Determination of Physiological Levels of Blood Cyanide without Interference by Thiocyanate.

Acidification of blood, which is a general pretreatment procedure for cyanide analysis, caused artifactual cyanide formation from thiocyanate. A method for the determination of trace levels of blood cyanide has been developed using headspace gas chromatography with a nitrogen-phosphorus detector and a GS-Q column. By the addition of 30 mmol/l of ascorbic acid, this method eliminated thiocyanate interference. The detection limit was roughly 0.05μmol/l blood (S/N=3). Using this established method, blood cyanide levels were determined for transfusion blood samples from healthy donors, and also plasma thiocyanate levels were determined by the Konig colorimetric method. The artifactually formed cyanide levels, which were obtained by subtraction of the cyanide levels determined in the presence of ascorbic acid from those in its absence, were in proportion to the thiocyanate levels, indicating that plasma thiocyanate is oxidized to cyanide through oxyhemoglobin acidification.