Understanding Cyanide
Monday, 11 June 2012 07:09

Introduction - Cyanide and its toxic effects on life are fairly well known. Everyone knows the stereotype of the hidden cyanide pill that secret agents carry as a last resort. But cyanide isn’t just for spy thrillers anymore. There are a variety of industries that use cyanide, most notably mining or metal processes. Don’t try to rely on another stereotype of cyanide, the burnt almond odor, to warn you of danger. First off, you might miss out on enjoying some actual almonds and secondly, only those with a specific genetic trait are able to detect cyanide in this manner.

The simple cyanide salts are most toxic in the environment due to their complete dissociation. Most of the transition metals form cyanide complexes having varying degrees of solubility, with iron cyanide complexes being the most stable. The iron-cyanide stability is what leads to its acute toxicity. The cyanide ions bind with certain iron containing proteins and inhibit the energy production in a cell. The nervous system and the heart are most susceptible to this type of disruption. Alkaline chlorination has historically been the most accepted means of treating cyanide in water streams.

Method Summary – The distillation is accomplished using high heat and a strong acid to convert all forms of CN- into HCN gas. This gas is then bubbled through a NaOH scrubbing solution to convert back to CN-. The scrubbing solution now contains all the cyanide that was present in the original sample aliquot and can be analyzed. The titration relies on the reaction of silver nitrate and cyanide with a rhodanine indicator. The ISE analysis utilizes a standard cyanide ISE to detect cyanide ions in solution. The colorimetric methods rely on the conversion of CN- to CNCl and on the subsequent reaction with a pyridine-barbituric acid reagent.

What You Should Know – This particular analysis is one of the most interference prone tests you will find in the inorganic side of environmental analysis. There are several standard interferences that you must check for and address prior to beginning the distillation.

  • Oxidizing agents will decompose most cyanide compounds and are a negative interferant.
  • Sulfides will convert cyanide to thiocyanate at the pH required for preservation. Additionally, the sulfide can oxidize under the test conditions forming sulfite which will consume the chloramine-T in the colorimetric procedure. Sulfide will distill over with the cyanide and continue to present problems.

Click here for a more detailed Lab Matters PDF on Understanding Cyanide


avatar Matt Hadley
Great information. Thank you for your insights.
Name *
ChronoComments by Joomla Professional Solutions
Submit Comment
Show/Hide Comment form