DETERMINATION OF ZPT IN SHAMPOOS BY HPLC AND HPLC-MS/MS 271 was optimized in MRM mode to get the best sensitivity. The optimum settings were found to be: discharge current: 4 μA, vaporizer temperature: 400°C, sheath gas pressure: 40 psi, aux gas pressure: 5 psi, capillary temperature: 300°C. Under optimized conditions, the resultant APCI-MS-MS spectrum for ZPT depicted three signifi cant ions, the quasi- molecular (M + H)+ ion at m/z 317.0 and other two ions at m/z 173.8 and 189.8. Figure 3. TIC (total ion chromatography) of ZPT in normal C18 (A) and Chromolith Performance RP-18e column (B). Figure 4. Chromatography of blank shampoo sample with 0.05% ZPT.

JOURNAL OF COSMETIC SCIENCE 272 METHOD PERFORMANCE OF HPLC Linearity was determined in the region of 3.2–200.0 μg·ml−1, and the calculated re- gression coeffi cient was R2 = 0.9989. The limits of detection and quantization were calculated as three and ten times the standard deviation of the baseline noise for blank extractions of shampoo, respectively. The limits of detection and quantization were 0.015% and 0.05%, respectively. Although the detection limit of HPLC method was not low, it was enough for routine analysis of cosmetics, which was above 0.1% in most cases. Precision and repeatability was evaluated at three levels (blank shampoo sample with 0.1%, 0.5%, and 2% ZPT). The relative standard deviation (RSD) of six injections was Figure 5. Chromatography of blank shampoo sample with 0.01% ZPT. XIC (extracted ion chromatogra- phy at m/z 173.8).