Electrochemistry of the nitroprusside ion. From mechanistic studies to electrochemical analysis
The electrochemical reduction of the nitroprusside ion (NP) was examined by differential-pulse polarography and square-wave voltammetry. The effect of pH on the electrochemical behaviour of NP was studied and experimental evidence for the occurrence of adsorption of the products of the first one-electron reduction of NP is shown. Owing to the adsorption of these products, which are the reactants in the second reduction step of NP, the peak current of the second process is highly enhanced compared with that of the first process, especially at low concentration levels (< 1 × 10–5 mol dm–3). For acidic solutions the enhancement is considerably higher than at pH 7. A surface reaction leading to the regeneration of the reactants of the second reduction process can be advanced as a possible explanation. Square-wave cathodic stripping voltammetry with adsorptive accumulation was used for the determination of NP. The detection limit depends on the square wave parameters and can be as low as 2.3 nmol dm–3 for a delay time of 60 s.