Method 335.2

Total Cyanide (Titrimetric; Spectrophotometric)

This method is for the determination of cyanide in drinking, surface and saline waters, domestic and industrial wastes.  The titration procedure using silver nitrate with p-dimethylamino-benzal-rhodanine indicator is used for measuring concentrations of cyanide exceeding 1 mg/L (0.25 mg/250 mL of absorbing liquid). The colorimetric procedure is used for concentrations below 1 mg/L of cyanide and is sensitive to about 0.02 mg/L.

Cyanide as hydrocyanic acid (HCN) is released from cyanide complexes by means of a reflux-distillation operation and absorbed in a scrubber containing sodium hydroxide solution. The cyanide ion in the absorbing solution is then determined by volumetric titration or colorimetrically. In the colorimetric measurement, the cyanide is converted to cyanogen chloride, CNCl, by reaction with chloramine-T at a pH < 8 without hydrolyzing to the cyanate. After the reaction is complete, color is formed on the addition of pyridine-pyrazolone or pyridine-barbituric acid reagent. The absorbance is read at 620 nm when using pyridine-pyrazolone or 578 nm for pyridine-barbituric acid. To obtain colors of comparable intensity, it is essential to have the same salt content in both the sample and the standards. The titrimetric measurement uses a standard solution of silver nitrate to titrate cyanide in the presence of a silver sensitive indicator.

After sample collection, test the sample for the presence of oxidizing agents using KI-starch paper.  If oxidizers are present, add ascorbic acid until a drop test is negative and then add 0.06 g of additional ascorbic acid.

Oxidizing agents can destroy cyanides during storage.  Sulfide can complex with cyanide in the sample or distillate.  Fatty acids, carbonate, aldehydes, glucose/sugars, and sulfur-containing compounds can cause interferences during the distillatioin.  

(EPA: Office of Water)


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Method Data

Hold Times, Preservatives, Preps, Collection, Analytical & Documentation
Holding Time:   14 days from sample collection to analysis.
Preservatives:   Adjust to pH >12 with sodium hydroxide and store at 4°C.
Required Preps:   1 L HDPE bottle with Teflon-lined lid
Collection Method:   Grab sampling
Analytical Methodology:   Spectrophotometric or Titrimetric
Documentation:   335.2

Analyte List*

Analyte Formula CAS Number Detection Limit

* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.