Square-wave adsorptive stripping voltammetric behaviour of entacapone at HMDE and its determination in the presence of surfactants

The objective of the present work is to develop a voltammetric method for the determination of entacapone based on the enhancement effect of Tween 20. Addition of neutral surfactant (Tween 20) to the entacapone containing electrolyte enhanced the reduction current signal while anionic surfactant (sodium lauryl sulphate) and cationic surfactant (cetrimide) showed an opposite effect. The reduction process was irreversible over the entire pH range studied (2.5–12). The mechanism of reduction has been postulated on the basis of controlled potential electrolysis and coulometry. The current–concentration plot was rectilinear over the range from 5 × 10−4 mol L−1 to 1.8 × 10−5 mol L−1 with a correlation coefficient of 0.996 for differential pulse voltammetry (DPV) and 1.6 × 10−4 mol L−1 to 1.6 × 10−5 mol L−1 with correlation of 0.999 M for square ware voltammetry (SWV) in Britton Robinson buffer at pH 2.5. The lower limit of quantification (LOQ) and the lower limit of detection (LOD) were found to be 0.42 ng mL−1 and 0.13 ng mL−1 respectively. The analysis of entacapone in its pharmaceutical formulation exhibited the mean recovery of 99% for the reduction peak.