Cyanide

This method is used for the determination of cyanide in water and wastewater. The EPA range of this method is 5 to 500 µg/L. However, this method is also applicable to other ranges.

Summary

Cyanide is released from cyanide complexes by ultraviolet digestion and on-line distillation. The liberated hydrogen cyanide is converted to cyanogen chloride by reaction with chloramine-T at a pH less than 8. The cyanogen chloride then reacts with pyridine-barbituric acid reagent to form a red colored complex. The complex is measured at 570 nm.

Limitations

 Interferences are eliminated or reduced by distillation prior to color formation. Samples containing sulfides should be treated to remove the sulfide as outlined in "Sample Handling and Preservation". Oxidizing agents that decompose cyanides are removed by the addition of ascorbic acid. Thiocyanates produce a positive interference when they are decomposed by the ultraviolet digestion.

 Online distillation

Offline distillation (recommended)