Determination of free hydrogen cyanide in river water by a solvent-extraction method
The method described for the determination of undissociated hydrogen cyanide in river waters is designed to avoid disturbance of the equilibria between hydrogen cyanide, cyanide ion and complex cyanides during the determination. A small proportion of the hydrogen cyanide present is extracted by equilibrating the sample with 1,1,1-trichloroethane. The extracted hydrogen cyanide is then transferred into sodium pyrophosphate solution, and the determination is completed colorimetrically by a modification of the method of Bark and Higson. The effect of temperature on the extraction has been studied. Extractions can be carried out in the field, and conditions have been established for bringing extracted samples back to the laboratory for colorimetric analysis. The method can be used in the range 0 to 2 mg of hydrogen cyanide l–1 and less than 0·01 mg l–1 is detectable. Satisfactory tests have been carried out on solutions of known hydrogen cyanide content, on solutions of metallic complex cyanides and on river waters containing added cyanide.