10 Glass G Pt -20...70 -20...70 Wire -2000...2000 mV 0...14 6.0309.100 101 12 12 10 Glass G Pt -20...70 -20...70 Sheet -2000...2000 mV 0...14 6.0338.100 96 8 8 5 Glass G Pt -20...70 -20...70 Wire -2000...2000 mV 0...14 6.0340.000 103 5.3 5.3 10 Glass Fixed cable/ Pt -20...70 -20...70 Wire -2000...2000 mV 0...14 Plug F 6.0341.100 101 12 8.75 10 Glass G Pt -20...70 -20...70 Wire -2000...2000 mV 0...14 6.0343.000 86 8 8 10 Plastic Clamp con- Pt 0...80 0...80 Rod -2000...2000 mV 0...14 nection VA 6.0344.100 147 24 24 15 Glass G Pt -20...70 -20...70 Grid/Sheet 0...14 6.0345.100 147 24 24 15 Glass G Pt -20...70 -20...70 Grid/Sheet 0...14 6.0350.100 125 12 12 7 Glass G Ag -20...80 -20...80 Ring -2000...2000 mV 0...14 6.0351.100 125 12 12 7 Glass G Pt -20...80 -20...80 Ring -2000...2000 mV 0...14 6.0352.100 125 12 12 7 Glass G Au -20...80 -20...80 Ring -2000...2000 mV 0...14 Temperature range long-term (°C) 6.04 Combined metal electro- Temperature range short-term Max. installation length (mm) Shaft diameter bottom (mm) Min. immersion depth (mm) Diaphragm resistance (kΩ) Reference resistance (kΩ) Electrolyte outflow (μL/h) Reference electrolyte Shaft diameter (mm) Reference system Measuring range Shaft material Plug-in head Diaphragm pH range Shape Type des (°C) 6.0421.100 113 12 12 10 Noryl/ G Sb rod 0...70 0...70 2...11 Ceramic c(KCl)= 3...10 1.2...1.8 LL system 5 PP 3 mol/L 6.0430.100 125 12 12 20 Glass G Ag/pH 0...80 0...80 Ring/hemi- -2000...2000 0...14 pH 150...400 sphere mV 6.0431.100 125 12 12 20 Glass G Pt/pH 0...80 0...80 Ring/hemi- -2000...2000 0...14 pH 150...400 sphere mV 6.0433.110 178 12 6.4 15 Glass G Ag/pH 0...80 0...80 Ring/hemi- -2000...2000 0...14 pH 200...500 sphere mV 6.0434.110 178 12 6.4 15 Glass G Pt/pH 0...80 0...80 Ring/hemi- -2000...2000 0...14 pH 200...500 sphere mV 6.0435.110 178 12 6.4 15 Glass G Au/pH 0...80 0...80 Ring/hemi- -2000...2000 0...14 pH 200...500 sphere mV 6.0450.100 113 12 12 15 Glass G Ag -5...80 -5...80 Ring -2000...2000 0...14 Ceramic c(KNO3= 10...25 0.4...0.9 LL system 5 mV 1 mol/L 6.0451.100 113 12 12 15 Glass G Pt -5...80 -5...80 Ring -2000...2000 0...14 Ceramic c(KCl)= 10...25 0.4...0.9 LL system 5 mV 3 mol/L 6.0452.100 113 12 12 15 Glass G Au -5...80 -5...80 Ring -2000...2000 0...14 Ceramic c(KCl)= 10...25 0.4...0.9 LL system 5 mV 3 mol/L 6.0470.300 125 12 12 20 Glass K Ag/pH 0...80 0...80 Ring/hemi- -2000...2000 0...14 pH 150...400 sphere mV 6.0471.300 125 12 12 20 Glass K Pt/pH 0...80 0...80 Ring/hemi- -2000...2000 0...14 pH 200...500 sphere mV
  • 105. 105 Temperature range long-term (°C) Temperature range short-term Max. installation length (mm) Shaft diameter bottom (mm) Min. immersion depth (mm) Shaft diameter (mm)6.05 Ion-selective Measuring range Shaft material Plug-in headelectrodes pH range Shape Type (°C) 6.0501.100 86 12 12 20 Glass G Glass (Na) 0...80 0...80 Sphere 1x10-5...1 mol/L 5...9 -6 6.0502.100 123 12 12 1 EP G Crystal (Br) 0...50 0...50 Flat 5x10 ...1 mol/L 0...14 -7 6.0502.110 123 12 12 1 EP G Crystal (Cd) 0...80 0...80 Flat 1x10 ...0.1 mol/L 2...12 -6 6.0502.120 123 12 12 1 EP G Crystal (Cl) 0...50 0...50 Flat 5x10 ...1 mol/L 0...14 -6 -2 6.0502.130 123 12 12 1 EP G Crystal (CN) 0...80 0...80 Flat 8x10 ...10 mol/L 10...14 -8 6.0502.140 123 12 12 1 EP G Crystal (Cu) 0...80 0...80 Flat 1x10 ...0.1 mol/L 2...12 -6 6.0502.150 123 12 12 1 EP G Crystal (F) 0...80 0...80 Flat 1x10 ...sat. mol/L 5...7 -8 6.0502.160 123 12 12 1 EP G Crystal (I) 0...50 0...50 Flat 5x10 ...1 mol/L 0...14 -6 6.0502.170 123 12 12 1 EP G Crystal (Pb) 0...80 0...80 Flat 1x10 ...0.1 mol/L 4...7 -7 6.0502.180 123 12 12 1 EP G Crystal (Ag/S) 0...80 0...80 Flat 1x10 ...1 mol/L 2...12 -6 6.0502.190 123 12 12 1 EP G Crystal (SCN) 0...50 0...50 Flat 5x10 ...1 mol/L 2...10 -7 6.0504.100 123 12 12 1 EP/PVC G Polymer (Ca) 0...40 0...40 Flat 5x10 ...1 mol/L 2.5...11 -6 6.0504.110 123 12 12 1 EP/PVC G Polymer (K) 0...40 0...40 Flat 1x10 ...1 mol/L 2.5...11 -6 6.0504.120 123 12 12 1 EP/PVC G Polymer (NO3) 0...40 0...40 Flat 7x10 ...1 mol/L 2.5...11 -6 6.0506.100 123 12 12 5 PEEK/POM G NH3-permeable 0...40 0...40 Flat 5x10 ...1 mol/L 11 membrane 6.0507.010 123 12 2.5 20 PPO G Non-ionic surfactants 0...40 0...40 Pin surfactant- 0...12 dependent 6.0507.120 123 12 2.5 20 PPO G Non-ionic surfactants 0...40 0...40 Pin surfactant- 0...12 dependent 6.0507.130 108 12 12 1 POM G Ionic surfactants 10...50 10...50 Flat surfactant- 0...10 dependent 6.0507.140 123 12 12 1 PEEK G Ionic surfactants 0...40 0...40 Flat surfactant- 0...13 dependent 6.0507.150 123 12 2.5 20 PPO G Ionic surfactants 0...40 0...40 Pin surfactant- 0...12 dependent -7 6.0508.100 123 12 12 1 PVC G Polymer (Na) 0...40 0...40 Flat 5x10 ...1 mol/L 3...12 -7 6.0508.110 123 12 12 1 PVC G Polymer (Ca) 0...40 0...40 Flat 5x10 ...1 mol/L 2...12
  • 106. Technical specifications106 Temperature range long-term (°C) Temperature range short-term (°C) 6.07 Reference electrodes Max. installation length (mm) Shaft diameter bottom (mm) Min. immersion depth (mm) Diaphragm resistance (kΩ) Reference resistance (kΩ) Reference electrolyte Shaft diameter (mm) Reference system Shaft material Plug-in head Diaphragm pH range 6.0724.140 43 12 8 20 Glass B 0...80 0...80 6.0726.100 97 12 12 10 Glass B 0...80 0...80 Ground joint variable variable variable Ag wire/AgCl variable 6.0726.107 97 12 12 10 Glass B 0...80 0...80 Ground joint c(KCl) = 3 mol/L 5...30 <1 Ag wire/AgCl < 1 6.0726.108 97 12 12 10 Glass B 0...80 0...80 Ground joint LiCl(sat) in ethanol 0.1...0.8 < 200 Ag wire/AgCl < 200 6.0726.110 108 12 8 10 Glass B 0...80 0...80 Ground joint variable variable variable Ag wire/AgCl variable 6.0727.000 83 18 18 PTCFE Plug pin Ceramic c(KCl) = 3 mol/L 0.4...0.9 2 mm 6.0728.000 65 12 7 10 PTCFE Clamping screw 0...60 0...60 Ceramic variable Ag wire/AgCl 6.0728.010 78 15 12 10 PTCFE Clamping screw 0...60 0...60 Ceramic variable Ag wire/AgCl 6.0728.020 78 15 12 10 PTCFE Clamping screw 0...60 0...60 Ceramic c(KCl) = 3 mol/L Ag wire/AgCl 6.0728.030 78 15 12 10 PTCFE Clamping screw 0...60 0...60 Ceramic c(KCl) = 3 mol/L LL system 6.0729.100 97 12 12 10 Glass G 0...80 0...80 Ground joint variable variable variable Ag wire/AgCl variable 6.0729.108 97 12 12 10 Glass G 0...80 0...80 Ground joint LiCl(sat) in ethanol 0.1...0.8 < 200 Ag wire/AgCl < 200 6.0729.110 140 12 12 10 Glass G 0...80 0...80 Ground joint variable variable variable Ag wire/AgCl variable 6.0733.100 125 12 12 10 Glass B 0...80 0...80 Ceramic c(KCl) = 3 mol/L 5...15 0.4...0.9 LL system 3 6.0736.110 178 12 6.4 10 Glass B 0...80 0...80 Ground joint variable variable variable Ag wire/AgCl variable 6.0750.100 125 12 12 1 Glass B 0...80 0...80 Fixed ground variable 5...30 variable Ag wire/AgCl variable joint Temperature range long-term (°C) 6.08-6.11 carbon electrodes, Temperature range short-term Shaft diameter bottom (mm) Min. immersion depth (mm) Installation length (mm) temperature sensors Shaft diameter (mm) Conductivity cells, Temperature sensor Measuring range Shaft material Plug-in head Type (°C) 6.0901.040 108 12 20 50 Glass Fixed cable 2xB (4 mm) Pt platinized 5...70 5...70 0.1...10000 μS/cm 6.0901.260 125 12 20 80 Glass Fixed cable 2xB (4 mm) Pt platinized 5...70 5...70 10...1000000 μS/cm 6.0908.110 123 12 12 40 Glass Fixed cable 4xB (4 mm) Pt platinized 5...70 5...70 1...100000 μS/cm Pt100 6.0910.120 120 12 12 16 Glass G Pt platinized 5...70 5...70 1...100000 μS/cm 6.0912.110 125 12 12 30 PP Fixed cable 4xB (4 mm) Pt platinized 5...70 5...70 1...100000 μS/cm Pt1000 6.0914.040 125 12 12 35 Steel, stainless Fixed cable 4xB (4 mm) Steel, stainless -20...150 -20...150 0...300 μS/cm Pt1000 6.0915.100 125 12 12 34 PEEK Fixed cable, plug N 5-ring, Pt 0...70 0...70 5...20000 μS/cm Pt1000 (ideal) 6.0915.130 142 12 12 50 PEEK Fixed cable, plug N 5-ring, Pt 0...70 0...70 5...100000 μS/cm Pt1000 (ideal) 6.0916.100 133 12 12 35 Steel, stainless Fixed cable, plug N Steel, stainless -20...150 -20...150 0...300 μS/cm Pt1000 6.1103.000 121 12 5 20 Glass Fixed cable 2xB (4 mm) -50...100 -50...100 -50...100 °C Pt100 6.1110.100 125 12 5 20 Glass G -50...180 -50...180 -50...180 °C Pt1000 6.1110.110 178 12 6.4 20 Glass G -50...180 -50...180 -50...180 °C Pt1000 6.1114.010 140 12 3 10 PEEK Fixed cable, plug 2x2 B Stainless steel -50...100 -50...100 -50...100 Pt1000
  • 107. 107
  • 108. Subject to change without notice.Design Ecknauer+Schoch ASW, Printing Metrohm AG, CH-9101 Herisau8.000.5037EN – 2010-7 www.metrohm.com