Determination of Zinc Pyrithione in Hair Care Products by Normal Phase Liquid Chromatography

A liquid chromatographic method is described for the determination of zinc pyrithione (ZPT) in shampoos, hair conditioners and hair dressings. The method involves simultaneous transchelation to the cupric complex and extraction into methylene chloride. The cupric complex is then separated by normal phase liquid chromatography and detected by UV absorbance at 254 nm. A slight modification of the chromatographic conditions allows the separation of several common impurities. When compared to alternative techniques, this procedure offers improved specificity, precision and accuracy for ZPT, as well as decreased analysis time for multiple samples.