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Reducing Interferences in Cyanide Analysis William Lipps Market Specialist – Water Analyzer Products OI Analytical
This talk presents problems and solutions in cyanide analysis 1. What we measure 2. Problems HCN CN - 3. Solutions
Cyanide methods measure the various cyanide “species” Total CN Strong   Metal Complexes Fe, Co, Pt, Au Available CN Weak t...
If all we had was CN -  in dilute NaOH it would be easy
Direct colorimetry does not correlate with distillation results
Direct ISE does not correlate with distilled real sample results
Cyanide methods require separation of CN from matrix <ul><li>Separated from interferences, cyanide measurement is no diffe...
Distillation most common technique to remove interference Macro Distillation MIDI Distillations
Distillation actually creates CN interferences <ul><li>Boiling acid </li></ul><ul><li>Automated UV-Distillation </li></ul>...
Interferences with distillation are in almost every sample <ul><li>Thiocyanate </li></ul><ul><li>Sulfur </li></ul><ul><li>...
Thiocyanate + Nitrate results in positive bias <ul><li>The addition of Sulfamic acid does not sufficiently reduce this int...
Sulfur compounds react rapidly with CN <ul><li>Elemental Sulfur </li></ul><ul><ul><li>8CN -  + S 8    SCN - </li></ul></u...
Thiosulfate reacts with cyanide during distillation <ul><li>0.200 mg/L CN -  + 200 mg/L S 2 O 3 -2 </li></ul><ul><ul><li>C...
Sulfite reacts rapidly with CN in basic solutions <ul><li>0.200 mg/L CN -  + 200 mg/L SO 3 -2 </li></ul><ul><ul><li>Cyanid...
There is no way to “know” if sulfur compounds are present <ul><li>No “spot” tests that adequately detect the sulfur compou...
Oxidizers destroy cyanide before or during distillation <ul><li>Hypochlorite </li></ul><ul><li>Peroxide </li></ul><ul><li>...
Footnote 6 (MUR 2007) allows other methods to be used <ul><li>More accurate? </li></ul><ul><ul><li>Spikes? </li></ul></ul>...
Matrix spikes cannot be used to demonstrate accuracy Both methods detected CN -  in a synthetic sample  with no CN - . 98 ...
Verify Accuracy Using Interference Free Methods <ul><li>Use methods demonstrated by literature and multiple users to be in...
The old versus the new HCN CN - Purging and boiling in acid Diffusion at room temperature
Electrochemistry techniques integrate matrix removal   <ul><li>Very sensitive with large dynamic range. </li></ul>
Unlike colorimetry, GD amperometry is easy to visualize <ul><li>CN -  + H +     HCN </li></ul><ul><li>HCN + OH -     CN ...
This flow diagram illustrates the simplicity of GD-amperometry Acid
A series of GD-amperometry CN methods to meet needs <ul><li>Free cyanide </li></ul><ul><li>Available cyanide </li></ul><ul...
The only fully automated free cyanide method Measurement Description Method Gas Diffusion-Amperometry FIA ASTM D 7237
Direct colorimetry is not measuring free cyanide
The free cyanide method by GD-amperometry ASTM D7237-06 Buffer
Real Data Comparison – Free CN
GD-amperometry methods for available cyanide – no CATC! No distillation or pyridine required Gas Diffusion - Amperometry L...
Sulfide does not interfere
Quantitative recovery compared to other methods such as CATC OIA1677 OIA 1677
Precise and more accurate than WAD methods OIA1677
GD-amperometry available CN has fewer interferences Concentration Dependent S 2 O 3 , H 2 O 2 Concentration Dependent SCN,...
GD-amperometry available CN saves time and labor 1 – 2 minutes 3 – 4 hours 3 – 4 hours Total Time 1 – 2 minutes 1 – 2 minu...
Less manipulation means better Available CN data <ul><li>No distillation  </li></ul><ul><li>0.5 ppb MDL </li></ul><ul><li>...
Easy to use, understand, and environmentally friendly OIA 1677, ASTM D6888-04 or ASTM D7284-08 No pyridine Acid Reagent
Total cyanide methods using manual distillation Automated Colorimetry Midi Distillation – MgCl 2 EPA 335.4 Gas Diffusion -...
Most total cyanide analyses are by EPA 335.4 or similar <ul><li>Manual distillation </li></ul><ul><li>Prolonged heating (1...
ASTM D7284 manual distillation GD-amperometry method <ul><li>Distill samples </li></ul><ul><li>Use GD-amperometry </li></u...
Colorimetry and GD- amperometry compare favorably
Once again, sulfide does not interfere with GD-amperometry
But wait, I thought distillation was bad?
Comparison of Measurements with Interferences Present 49 47 200 ppb + Ascorbate + Ammonia + OCL - 71 73 200 ppb + Ascorbat...
What exactly do “total” cyanide methods measure? <ul><li>Iron Cyanide + Available CN   </li></ul>
Iron cyanide is not toxic. <ul><li>Sunlight causes iron cyanide to release HCN </li></ul><ul><li>Sunlight = UV irradiation...
Automated total cyanide methods use UV to liberate HCN from Fe Gas Diffusion - Amperometry Low power  UV -  pH <2 OIA 1678...
Comparison of Kelada and ASTM D7511-09 0.01 – 0.03 % 0.25 – 0.5 % SCN Interaction No Yes Distillation No Pyridine Pyridine...
For total cyanide, simply add UV irradiation to the GD method No pyridine OIA1678 / ASTM D7511-09
Same results with and without flash distillation Distillation is not necessary
Same, but more precise results as manual distillation OIA 1678 UV GD-Amperometry EPA 335.4 Semi-automated Colorimetry
ASTM D7511 and D7284 get the same result if no interferences
Comparison of Total CN methods 1 – 2 minutes 2 – 4 hours 3 – 4 hours Total Time 1 – 2 minutes 1 – 2 minutes 1 – 2 minutes ...
Benefits Distillation / Colorimetry GD-Amperometry In summary, distillation/colorimetry should be replaced
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The Analytical Methods And Technologies Of Cyanide Chemistry Training

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The Analytical Methods And Technologies Of Cyanide Chemistry Training

  1. 1. Reducing Interferences in Cyanide Analysis William Lipps Market Specialist – Water Analyzer Products OI Analytical
  2. 2. This talk presents problems and solutions in cyanide analysis 1. What we measure 2. Problems HCN CN - 3. Solutions
  3. 3. Cyanide methods measure the various cyanide “species” Total CN Strong Metal Complexes Fe, Co, Pt, Au Available CN Weak to Moderately Strong Metal Complexes Ag, Cd, Cu, Hg, Ni, Zn Free CN HCN CN -
  4. 4. If all we had was CN - in dilute NaOH it would be easy
  5. 5. Direct colorimetry does not correlate with distillation results
  6. 6. Direct ISE does not correlate with distilled real sample results
  7. 7. Cyanide methods require separation of CN from matrix <ul><li>Separated from interferences, cyanide measurement is no different than running standards. </li></ul>
  8. 8. Distillation most common technique to remove interference Macro Distillation MIDI Distillations
  9. 9. Distillation actually creates CN interferences <ul><li>Boiling acid </li></ul><ul><li>Automated UV-Distillation </li></ul><ul><ul><li>Boiling acid </li></ul></ul>
  10. 10. Interferences with distillation are in almost every sample <ul><li>Thiocyanate </li></ul><ul><li>Sulfur </li></ul><ul><li>Thiosulfate/Sulfite </li></ul><ul><li>Oxidizers </li></ul>
  11. 11. Thiocyanate + Nitrate results in positive bias <ul><li>The addition of Sulfamic acid does not sufficiently reduce this interference . </li></ul><ul><ul><li>A real POTW sample with 0.1 mg/L SCN - and 63.5 mg/L NO 3 - detected total CN - at 0.10 mg/L even after the addition of Sulfamic Acid </li></ul></ul>
  12. 12. Sulfur compounds react rapidly with CN <ul><li>Elemental Sulfur </li></ul><ul><ul><li>8CN - + S 8  SCN - </li></ul></ul><ul><li>Metal Sulfides </li></ul><ul><ul><li>Cu 2 S, FeS, PbS, CuFeS 2 , CdS, ZnS, etc. </li></ul></ul><ul><ul><li>S reacts with CN - to form SCN - </li></ul></ul>
  13. 13. Thiosulfate reacts with cyanide during distillation <ul><li>0.200 mg/L CN - + 200 mg/L S 2 O 3 -2 </li></ul><ul><ul><li>Cyanide Found = 0.160 mg/L </li></ul></ul><ul><ul><li>Recovery = 80%* </li></ul></ul><ul><ul><li>* Double Chloramine T added, or recovery would be lower. </li></ul></ul>
  14. 14. Sulfite reacts rapidly with CN in basic solutions <ul><li>0.200 mg/L CN - + 200 mg/L SO 3 -2 </li></ul><ul><ul><li>Cyanide Found = 0.000 mg/L </li></ul></ul><ul><ul><li>Recovery = 0% </li></ul></ul><ul><li>This reaction occurs in absorber solution, or in preserved sample </li></ul>
  15. 15. There is no way to “know” if sulfur compounds are present <ul><li>No “spot” tests that adequately detect the sulfur compounds </li></ul><ul><li>Sodium sulfite and sodium thiosulfate are both added to samples for dechlorination. </li></ul>
  16. 16. Oxidizers destroy cyanide before or during distillation <ul><li>Hypochlorite </li></ul><ul><li>Peroxide </li></ul><ul><li>Caro’s Acid </li></ul><ul><li>Chloramines </li></ul>
  17. 17. Footnote 6 (MUR 2007) allows other methods to be used <ul><li>More accurate? </li></ul><ul><ul><li>Spikes? </li></ul></ul><ul><li>“ challenge matrix” distilled </li></ul>
  18. 18. Matrix spikes cannot be used to demonstrate accuracy Both methods detected CN - in a synthetic sample with no CN - . 98 % 16 335.3 98 % 32 335.4 Recovery Amount Detected (ppb) Method
  19. 19. Verify Accuracy Using Interference Free Methods <ul><li>Use methods demonstrated by literature and multiple users to be interference free </li></ul><ul><ul><li>OIA 1677 or ASTM D6888-04 </li></ul></ul><ul><ul><li>ASTM D 7284-08 </li></ul></ul><ul><ul><li>OIA 1678 (ASTM D7511-09) </li></ul></ul>
  20. 20. The old versus the new HCN CN - Purging and boiling in acid Diffusion at room temperature
  21. 21. Electrochemistry techniques integrate matrix removal <ul><li>Very sensitive with large dynamic range. </li></ul>
  22. 22. Unlike colorimetry, GD amperometry is easy to visualize <ul><li>CN - + H +  HCN </li></ul><ul><li>HCN + OH -  CN - + H2O </li></ul><ul><li>Ag + 2CN -  Ag(CN) 2 - + e - </li></ul>measure
  23. 23. This flow diagram illustrates the simplicity of GD-amperometry Acid
  24. 24. A series of GD-amperometry CN methods to meet needs <ul><li>Free cyanide </li></ul><ul><li>Available cyanide </li></ul><ul><li>Total distilled cyanide </li></ul><ul><li>Total non-distilled cyanide </li></ul>
  25. 25. The only fully automated free cyanide method Measurement Description Method Gas Diffusion-Amperometry FIA ASTM D 7237
  26. 26. Direct colorimetry is not measuring free cyanide
  27. 27. The free cyanide method by GD-amperometry ASTM D7237-06 Buffer
  28. 28. Real Data Comparison – Free CN
  29. 29. GD-amperometry methods for available cyanide – no CATC! No distillation or pyridine required Gas Diffusion - Amperometry Ligand Exchange / Flow Injection Analysis ASTM D 6888 Measurement Description Method Number Descriptive Name Gas Diffusion - Amperometry Ligand Exchange / Flow Injection Analysis OIA 1677 Available Cyanide
  30. 30. Sulfide does not interfere
  31. 31. Quantitative recovery compared to other methods such as CATC OIA1677 OIA 1677
  32. 32. Precise and more accurate than WAD methods OIA1677
  33. 33. GD-amperometry available CN has fewer interferences Concentration Dependent S 2 O 3 , H 2 O 2 Concentration Dependent SCN,NH 3 ,NO 2 None Excessive Iron Cyanide N-organics OIA 1677 WAD CATC
  34. 34. GD-amperometry available CN saves time and labor 1 – 2 minutes 3 – 4 hours 3 – 4 hours Total Time 1 – 2 minutes 1 – 2 minutes 1 – 2 minutes Analysis No distillation 1 distillation 2 – 3 hours 2 distillations 2 – 3 hours Sample Preparation OIA 1677 WAD CATC
  35. 35. Less manipulation means better Available CN data <ul><li>No distillation </li></ul><ul><li>0.5 ppb MDL </li></ul><ul><li>Up to 90 samples per hour </li></ul><ul><li>Ease of Operation </li></ul><ul><li>Very simple chemistry </li></ul>
  36. 36. Easy to use, understand, and environmentally friendly OIA 1677, ASTM D6888-04 or ASTM D7284-08 No pyridine Acid Reagent
  37. 37. Total cyanide methods using manual distillation Automated Colorimetry Midi Distillation – MgCl 2 EPA 335.4 Gas Diffusion - Amperometry Midi / Micro Distillation – MgCl 2 ASTM D 7284 Total Cyanide Measurement Description Method Number Descriptive Name
  38. 38. Most total cyanide analyses are by EPA 335.4 or similar <ul><li>Manual distillation </li></ul><ul><li>Prolonged heating (125 °C) , strong acid (pH <2) </li></ul><ul><li>Purging into basic absorber solution </li></ul><ul><li>Colorimetry </li></ul>
  39. 39. ASTM D7284 manual distillation GD-amperometry method <ul><li>Distill samples </li></ul><ul><li>Use GD-amperometry </li></ul><ul><li>No pyridine </li></ul><ul><li>Fewer interferences </li></ul>
  40. 40. Colorimetry and GD- amperometry compare favorably
  41. 41. Once again, sulfide does not interfere with GD-amperometry
  42. 42. But wait, I thought distillation was bad?
  43. 43. Comparison of Measurements with Interferences Present 49 47 200 ppb + Ascorbate + Ammonia + OCL - 71 73 200 ppb + Ascorbate + Ammonia 154 152 200 ppb + Ascorbate 159 147 200 ppb + SO 3 229 227 20 ppb +SCN + NO 3 18.4 18.7 20 ppb ASTM D7284 EPA 335.4 Sample (Total CN)
  44. 44. What exactly do “total” cyanide methods measure? <ul><li>Iron Cyanide + Available CN </li></ul>
  45. 45. Iron cyanide is not toxic. <ul><li>Sunlight causes iron cyanide to release HCN </li></ul><ul><li>Sunlight = UV irradiation </li></ul>[Fe(CN) 6 ] -3 + H + _ 6 HCN + Fe +3 hv
  46. 46. Automated total cyanide methods use UV to liberate HCN from Fe Gas Diffusion - Amperometry Low power UV - pH <2 OIA 1678/ASTM D7511 Automated Colorimetry Low power UV - Auto distillation pH <2 EPA 335.3 Automated colorimetry High power UV- Auto distillation Alkaline pH ASTM D4374 (Kelada 01) Total Cyanide Measurement Description Method Number Descriptive Name
  47. 47. Comparison of Kelada and ASTM D7511-09 0.01 – 0.03 % 0.25 – 0.5 % SCN Interaction No Yes Distillation No Pyridine Pyridine Reagents 5 15 Pump Tubes ASTM D7511 Kelada 01
  48. 48. For total cyanide, simply add UV irradiation to the GD method No pyridine OIA1678 / ASTM D7511-09
  49. 49. Same results with and without flash distillation Distillation is not necessary
  50. 50. Same, but more precise results as manual distillation OIA 1678 UV GD-Amperometry EPA 335.4 Semi-automated Colorimetry
  51. 51. ASTM D7511 and D7284 get the same result if no interferences
  52. 52. Comparison of Total CN methods 1 – 2 minutes 2 – 4 hours 3 – 4 hours Total Time 1 – 2 minutes 1 – 2 minutes 1 – 2 minutes Analysis No distillation 1 – 3 hour distillation 2 – 3 hour distillation Sample Preparation ASTM D7511 ASTM D7284 335.4
  53. 53. Benefits Distillation / Colorimetry GD-Amperometry In summary, distillation/colorimetry should be replaced

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