Limitations of the cyanide electrode for use in plasma and whole blood

Although the cyanide ion-specific electrode has been used for the measurement of cyanide in biologic fluids, its validity has not been documented under these conditions. Therefore, we analyzed 60 paired samples of blood and plasma in a blinded fashion and compared the cyanide ion concentrations obtained from the ion-specific electrode with those obtained from a standard chemical assay. There was poor correlation between results in plasma samples (r = .52, n = 26) and no correlation in whole blood (r = .02, n = 34). Until refinements of the electrode technique are made, this method cannot be recommended for the measurement of cyanide in biologic fluids.