Determination of thioglycolic acid in cosmetics by capillary electrophoresis

A new and simple method for the accurate determination of thioglycolic acid (TGA) in cosmetics was developed using capillary electrophoresis (CE) with diode array detection at 236 nm. The CE separation was performed on an uncoated fused silica capillary with a separation buffer solution containing 300 mmol L-1 tri-sodium phosphate and 0.5 mmol L-1 cetyltrimethylammonium bromide at a voltage of 5 kV. Both the intra- and inter-day precisions of the method were 1.4%. The calibration curve between the corrected peak areas and the concentrations of the TGA was linear within the concentration range of 0.006-1.0 mg mL(-1) with a correlation coefficient (r) of 0.9998. The limit of detection and limit of quantitation were 0.002 mg mL(-1) (SIN= 3) and 0.006 mg mL(-1) (SIN= 10), respectively. The average recoveries at the spiked levels of 0.125, 0.250 and 0.500 mg mL(-1) were 96.9%, 1023% and 94.0% with the relative standard derivations of 2.1%, 3.9% and 2.2%, respectively. The method was cross-validated by both high performance liquid chromatographic and ion chromatographic method. Eighty-five commercial depilatory creams and hair-treatment products were analyzed with satisfactory results. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.