Voltammetric determination of cyanide and thiocyanate in small biological samples

Practical methods for the quantitative measurement of cyanide and thiocyanate content in small biological samples are presented. The basis of the procedures is electrochemical determination of CN- with a silver rotating disk electrode at 90 mV, relative to the Ag/AgCl reference electrode, or with a dropping mercury electrode in differential pulse mode at -240 mV. Thiocyanate is oxidized to CN- with permanganate under controlled conditions prior to its analysis. Endogenous cyanide and cyanide from SCN- oxidation are recovered, separately, by volatilization and trapping. Emphasis is placed on careful handling of specimens prior to analysis. Precautions include a provision for sequestering cyanide in storage, the use of an antioxidant, and an avoidance of the spontaneous sulfide formation from proteins that occurs in even mildly alkaline solutions.