Reverse-phase liquid chromatographic determination of α-lipoic acid in dietary supplements using a boron-doped diamond electrode.
A fast liquid chromatographic separation, coupled with sensitive and straightforward detection using a boron-doped diamond (BDD) electrode, was developed and validated for the determination of α-lipoic acid in dietary supplement samples. The analysis was carried out using a reversed phase C18 (150 mm × 4.6 mm, 5 μm) column with a mobile phase consisting of a 1:1 (v/v) ratio of 0.05 M phosphate solution (pH 2.5):acetonitrile, at a flow rate of 1.0 mL/min. The detection potential obtained from hydrodynamic voltammetry was 1.05 V vs. Ag/AgCl. Under optimized conditions, the chromatographic separation was performed in less than 5 min, a good linear relationship was obtained between the current and the α-lipoic concentration within the range of 0.01-60 μg/mL (correlation coefficient of 0.9971), and a detection limit of 3.0 ng/mL was determined. Furthermore, this method was successfully applied to determine α-lipoic acid concentrations in selected commercial dietary supplement samples. The recovery of α-lipoic acid in spiked samples at 0.5, 5.0 and 30 μg/mL ranged from 94.4% to 103.6% with a relative standard deviation (RSD) of between 1.2% and 3.7%. In real samples, this developed methodology produced results that were highly correlated with the standard HPLC-UV approach. Therefore, the present method can be used for fast, selective and sensitive quantification of α-lipoic acid in dietary supplements.
Department of Chemistry, Faculty of Science, Srinakharinwirot University, Sukumvit 23 Rd., Wattana, Bangkok 10110, Thailand. weena@swu.ac.th
Weena
W
Siangproh
Poomrat
P
Rattanarat
Orawon
O
Chailapakul
D001895:Boron / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D056148:Chromatography, Reverse-Phase / Q000379:methods*; D018130:Diamond / Q000737:chemistry*; D019587:Dietary Supplements / Q000032:analysis*; D055664:Electrochemical Techniques; D004566:Electrodes; D057446:Hydrodynamics; D010084:Oxidation-Reduction; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D008063:Thioctic Acid / Q000032:analysis* / Q000737:chemistry
D008063:Thioctic Acid; D018130:Diamond; D001895:Boron