Gas chromatography


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Gas chromatography

  1. 1. GasChromatographyPrepared byAmit Shrestha1st M.pharm(pharmacology)Mallige college of pharmac05-06-2013
  2. 2. HistoryIntroductionPrincipleTheoryInstrumentationCarrier gasFlow regulator Flow meter Injection device Columns Temperature control deviceDetectorApplication
  3. 3. Mikhail Tswett inventedchromatography in 1901during his research onplant pigments.He used the technique toseparate various plantpigments such aschlorophylls, xanthophyllsand carotenoids.Invention of ChromatographyMikhail TswettRussian Botanist(1872-1919)
  4. 4. IntroductionIt is an analytical technique used for separationOf thermal stable and volatile substances.Mobile phase GasStationary phase  Solid (or) LiquidIQualitative technique:Can be used to identify compounds ifstandards are usedQuantitative technique:Can be used to determine relativeamounts of compounds present in amixture
  5. 5. PrinciplesAdsorption (or)partitionDepending on theStationary phase usedIf Stationary phase isliquid Gas Liquid Chromatography PartitionSolid  GAS Solid Chromatography  AdsorptionPrincipleinvolved•In general, compounds with lowboiling points (and high vaporpressures) spend more time in themobile phase and elute from thecolumn in a shorter amount of timethan compounds with high boilingpoints
  6. 6. TheoryThe component to be separatedfrom Gas ChromatographyShould be Volatile & Thermostability
  7. 7. InstrumentationCarrier gasFlow regulator Flow meter Injection device Columns Temperature controldeviceDetector
  8. 8. Schematic of a Commercial Gas Chromatograph
  9. 9. HP 5890 Capillary Gas Chromatographwith Robotic Sample Injector and Data Station
  10. 10. carrier gasthe mobile phase (or “ moving phase")is a carrier gas, usually an inert gassuch as helium or an unreactive gassuch as nitrogenNOTE: Probably more than 90% of the presentGC instruments run with helium as carrier gas.Some people use hydrogen or nitrogenH  Adv: better thermal conductivity , low densitydisadv: it reacts with unsaturated compound& it is inflammable.He  adv: excellent thermal conductivitydisadv: expensiveN adv: inexpensivedisadv: reduced sensitivity
  11. 11. Flow RegulatorAs carrier gases are stored under highPressure, Flow regulator are used to deliver theGas with uniform pressure or flow rateFlow meterRotameterit is placed conveniently before the column inlet. It has an ordinaryglass tube (like burette) with a float held on to spring, the level ofthe float is determined by the flow rate of carrier gas and is precalibrated
  12. 12. Columnmade of glass or metal such as stainless steelstainless steel  long life.handled easily but react with some compoundGlass widely used as they are inert but highly fragileColumn can be used both for preparative and analytic purposeTypesPacked column:GSC:-packed with graded adsorbent or porous polymersGLC:- “ “ liquid phase coated graded inert solid supportOpen tubular column:also called capillary or Golay columnmade up stainless steel with long capillary tubing in length and haveuniform and narrow internal diameterSupport coated open tubular columnimprove version of OTC
  13. 13. Stationary phase:GSC non volatile liquidEx: PEG, Amides., Hydrocarbons, Carbowax etcGLC  interactive solids such as molecular sieves or porous polymersEx: Na & Ca analogue of potassium aluminosilicate,polymer made of acrylic esters
  14. 14. Sample injection system:Injected by Hypodermic Syringe from rubberseptumA hypodermic needle is used for rapiddelivery of liquids
  15. 15. DETECTORS:Flame ionization detectoramplifierHydrogenAir or o2Collector ElectrodePolarising electrodeOperating principleThe operation of the FID is based on the detection of ions formedduring combustion of organic compounds in a hydrogen flame.The generation of these ions is proportional to the concentration oforganic species in the sample gas stream.flameCarrier gas from columnOperation:• At normal temperature and pressure gases acts asinsulator but become conductive if ions are present.• it is also based upon electrical conductivity of carriergases.• when pure gas is passes alone there is no ionization andno current flow.• when component is emerge from column no. of ions areproduced becoz of ionization by the thermal energy ofthe flame. This cause potential difference & cause aflow of current which is amplified & recordedPlatinum capillary at the tip  cathodeSilver gauge above  anodeFID stable and sensitive to small change in flow rate
  16. 16. Advantagesrelatively inexpensive to acquire and operateLow maintenance requirementFIDs are relatively resistant to misuse.Linearity and detection ranges: FIDs can measure organicsubstance concentration at very low and very high levelsDisadvantagescannot differentiate between different organic substancesThey also cannot detect inorganic substances
  17. 17. Thermal conductivity detectoralso known as a Katharometer, is a bulk property detector and a chemicalspecific detector commonly used in gas chromatographyThis detector senses changes in the thermalconductivity of the column effluent and compares it toa reference flow of carrier gas
  18. 18. •Principle  thermal conductivity difference between carrier gasand that of component.•It consists two platinum wires of uniform dimension which formpart of wheat stone bridge.1st wire  carrier gas flow2nd wire  effluents of the column passes•2 platinum wire is heated electrically for equilibrium conditionof temperature and electrical resistance•When sample passes through column it alerts thermalconductivity & resistance of the wire & the difference inthermal conductivity is amplified and recorded as a signal.TCD SchematicTCD SchematicH & He higher thermal conductivity
  19. 19. Advantagesthe device is inexpensive and has good accuracyThe TCD is often called a universal detector because itresponds to all compoundsthe TCD is less sensitive than theflame ionization detector
  20. 20. Overview When each component reaches the detector(OCCC’s instrument uses a TCD), thefilament in the detector heats up, ultimatelyresulting in an electrical signal that isdigitized and sent to the attached computer. A chromatogram is generated.◦ A graph of the intensity ofthe detector’s response asa function of time
  21. 21. Determining Identity The number of components present ina mixture is indicated by the number ofpeaks observed. Under a very specific set of conditions,the retention time for a compound canbe used to help identify a compound.◦ The amount of time from injectionfor a sample to reach the detectorRetention time:it is the difference in time between thepoint of injection & appearance of peak maxima•Retention time varies with changes inthe identity of a compound and withexperimental conditions including:•type and amount of stationary•Phase•length of column,•gas flow rate,•temperature profile
  22. 22. ApplicationLet us check it out some of the applications of gas chromatography. It has many uses as well as applications andadvantages which are useful for the separation of a given unknown mixture. It is a physical method to separate thismixture. Gas Chromatography have many advantages compared to other separation analysis methods.Some of the different applications of gas chromatography where it can be used such as:Used in pharmaceuticalsused in pollutantspetroleumpetrochemicalsoilsfatsfood and flavorsvitaminssteroids and alkaloidsblood and serumpesticides and fungicidesradioactive isotopesused in cosmeticsused in environmental toxins.These are some of the fields where GC can be used for the separation of volatile mixtures.It can also be used for the volatile samples such as human breathe, blood, saliva and other secretions whichcontains organic volatiles and can be easily analyzed with Gas Chromatography.This GC is very much useful in studying of health of human as well as environment. Again gas chromatographyhave many advantages.Air samples can also be analyzed with GC.Air quality control units also use Gas Chromatography in order to determine the components of a given air sample.Manufacturers of Cosmetics also use gas chromatography to effectively measure how much of each chemical isused for their products.
  23. 23. •In general, substances that vaporizebelow ca. 300 °C (and therefore arestable up to that temperature) can bemeasured quantitatively•Very minute amounts of a substancecan be measured