National Institute for Occupational Safety and Health

“ Transfer the solution to be measured to a 50-mL beaker. Immerse the cyanide ion electrode and reference electrode in the sample and start the magnetic stirrer. With the magnetic stirrer on, allow the potential reading to stabilize. Record the mV reading. NOTE 1: Potential readings are a function of temperature. Measure samples and working standards at the same temperature (± 2 °C) . NOTE 2: The cyanide electrode will malfunction if chloride, iodide and bromide ions, which form insoluble silver salts, are present in sufficient quantity. ”

“ If sulfide ion has not been removed completely, add more cadmium carbonate. Avoid a large excess of cadmium carbonate and long contact time with the solution. When a drop of liquid no longer discolors a strip of lead acetate paper, filter the sample through a small plug of glass wool in a Pasteur pipette and proceed with the analysis. ”

“ ACCURACY:
± 20.0%
25 mL 0.1 N KOH; 30 min
2 mL 0.1 N KOH; dilute to 25 mL with 0.1 N KOH
APPLICABILITY: The working range (as CN -) is 0.5 to 15 mg/m 3 for a 90-L air sample or 5 to 20 mg/m 3 for a 10-L air sample.
INTERFERENCES: Sulfide, chloride, iodide, bromide, cadmium, zinc, silver, nickel, cuprous iron and mercury interfere. In humid atmospheres, some particulate cyanide collected on the filter will liberate hydrogen cyanide which will be trapped in th e bubbler [2] . The method cannot distinguish between HCN formed in this manner and HCN originally present in air. ”