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.
Keywords: Alpha lipoic acid, food supplements, HPLC, pulsed amperometric detection, gold electrode.
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