DETERMINATION OF ZPT IN SHAMPOOS BY HPLC AND HPLC-MS/MS 275 SAMPLE TESTS The established HPLC and HPLC-MS/MS methods were used to test several same sham- poos to investigate the consistency. Through t-test, these two methods showed no statisti- cal difference (p 0.05). Research analyzed 102 batches of shampoos in China, especially antidandruff shampoo. Among all, 44 antidandruff samples contained ZPT ranged from 0.11% to 1.46% (all of them below the Chinese regulation). Most brands of antidandruff shampoo (52.6%) con- tained ZPT as the active ingredient. CONCLUSION The simple sample preparation procedure coupled with HPLC and HPLC-MS/MS detec- tion was developed for the analysis of ZPT in shampoos. The pretreatment step (used water to wash the sample) could effectively remove water-soluble surfactants and impuri- ties that might pollute the chromatography and mass spectrometry system. To our knowledge, no similar pretreatment step has been reported in other published methods. And other common antidandruff agents (salicylic acid, ketoconazole, climbazole, and piroctone olamine) also could be analyzed in the same chromatography condition. These methods were validated in a real sample matrix and showed high sensitivity with acceptable recovery and reproducibility, while also yielding a limit of detection that was adequate for the detection of real samples. 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). The reproducibilities were 0.33–5.12% (HPLC) and 4.2–6.8% (HPLC-MS/MS). The HPLC method was suitable for high-throughput routine analysis, and the HPLC-MS/MS was suitable for complex matrix samples. REFERENCES (1) J. D. Nelson and G. A. Hyde, Sodium and zinc omadine antimicrobials as cosmetic preservatives, Cos- met. Toilet., 96, 87–90 (1981). (2) A. Babar, C. Kawilarang, A. J. Cutie, and F. M. Plakogiannis, In-vitro release of zinc pyrithione from a shampoo base and the effects of various additives on its release rate, Drug Dev. Ind. Pharm., 11, 1507– 1522 (1985). (3) A. R. Jeffcoat, W. B. Gibson, P. A. Rodriguez, T. S. Turan, P. F. Hughes, and M. E. Twine, Zinc pyridi- nethione: urinary metabolites of zinc pyridinethione in rabbits, rats, monkeys, and dogs after oral dos- ing, Toxicol. Appl. Pharm., 56, 141–154 (1980). (4) I. K. Genji and O. M. Kikuhiko, The effect of zinc pyrithione on human skin cells in vitro, J. Soc. Cosmet. Chem., 34, 1–11 (1983). (5). A. B. G. Lausdown, Interspecies variations in response to topical application of selected zinc, Food Chem. Toxicol., 29, 57–64 (1991). (6) T. Okumura, J. Koyama, Y. Ohtsu, K. Nakamura, O. Nakata, and N. Tanaka, Proc. 9th Conf. on Liquid Chro- matography, Division of Liquid Chromatography of the Japan Society for Analytical Chemistry, Tokyo, 137, (1988). (7) J. Bones, K. V. Thomas, and B. Paull, Improved method for the determination of zinc pyrithione in environmental water samples incorporating on-line extraction and preconcentration coupled with liq- uid chromatography atmospheric pressure chemical ionisation mass spectrometry, J. Chromatogr. A, 1132, 157–164 (2006).

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