Journal of Chromatography A, 887 (2000) 489–496 www.elsevier.com / locate / chroma Analysis of hydroquinone and some of its ethers by using capillary electrochromatography * Claudia Desiderio, Luigia Ossicini, Salvatore Fanali Istituto di Cromatografia del Consiglio Nazionale delle Ricerche, Area della Ricerca di Roma, P .O. Box 10, 00016 Monterotondo Scalo, Rome, Italy Abstract Capillary electrochromatography (CEC) was used for the analysis of relevant compounds in cosmetic preparation. Hydroquinone (HQ) and some of its ethers (methyl-, dimethyl-, benzyl-, phenyl-, propyl-HQ derivatives) were analyzed by using an octadecylsilica (ODS) stationary phase packed in fused-silica capillary (100 mm I.D.; 30 cm and 21.5 cm total and effective lengths, respectively). 20 mM Ammonium acetate pH 6–acetonitrile (50–70%) were the mobile phases used for the experiments. The acetonitrile (ACN) content strongly influenced the resolution of the studied compounds as well as the efficiency and the retention factor. Baseline resolution for the studied analytes was achieved at both the lowest and the highest percentage of ACN, the last 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 areas and peak areas ratio (A / A ) was found. The calibration graphs were linear in the sample internal standard concentration range studied (5–90 mg / 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 of two additional peaks (not identified).  2000 Elsevier Science B.V. All rights reserved. Keywords: Electrochromatography; Hydroquinone 1. Introduction present in analyzed skin-toning creams [1]. Thus the analytical determination of HQ and its derivatives in Hydroquinone (HQ) is a compound mainly used cosmetics is very important for the human health as antioxidant in the photography industry as well as protection and consumers safeguarding. depigmenter agent in cosmetic products such as skin- Several analytical methods have been so far used toning creams. The HQ mechanism of action in the for the analysis of HQ in toning creams including biological process is based on the inhibition of high-performance liquid chromatography (HPLC), melanin formation and due to the toxicological spectrophotometry, thin layer chromatography effects of HQ, it can cause dermatitis, EU regulations (TLC), micellar electrokinetic chromatography allow its content in cosmetics within the 2% (w/w) (MEKC) etc. [1–7]. level. It has shown that HQ and some of its Capillary electrochromatography (CEC) is a re- derivatives (not allowed by European Directive) were cent analytical technique performed in fused-silica capillaries packed with chromatographic particle materials immobilized into the column by an inlet *Corresponding author. Tel.: 139-6-9067-2256; fax: 139-6- and an outlet frits. In CEC both the electrophoretic 9067-2269. E-mail address: fanali@nserv.icmat.mlib.cnr.it (S. Fanali) and chromatographic mechanism are combined and 0021-9673 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0021-9673(99)01197-8