Analysis of hydroquinone and some of its ethers by using capillary electrochromatography

Capillary electrochromatography (CEC) was used for the analysis of relevant compounds in cosmetic preparation. Hydroquinone (HQ) and some of its ether s (methyl-, dimethyl-, benzyl-, phenyl-, propyl-HQ derivatives) were analyz ed by using an octadecylsilica (ODS) stationary phase packed in fused-silic a capillary (100 mu m I.D.; 30 cm and 21.5 cm total and effective lengths, respectively). 20 mM Ammonium acetate pH 6-acetonitrile (50-70%) were the m obile phases used for the experiments. The acetonitrile (ACN) content stron gly influenced the resolution of the studied compounds as well as the effic iency and the retention factor. Baseline resolution for the studied analyte s was achieved at both the lowest and the highest percentage of ACN, the la st one providing the shortest analysis time. Mobile phase containing 70% of ACN was therefore used for the analysis of an extract of skin-toning cream declared to contain HQ. Good repeatability of both retention times, peak a reas and peak areas ratio (A(sample)/A(internal) (standard)) was found. The calibration graphs were linear in the concentration range studied (5-90 mu g/ml) with correlation coefficients between 0.9975 and 09991. The analysis of the cosmetic preparation revealed the presence of HQ (1.72%, w/w) and o f two additional peaks (not identified). (C) 2000 Elsevier Science B.V. All rights reserved.