Quantification of Alpha Lipoic Acid in Pharmaceutical Products by HPLC with Pulsed Amperometric Detection at a Gold Electrode

Background: Alpha-lipoic acid (ALA) has become a common ingredient in food supplements and multivitamin formulas. ALA is widely used as therapy for preventing diabetic polyneuropathies, scavenges free radicals, and restores intracellular glutathione levels. This study aimed to develop a simple and fast analytical method to determine ALA content in dietary supplements using highperformance liquid chromatography with pulsed amperometric detection (HPLC PAD). Methods: ALA was analyzed by HPLC in a mobile phase composed of 25 mmol/L potassium phosphate in 50% (v/v) acetonitrile (pH 4.0) and PAD at a gold electrode (vs. solid-phase hydrogen reference electrode). The PAD cycle was performed by applying a detection potential (E1) of +0.7 V for 0.4 s, an oxidation potential (E2) of +1.0V for 0.4 s and a reduction potential (E3) of -0.2 V for 1.2 s. Results: The runtime method was shown a rapid procedure for the analysis of α-lipoic acid. The sampling rate of 8 injections per hour was attained and measurements of the reproducibility of successive injections (20 μL) showed an RSD of 1.89% for 16 successive injections. The method presented low quantification limit of 0.21 mg/L. The industrialized ALA-based supplements ranged from to 97.8 to 104.1%, while manipulated capsules ranged from 69.2 to 95.4%. Conclusion: Electrochemical detector has been presented as an effective alternative for ALA determination, which has weakly UV-absorbing. This detection has the benefits of sensitivity, simplicity and low costs. The developed HPLC-DAD method proposes to be analytical tool applicable to quality control of ALA supplements.