Selective voltammetric determination of α-lipoic acid on the electrode modified with SnO2 nanoparticles and cetyltriphenylphosphonium bromide

Abstract

Sensitive voltammetric method for α-lipoic acid determination based on glassy carbon electrode (GCE) modified with SnO2 nanoparticles (SnO2 NP) dispersion in cetyltriphenylphosphonium bromide (CTPPB) (SnO2 NP-CTPPB/GCE) has been developed. The comparison to other surface active compounds as dispersive agents has been performed. The electrodes surface has been characterized by scanning electron microscopy, electrochemical impedance spectroscopy, cyclic voltammetry, and chronoamperometry. Statistically significant decrease of charge transfer resistance (10.8 ± 0.4 kΩ vs. 181 ± 7 kΩ for GCE and 71 ± 3 kΩ for SnO2 NP-H2O/GCE) and higher effective surface area (13.7 ± 0.2 mm2 vs. 8.2 ± 0.3 mm2 for GCE and 12.1 ± 0.2 mm2 for SnO2 NP-H2O/GCE) has been obtained for SnO2 NP-CTPPB/GCE. α-Lipoic acid oxidation on SnO2 NP-CTPPB/GCE is a two-electron diffusion-controlled pH independent process leading to β-lipoic acid formation. Under conditions of differential pulse voltammetry in Britton–Robinson buffer pH 4.5, the linear dynamic ranges are 0.50–50 and 50–400 μmol dm−3 of α-lipoic acid with the limits of detection and quantification of 0.13 and 0.43 μmol dm−3, respectively. The method developed has been successfully applied for the pharmaceutical dosage form analysis.