Thiocyanatein BiologicalFluids,and Its

A colorimetricprocedure for determination of small amounts of cyanide and thioCyanate, in-volvingthe synthesisof a pyridinedyestuffby the reactionof pyridineand an aromatic amine, has been simplifiedforthe estimation of thiocyanate alone in biologicalfluids.Replacement of benzi-dine with p-phenylenediamine in the colorimetric reactionhas both improved the precisionof the analyticalprocedure and avoided a carcinogenic hazard. This method has been used to followthe decrease in plasma thiocyanate associated with abstinence from cigarettesmoking, and itssub-sequent increase upon resumption. It has also been used to measure the plasma and urinary thiocya nate concentrations of patients suffering from the particular toxic arnblyopias-tobacco amblyopia and Leber’s hereditary optic atrophy-believed to be associated with cyanide toxicity, and to follow the increased thiocyanate concen-traticins that accompany significant improvements in the patients ’ vision brought about by various treatments. Additional Keyphrases tobacco amblyopia Leber’s hereditary optic atrophy #{149}cyanide toxicity cyanide-thiocyanat,e conversion #{149}effects of smoking p-phenylenediamine reagent #{149}vitamin B12 therapy cystine therapy Cyanide toxicity has been implicated as a pos-sible cause of the visual failure in patients suffer-ing from the toxic amblyopias, particularly tobacco amblyopia and Leber’s hereditary optic atrophy (1-5). The source of the cyanide may be tobacco smoke and it has been suggested that these pa-tients have a decreased ability to convert cyanide to its maj or metabolite, thiocyanate (6). Because of difficulties encountered in the esti-mation of cyanide, at the normally very low con-centrations encountered in biological materials, we decided that the estimation of thiocyanate in plasma and urine would form a suitable index of altered cyanide metabolism