Two methods for monitoring the photodecomposition of sodium nitroprusside in aqueous and glucose solutions.

The photodecomposition of sodium nitroprusside (SNP) in aqueous and 5% glucose solutions results in the accumulation of cyanide and ferricyanide ions. Methods for the determination of these ions in such solutions have been devised. The continuous-flow method for cyanide involved the generation of cyanogen chloride, ClCN, by oxidation with chloramine T and subsequent reaction of the ClCN with barbituric acid and pyridine to produce a chromophore measurable by spectrophotometry at 580 nm. This cyanide method had a detection limit and sensitivity of 10-12 mumol/L and 1.40 X 10(-3) absorbance units (AU)/mumol/L, respectively, with a working concentration range of 0-800 mumol/L. This method employed mild reaction conditions, pH = 4.1, which rendered it suitable for use in time-course studies of cyanide production from SNP solutions exposed to 366 nm UV light. A simple method for the determination of ferricyanide in SNP solutions was developed which involved the addition of a 1% FeSO4 X 7 H2O in 1% H2SO4 reagent to the SNP solutions under test followed by spectrophotometry at 750 nm. The detection limit and sensitivity of the method were 2-3 mumol/L and 4.05 X 10(-3) AU/mumol/L, respectively, with a working concentration range of 0-100 mumol/L. This method was considered suitable for use as a quality control test of SNP solutions close to the site of their clinical use.