An Electroanalytical Approach to Brimonidine at Boron Doped Diamond Electrode Based on Its Extensive Voltammetric Study

Abstract

An extensive electrochemical study of brimonidine at boron doped diamond electrode (BDDE) was done by applying cyclic voltammetry (CV) and square-wave voltammetry (SWV) in sulfuric acid of different concentrations (pH ranged from 0.6 to 1.6), and in BR buffer (pH ranged from 2.0 to 9.0). It was found that the reduction of brimonidine occurred in a one-step quasi-reversible mechanism, involving the transfer of two electrons and two protons. The reduction process took place at the quinoxaline ring and the corresponding mechanism of reduction was confirmed to be the same as for the other quinoxaline derivatives. The nature of the electrode process was found to be diffusion controlled in acid medium, while in a more alkaline medium a certain degree of adsorption was noticed. Based on this study, two sensitive voltammetric methods, differential pulse (DPV) and square wave (SWV) were developed, fully validated and suggested for rapid electroanalytical determination of low concentrations of brimonidine. The linearity was achieved within the concentration range from 2x10-6 M to 3x10-5 M for DPV (LOD=6.31x10-7 M, LOQ=2.1x10-6 M) and from 5x10-7 M to 1.5x10-5 M for SWV (LOD=1.28x10-7 M, LOQ=4.28x10-7 M). The methods were applied for brimonidine determination in pharmaceutical dosage form, eye drops. The obtained good recoveries suggested these simple and accurate methods for quality control of brimonidine in dosage form. Due to its high sensitivity, the SWV method could be a good alternative for determination of low concentrations of brimonidine, even in biological samples.