alpha-Lipoic acid in dietary supplements: development and comparison of HPLC-CEAD and HPLC-ESI-MS methods.
Alpha-lipoic acid is an antioxidant used both in the prevention and treatment of various oxidative stress related diseases. It is an important constituent of some dietary supplements and can also be found in plant and animal sources. A rapid method for the determination of alpha-lipoic acid in dietary supplements based on high performance liquid chromatography coupled with a coulometric electrode array detector (CEAD) and an electrospray ionization mass spectrometer (ESI-MS) was developed. First, alpha-lipoic acid was extracted with methanol by sonication, chromatographic separation was then achieved by isocratic elution [acetonitrile/methanol/50mM potassium dihydrogen phosphate (pH 3, adjusted with phosphoric acid): 350/65/585, v/v/v] using an ACE 3-C-18 column at a flow rate of 0.45 ml/min. alpha-Lipoic acid was detected by means of a CEAD at +300, +400, +450, +500, +550, +600, +650, and +700 mV against palladium reference electrodes. For ESI-MS detection (negative mode), the composition of the mobile phase was changed to 0.1% acetic acid in water/acetonitrile 55:45, v/v applying a flow rate of 0.2 ml/min. The presented methods were utilized to determine the alpha-lipoic acid content in six dietary supplements. The results of both detection modes were in good correlation.
Durrani
Arjumand I
AI
Institute of Analytical and Food Chemistry, University of Vienna, Währinger Strasse 38, A-1090 Vienna, Austria.
Schwartz
Heidi
H
Schmid
Walther
W
Sontag
Gerhard
G
D000975:Antioxidants / Q000032:analysis*; D002138:Calibration; D002851:Chromatography, High Pressure Liquid; D019587:Dietary Supplements / Q000032:analysis* / Q000592:standards; D004566:Electrodes; D016014:Linear Models; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization; D008063:Thioctic Acid / Q000032:analysis*
D000975:Antioxidants; D008063:Thioctic Acid