Voltammetric assay of the anthelmintic veterinary drug nitroxynil in bulk form and formulation at a mercury electrode

The electrochemical behavior of the anthelmintic veterinary drug nitroxynil at the mercury electrode was studied in a series of Britton-Robinson universal buffer of pH 1.9–11 containing 20% (v/v) ethanol using dc-polarography cyclic voltammetry and controlled-potential coulometry. The voltammograms exhibited two irreversible cathodic steps over the pH range 1.9–10.2; the height of the first step is double that of the second one. Controlled-potential coulometry in the B–R universal buffer of pH 1.9–10 at a mercury pool working electrode revealed the consumption of four and two electrons via the first and second reduction steps, respectively, which attributed to reduction of the NO2 group to the hydroxylamine stage (first step), and then to the amine stage (second step). Three voltammetric analytical procedures including dc-polarography, differential-pulse adsorptive stripping voltammetry and square-wave adsorptive stripping voltammetry were optimized for the direct determination of bulk nitroxynil. The three proposed procedures were applied for analysis of bulk nitroxynil with limits of detection of 3 × 10−5, 1.31 × 10−8 and 8.4 × 10−10 M and limits of quantification of 1 × 10−5, 4.36 × 10−8 and 2.80 × 10−9 M, respectively. The three procedures were successfully applied to the determination of nitroxynil in formulation (Dovenix, 25% nitroxynil injection solution) without the necessity for sample pretreatment and/or time-consuming extraction steps prior to the analysis.