Cyanides & Thiocyanate in Soils
Aliquots of dried and ground soil are extracted into 1M sodium hydroxide.
Free cyanide: Automated acid distillation followed by colorimetric development with chloramine-T and pyridine/barbituric acid. Intensity of colour at 610nm is measured.
Total cyanide by UV decomposition of complex bound cyanides with measurement of resulting free cyanide as above.
Complex cyanide determined by difference.
Thiocyanate is converted to cyanogen chloride which reacts with chloramine-T and 1.3-dimethylbarbituric acid/isonicotinic acid. Intensity of colour measured at 600nm.
