Determination of Trace Amounts of Lorazepam by Adsorptive Cathodic Differential Pulse Stripping Method in Pharmaceutical Formulations and Biological Fluids

Abstract

A new adsorptive cathodic differential pulse stripping voltammetry method for the direct determination of lorazepam at trace levels in pharmaceutical formulations and biological fluids is proposed. The procedure involves an adsorptive accumulation of lorazepam on a hanging mercury drop electrode (HMDE), followed by reduction of adsorbed lorazepam by voltammetric scan using differential pulse modulation. The optimum conditions for the analysis of lorazepam are pH=2 using Britton‐Robinson (B‐R) buffer, accumulation potential of −0.2 V (vs. Ag/AgCl), and accumulation time of 40 sec. The peak current is proportional to the concentration of lorazepam, and a linear calibration graph is obtained at 0.05–1.15 µg mL−1. A relative standard deviation of 2.41% (n=3) was obtained, and the limit of detection was 0.019 µg mL−1. The capability of the method for the analysis of real samples was evaluated by determination of lorazepam in pharmaceutical preparations and biological (urine and plasma) fluids with satisfactory results.