Cyanide nitroprusside test

The cyanide nitroprusside test determines the presence of free sulfhydryl or disulfide compounds in urine samples [1, 3,4]. During the first step of the assay, cyanide reduces any disulfides that are present to free sulfhydryl compounds. In the second step, a reddish color reaction results when the free sulfhydryl groups complex with nitroprusside. A positive result is most usually due to cystine in the urine. Familial cystinuria is among the most common aminoacidurias. Disulfides are also excreted in other metabolic disorders such as homo cystinuria and ji-m e reap lol ac la le - cy s lei ne disulfiduria. Both will also produce positive results according to the following reaction RSH + Na2Fe(CN)5NO (sodium nitroprusside) — chromophore + NO. 

Sakurai, T. 1989. Toxic gas tests with several pure and mixed gases using mice. J. Fire Sci. 7 22-77. Schulz, V. 1984. Clinical pharmacokinetics of nitroprusside, cyanide, thiosulphate and thiocyanate. Clin. Pharmacokin. 9 239-251. 

Procedure. To 6 ml. of saturated NaCl add 2 ml. of the solution to be tested. Then add successively 1 ml. of the sodium nitroprusside solution and 1 ml. of the sodium carbonate-sodium cyanide mixture. Read the optical density against water at 520 m/i. Blanks are prepared in the same manner except that 2 ml. of water is used instead of 2 ml. of the solution to be tested. A standard curve is prepared with known amounts of cysteine or of reduced glutathione. 

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