Adsorptive stripping voltammetric assay of phenazopyridine hydrochloride in biological fluids and pharmaceutical preparations

A sensitive method for the measurement of phenazopyridine hydrochloride (PAP) by differential pulse polarography (DPP) based on adsorptive stripping technique, using a hanging mercury drop electrode (HMDE) is described. The voltammetric peak is obtained at −0.760 V, which corresponds to the reduction of the azo group in Britton–Robinson buffer. The redox behaviour is reversible. Optimum conditions were found to be: accumulation potential −50 mV (vs. Ag/AgCl), accumulation time 60 s, scan rate 5 mV s−1, pulse amplitude −100 mV and supporting electrolyte Britton–Robinson buffer (0.04 M, pH=11). The relative standard deviation (at 20 ng ml−1 level) was ±0.6% for six measurements. The calculated detection limit was 0.0299 ng ml−1 with a 60-s accumulation time. The applicability of such a method was evaluated through the assay of PAP in human plasma and urine samples after a simple extraction procedure and in pharmaceutical preparation. The mean recovery was 97±2 (100 ng ml−1 plasma).