Electro-Oxidation Mechanism and Direct Square-Wave Voltammetric Determination of Lidocaine With a Carbon-Paste Electrode

Background: Lidocaine hydrochloride (LH) is one of the most extensively used local anesthetics and peripheral analgesics. Availability of a simple and sensitive assay method for this analyte in pharmaceutical preparations as well as development of new voltammetric detectors that can be applied in chromatographic systems for determination of this analyte in biological samples are of great importance.

Objectives: In this study, a square-wave voltammetric (SWV) determination of LH at a bare carbon-paste electrode (CPE) was reported. Moreover, the oxidation mechanism for LH molecule at this electrode was investigated.

Materials and Methods: The SW voltammogram of LH solution at CPE showed a well-defined peak between +0.80 and +0.88 V depending on a scan rate in potassium nitrate (KNO₃) solution. Different chemical and instrumental parameters influencing the voltammetric response, such as the pH level and scan rate were optimized for LH determination.

Results: A linear range of 8.0 - 1000.0 ?mol L^-1 (r² = 0.999) was obtained. The limit of detection (LOD) was 0.29 ?mol L^-1. The relative standard deviations of 2.1% obtained for 0.8 800 ?mol L^-1 solution of LH indicated a reasonable reproducibility of the method.

Conclusions: The results of this study show that LH in different pharmaceutical preparations could be determined with good reliability. In addition, the results reveal that the equal numbers of electrons and protons are involved in the oxidation of LH and the irreversible oxidation of an analyte was performed via amine groups of LH molecule.