DETERMINATION OF ZPT IN SHAMPOOS BY HPLC AND HPLC-MS/MS 273 evaluated and analyzed with different analysts and different apparatus. Precision tests demonstrated that the method yielded good precision (RSD 4.53%). Reproducible injections were also satisfactory with RSD values ranging from 0.33% to 5.12%. (Figure 4). The recovery experiments were performed in triplicate. The recovery data were deter- mined by dividing the value obtained for the sample prepared with the added standard, by the amount added, and then multiplying by 100%. The percentage recoveries were found to be 85.8–104% (Table V), which were satisfactory in all cases. Therefore, quan- tifi cation by external calibration can be effectively employed. METHOD PERFORMANCE OF HPLC-MS/MS Linearity was determined in the region of 1.0–200.0 μg·ml−1, and the calculated regres- sion coeffi cient was R2 = 0.9991. The limits of detection and quantization were 0.003% and 0.01%, respectively. Table V Recovery Tests Sample Method ZPT added in the sample (%) Analysis results (%) Recovery (%) CV (%) 1 HPLC 0.05 0.0436 87.2 2.36 0.35 0.312 89.1 3.56 1.06 0.909 85.8 2.13 1.76 1.65 93.7 1.99 HPLC-MS/MS 0.05 0.0438 87.6 4.21 0.35 0.325 92.9 2.96 1.06 0.996 94.0 3.12 1.76 1.72 97.7 2.01 2 HPLC 0.010 — — — 0.064 0.0589 92.0 3.68 0.16 0.155 96.9 4.21 1.60 1.67 104 2.89 HPLC-MS/MS 0.010 0.00926 92.6 4.57 0.064 0.0605 94.3 2.16 0.16 0.171 107 1.57 1.60 1.65 103 3.00 3 HPLC 0.05 0.0463 92.6% 2.68 0.35 0.321 91.7% 2.01 1.06 0.909 85.8% 3.66 1.76 1.56 88.6% 1.95 HPLC-MS/MS 0.05 0.0483 96.6% 3.21 0.35 0.352 101% 1.96 1.06 0.969 91.4% 2.13 1.76 1.78 101% 3.26

JOURNAL OF COSMETIC SCIENCE 274 Sample Method ZPT added in the sample (%) Analysis results (%) Recovery (%) CV (%) 4 HPLC 0.010 — — — 0.064 0.0590 92.2% 2.63 0.16 0.165 103% 3.21 1.60 1.60 100% 3.01 HPLC-MS/MS 0.010 0.00946 94.6% 4.26 0.064 0.0600 93.8% 1.29 0.16 0.161 101% 1.86 1.60 1.68 105% 2.67 5 HPLC 0.05 0.0446 89.2% 3.25 0.35 0.322 92.0% 1.98 1.06 0.999 94.2% 2.56 1.76 1.67 94.9% 2.74 HPLC-MS/MS 0.05 0.0478 95.6% 3.65 0.35 0.315 90.0% 2.96 1.06 0.986 93.0% 2.68 1.76 1.75 99.4% 1.98 6 HPLC 0.010 — — — 0.064 0.0598 93.4% 4.26 0.16 0.159 99.4% 2.36 1.60 1.60 100 % 1.98 HPLC-MS/MS 0.010 0.00962 96.2% 3.58 0.064 0.0650 102% 2.96 0.16 0.170 106% 1.65 1.60 1.56 97.5% 1.33 7 HPLC 0.05 0.0430 86.0% 4.36 0.35 0.310 88.6% 2.86 1.06 0.990 93.4% 2.98 1.76 1.69 96.0% 2.01 HPLC-MS/MS 0.05 0.0448 89.6% 4.99 0.35 0.345 98.6% 1.58 1.06 1.09 103% 2.38 1.76 1.70 96.6% 3.00 Table V Continued Precision and repeatability was evaluated at three levels (blank shampoo sample with 0.02%, 0.1%, and 1% ZPT). The RSD of six injections was evaluated and analyzed with different analysts and different apparatus. Precision tests demonstrated that the method yielded good precision (RSD 4.9%). Reproducible injections were also satisfactory with RSD values ranging from 4.2% to 6.8%. The recovery experiments were performed in triplicate. The percentage recoveries were found to be 87.6–107% (Table V), which were satisfactory in all cases. Therefore, quan- tifi cation by external calibration can be effectively employed. (Figure 5).