An improved method for simultaneous square-wave voltammetric determination of amlodipine and enalapril at multi-walled carbon nanotubes paste electrode based on effect of cationic surfactant

A reproducible and sensitive analytical procedure has been developed for the simultaneous determination of amlodipine (AML) and enalapril (ENP) by square-wave voltammetry using a multi-walled carbon nanotubes paste electrode in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The experimental parameters, such as concentration and type of cationic surfactant, pH of Britton–Robinson (BR) buffer, and amount of carbon nanotubes in the paste were optimized. The anodic peak potentials of AML and ENP at multi-walled carbon nanotubes paste (MWCNTsP) electrode were found to be 0.790 and 1.21 V [vs. Ag/AgCl (3.0 mol L−1 KCl)], respectively by square-wave voltammetry, whereas at a GCE was 0.753 V for AML and no peak potential was observed for ENP. In addition, the surfactant has been found to influence the electrochemical determination by the way enhanced of better repeatability of analytical signals for AML and it was possible the simultaneous direct determination of AML and ENP on the MWCNTsP electrode, without pre-concentration of the antihypertensives into the working electrode before each determination. Under optimized conditions in Britton–Robinson buffer (pH 6.0) containing 10 μmol L−1 CTAB, linear calibration curves were obtained in the range of 0.58–5.9 μmol L−1 for AML and 2.0–57 μmol L−1 for ENP, which shows adequate for the quantification in real samples. The limit of detection was 0.049 and 0.81 μmol L−1, respectively, for AML and ENP. The proposed method was used to estimate the amounts of individual and simultaneous antihypertensives in pharmaceutical formulations. Statistical comparison between the results obtained by this method and those obtained by the chromatography method was carried out and no significant difference was observed.