Plasma free cyanide and blood total cyanide: a rapid completely automated microdistillation assay.

Techniques are presented which provide direct measurement of both free cyanide (CN-) in plasma and total CN- in whole blood. Loss of total CN- from blood is prevented by conversion to cyanmethemoglobin. Both free and total CN- are assayed by a completely automated method providing readout 17 minutes after sampling. No prior isolation technique is required and sensitivity is adjustable to cover a broad range of CN- concentrations from 1 to 4000 uM. Precision of blood CN- values from 2 to 2500 uM is within +/- 2.3%. No interference results from thiocyanate or thiosulfate at a concentration of approximately 1 mM.