Spectrophotometric determination of sodium nitroprusside and its photodegradation products.

A specific spectrophotometric method of analysis for sodium nitroprusside was developed utilizing the molar absorptivity values at the maxima appearing in the electronic spectrum at 394 and 498 nm that may be attributed to metal d leading to pi* NO transitions. These measurements appear to be indicative of the unaltered nitroferricyanide complex. A reaction sequence is postulated for aqueous solutions of nitroprusside exposed to normal artificial light. Evidence suggests that one species in the sequence is nitroferricyanide in a higher energy state but with the nitrosyl moiety still present in the coordination sphere, which exhibits an increased molar absorptivity at 394 nm. The molar absorptivity at the 498-nm maximum remains unchanged. Corroborating polarographic data are presented.