The extensive use of cyanide in everyday industrial operations requires close monitoring with reliable methodologies and instrumentation.
Mention cyanide and you almost always get an over-reaction due to its highly poisonous nature. And rightly so, the cyanide complex (CN-) binds with the enzyme cytochrome C oxidase to inhibit cellular respiration and energy production, resulting in cytotoxic hypoxia that very rapidly affects the central nervous system and heart. In simpler terms, it’s an effective poison for most living organisms.
Yet, it’s also a very useful compound in today’s economies. More than 1 billion kg of cyanide compounds are produced annually in the U.S. alone for a variety of industrial and manufacturing process applications. These include its use in pesticides and fumigants, plastics, electroplating, dyes, textiles, specialty chemicals and pharmaceuticals, petroleum refining, steel production, microelectronics manufacturing, and (mostly) mining. Cyanide is a primary material used in gold mining operations, to leach the gold metal out of low-gold content ores. In mining, as well as in other process situations, there is a significant potential for having the cyanide compounds as process wastes get into the local water supplies. And, of course, the added possibility of the intentional contamination of drinking water and food products with cyanide is a potential Homeland Security threat.
Testing for cyanide
The chemical composition of cyanide in environmental samples is affected by pH, temperature, trace metal content, and the presence of sulfur or sulfur compounds. A number of cyanide species of varying stability may be present in just one sample. For these reasons, cyanide testing can be a challenging analytical task.
As a result, the U.S. Environmental Protection Agency (EPA) has no less than 25 certified laboratory procedures (combined USEPA and ASTM, American Society for Testing and Materials) for analyzing cyanide. The extensive use of cyanide compounds in gold mining operations has also resulted in creation of the International Cyanide Management Institute, Washington, D.C., which has a certification program for the operations of its more than 30 international voluntary signatory companies.
Instrumentation companies as well have created specific systems for monitoring and evaluating the level of cyanide in water supplies and the environment. OI Analytical, College Station, Texas, has a compact modular system, the CNSolution Cyanide Analyzer, for flow injection analysis of available or total cyanide. Available cyanide is measured in this instrument by a ligand-exchange gas diffusion technique coupled with amperometric detection in accordance with the appropriate EPA and ASTM methods. This non-distillation technique provides an accurate cyanide measurement in the presence of thiocyanate, sulfite, and thiosulfate interferences—an issue with other techniques.
OI Analytical also has a CNSolution system for measuring total cyanide. This instrument employs a UV digestion, gas diffusion technique coupled with amperometric detection. The CNSolution can also be used for post-distillation cyanide samples in a colormetric reaction involving chloramine-T and pyridine/barbituric acid reagents, which is followed by spectrophotometric measurements.
For those situations where users want to measure the potential content of cyanide in water where online instrumentation is not available, a Vacu-Vial Test Kit (K-3803) from CHEMetrics, Calverton, Va., can be used to measure cyanide concentrations up to 0.4 ppm (mg/l). Unit dosages of reagent are sealed under vacuum in the company’s proprietary self-filling ampoules, which eliminates the need to measure and mix chemicals, simplifies the testing, and enhances the reagent’s shelf life. The kit employs the isonicotinic/barbituric acid methodology for analyzing cyanide. Total test time per sample is about 20 min.
