Electrochemical determination of captopril at boron-doped diamond thin film electrode applied to a flow injection system

A boron-doped diamond thin film (BDD) electrode was first used to study the electroanalysis of captopril in phosphate buffer (pH = 9) by several techniques such as cyclic voltammetry, hydrodynamic voltammetry and flow injection with amperometric detection. Cyclic voltammetry was used to study the reaction as a function of concentration of analyte. The results were compared with a glassy carbon (GC) electrode at the same condition. Captopril undergoes irreversible reaction at both electrodes. However, the BDD electrode provided highly reproducible, well-resolved cyclic voltammogram and higher signal-to-background (S/B) ratio comparing with GC electrode. Linear range from 50 M to 3 mM and detection limit of 25 muM (S/B approximate to 3) were obtained from the BDD electrode using cyclic voltammetry. The potential sweep rate dependence of captopril oxidation (peak currents for 1 mM captopril linearly proportional to nu(1/2), within the range of 0.01 to 0.3 V s(-1)) indicates that the oxidation current is diffusion controlled with negligible adsorption on the BDD surface. The flow injection experiments of the BDD electrode at the concentration from 0.5 to 100 muM provided a linear dynamic range and very low detection limit of 10 nM were obtained (S/N approximate to 3). In addition, the determination of captopril in the commercial available tablets by flow injection system with amperometric detection at diamond electrodes has also been investigated. The results show very good precision (1.21-2.15%). (C) 2003 Elsevier Science B.V. All rights reserved.