J. Cosmet. Sci., 65, 265–276 (September/October 2014) 265 Determination of zinc pyrithione in shampoos by HPLC and HPLC-MS/MS YU-XIANG GU, QING-HE WANG, ZE-LIN ZHOU, QING LV, and CHENG-HUA MAI, Shanghai Institute of Quality Inspection and Technical Research, Shanghai 200233, People’s Republic of China. Accepted for publication May 23, 2014. Synopsis Methods have been developed for the determination of zinc pyrithione (ZPT) in shampoos using high-performance liquid chromatography (HPLC) and high-performance liquid chromatography-mass spectrometry/mass spec- trometry (HPLC-MS/MS). Samples were washed by water fi rst to remove surfactant and water-soluble impu- rities, then ultrasonic-extracted by acetonitrile–methanol for 30 min, and fi nally analyzed by MG C18 column (250 mm × 4.6 mm, 5 μm) or RP-18e (100 mm × 3 mm, 2 μm) plus APCI-MS/MS. Limits of detection were determined as 0.015% (HPLC) and 0.003% (HPLC-MS/MS), with a limit of quantization of 0.05% and 0.01%, respectively. The recoveries were 85.8–104% (HPLC) and 87.6–107% (HPLC-MS/MS). A good linear relationship was obtained from 3.20 μg·ml-1 to 200 μg·ml-1 (HPLC) and 1.00 μg·ml-1 to 200 μg·ml-1 (HPLC-MS/MS). The proposed methods have been successfully applied to the analysis of ZPT in many sham- poos. The established two methods were rapid and reproducible with low interference. INTRODUCTION Zinc pyrithione (ZPT) was the zinc chelate of 2-pyridinethiol 1-oxide, and it was used as a cosmetic preservatives in the late 1960s. Procter and Gamble Co. discovered the anti- dandruff properties of ZPT fi rst, and it was known as an effective bactericide, fungicide, and algicide through various clinical studies (1,2). Such properties have led to ZPT being extensively used in cosmetics especially as an antidandruff agent in hair care products. Now, it is the most common active ingredient in antidandruff shampoo products. The toxicity of pyrithione salts by various routes of exposure has been studied in several species of animals and has been described previously (3–5). On the basis of research data, the Economic Community (76/768/EEC, now Regulation [EC] No 1223/2009) Council Directive allowed ZPT to be used in cosmetics as a preservative in hair products at 1.0% and other rinse-off products at 0.5%. The ZPT was not allowed in oral hygiene products. For leave-on hair products, it is allowed at 0.1% in cosmetics. In China, Hygienic Stan- dard for Cosmetics allowed ZPT to be used in cosmetics as a preservative in rinse-off Address all correspondence to Yu-Xiang Gu at guyuxiang1@gmail.com.

JOURNAL OF COSMETIC SCIENCE 266 products at 0.5% and as an antidandruff in rinse-off products at 1.5%. Also, ZPT was not allowed in oral hygiene products. The use of ZPT in antidandruff preparations required analytical techniques for quality control during manufacture and market supervision. The direct HPLC analysis of ZPT was diffi cult in the past owing to the problematic interaction with reversed-phase pack- ing materials (6). In recent years, attempts to avoid such unwanted interactions have fo- cused upon the improvement of silica stationary phase. Several methods have been developed for detecting ZPT in many types of samples including cosmetics, water, and so on (7–14). For example, Bones et al. improved a method for the determination of ZPT in environmental water samples incorporating online extraction and preconcentration cou- pled with liquid chromatography atmospheric pressure chemical ionization mass spec- trometry. Limits of detection was 18 ng·l-1, with a limit of quantitation of 62 ng·l-1. The percentage recoveries were 72 ± 9% (7). Thomas established a method to determine ZPT in water samples by copper chelate formation and high-performance liquid chromatogra- phy (HPLC)–atmospheric pressure chemical ionization mass spectrometry. The recoveries of the method were 77 ± 17%, the limit of detection was 20 ng·l-1 (8). Nakajima reported a high-performance liquid chromatographic determination of ZPT in antidandruff prep- arations based on copper chelate formation. The calibration graph was linear from 0.1 to 0.5 μg for ZPT. The recoveries from four shampoos were 98.0–100.6% (10). However, the procedure of these methods was complicated and was not suitable for routine tests. Moreover, no high-performance liquid chromatography-mass spectrometry/mass spec- trometry (HPLC-MS/MS) method for ZPT in shampoos has been reported yet. Since the formulations of shampoo were complex, HPLC method might lead to inaccurate results because of matrix interferences. In this article, both HPLC and HPLC-MS/MS methods for ZPT in shampoos were described, the HPLC was used for routine tests, and the HPLC- MS/MS was used for complex matrix samples. The sensitivity and selectivity of the devel- oped methods were appropriate for the desired application, and the methods have been used for evaluating lots of different sources of shampoos. EXPERIMENTAL INSTRUMENTATION AND REAGENTS HPLC method was carried out using a Waters 2695 system with DAD detector (Waters, Milford, MA). HPLC-APCI-MS/MS method was carried out using a Thermo TSQ Quan- tum Access system with an atmospheric pressure chemical ionization source (Thermo Scientifi c, West Palm Beach, FL). Reagent water used throughout this study was obtained from a Millipore Milli-Q water purifi cation system (Millipore, Bedford, MA). ZPT (95%) was received from Sigma- Aldrich (Steinheim, Germany). HPLC grade solvents (methanol and acetonitrile) were purchased from Merck (Darmstadt, Germany). Other reagents (ammonium acetate, po- tassium dihydrogen phosphate, EDTA-Na2, and phosphoric acid) were purchased from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). Samples were obtained from a local market.