Fluorometric determination of cyanide in biological fluids and pyridoxal

Investigations of the physiological disposition of cyanide during thiosulfate therapy has necessitated the development of a convenient and sensitive method for cyanide analysis. A fluorometric method involving the catalytic conversion of pyridoxal to 4-pyridoxylactone was adapted for use with biological fluids by employing microdiffusion analysis. The presence of the cyanide antagonist, sodium thiosulfate, interferes with the formation of the fluorophore. In order to circumvent this interference, the pH of the diffusion media was altered to selectively diffuse cyanide. After testing various acidifying agents, an acetate buffer (pH = 5.2) was determined to be satisfactory. The fluorometric method was then correlated with the classical colorimetric procedure by an in vivo study. Blood from mice treated with sodium nitrite and sodium thiosulfate, prior to receiving potassium cyanide, was analyzed by both procedures and no significant difference was demonstrated between the results of the two methods of analysis.