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J. Cosmet. Sci., 63, 321–331 (September/October 2012) 321 Simultaneous determination of 13 components in oxidative hair dyes by high-performance chromatography using an ion-pair reagent YING LAI, HONGHUI WANG, QINGMU DONG, HEXIU CHEN, RUI LIN, and YANPING CAI, Technology Center of Xiamen Entry-Exit Inspection and Quarantine Bureau, Xiamen 361026, People’s Republic of China. Accepted for publication March 12, 2012. Synopsis A reliable high-performance liquid chromatography (HPLC) method was developed for the simultaneous deter- mination of 13 dye intermediates, including benzenediamines, aminophenols, benzenediols, naphthalenediol, and diaminopyridine, in oxidative hair dyes. Samples were extracted with 50% ethanol by adding sodium dithionite to prevent oxidation. The infl uences of buffer type, buffer pH, ion-pair reagent, and elution gradient were studied. A C18 column with aqueous compatibility and acetonitrile–citric acid mobile phase system (pH 2.6) with sodium 1-octanesulfonate as ion-pair reagent were selected for the separation of target com- pounds. Detection was performed by a diode array detector, (DAD) and two different wavelengths (280 and 331 nm) were used for quantifi cation. Results showed that 13 dye intermediates got good separation within 25 min. The detection limits of these compounds were in the range of 0.2–2 mg/l. The calibration curves were linear within 2–500 mg/l with 0.999 as a typical correlation coeffi cient. The recoveries of target compounds in hair dyes ranged from 81.7% to 102.0% with four addition levels. The method described was validated by fi ve different laboratories and successfully applied to the analysis of commercial oxidative hair dyes. INTRODUCTION Oxidative hair dye, the most widely used permanent dye, usually contains a mixture of aromatic compounds including benzenediamines, aminophenols, benzenediols, naphtha- lenediol, and diaminopyridine. Such substances are of great health concern due to their mutagenic or even carcinogenic activity (1,2). The use of these compounds in hair dyes is regulated by legislation in many countries. Therefore, a simple and rapid method for the determination of these dye intermediates in hair dyes is of utmost importance. Several methods have been developed for the analysis of dye intermediates in hair dyes, including thin layer chromatography (TLC) (3,4), high-performance liquid chromatography (HPLC) (5–11), high performance liquid chromatography-mass Address all correspondence to Ying Lai at laiy@xmciq.gov.cn.