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R9 Laboratory SOP 532
CYANIDE ANALYSIS
Summary
This method is for the determination of cyanide in drinking, surface, and saline waters as well as domestic and industrial waste. This SOP is based on EPA Method 335.4.
The applicable range is 10 to 100 mg/L cyanide. The calibration range can be extended for high level samples through dilution either before or after the distillation procedure. This method is based upon a modification of EPA Method 335.4, in which sample and reagent volumes are reduced by a factor of 6/50. The volume reduction has several advantages, including the generation of significantly less waste and reducing the space and labor required for the distillation process.
Samples are preserved to pH 12 in the field. Inside a micro-distillation apparatus, the basic samples are acidified, which converts free cyanide and most cyanide complexes to hydrogen cyanide (HCN). The HCN is distilled from the sample and trapped in a 0.25M NaOH scrubber solution. The scrubber is analyzed for cyanide colorimetrically by flow injection analysis. The colorimetric determination is based upon the reaction of cyanide with chloramine-T at pH<8 to form cyanogen chloride, which subsequently reacts with a pyridine-barbituric acid reagent to form a red-blue dye. The absorbance of the dye is monitored at 570nm and is directly proportional to the concentration of cyanide in the scrubber solution. The system is calibrated by analyzing cyanide calibration standards.