DETERMINATION OF 13 COMPONENTS IN OXIDATIVE HAIR DYES 327 the range of 8.6–11.8 and 11.0–13.0, respectively (19). Therefore, the chromatographic resolution will be greatly infl uenced by adjusting the pH value of mobile phase. The ef- fects of four mobile phase systems at different pH values, including water–acetonitrile, citric acid buffer–acetonitrile system (pH values were adjusted to 2.6, 3.0, and 3.5), so- dium acetate buffer–acetonitrile system (pH values were adjusted to 4.0, 4.5, 5.0, and 5.5), and NaH2PO4-Na2HPO4 buffer–acetonitrile system (pH values were adjusted to 6.0, 6.5, 7.0, 7.5, and 8.0), on the separation effi ciency were investigated. Unsatisfactory separation with poor peak shape and severe peak overlapping were observed by using pure Figure 4. Online UV absorption spectra of dye intermediates. (a) Hydroquinone (b) resorcinol (c) p-aminophenol (d) phenol (e) m-aminophenol (f) 4-methylaminophenol (g) o-phenylenediamine (h) p-phenylenediamine (i) 2,5-diaminotoluene (j) 1,5-naphthalenediol (k) 3,4-diaminetoluene (l) N,N-diethyl-p-phenylenediamine (m) 2,6-diaminopyridine.

JOURNAL OF COSMETIC SCIENCE 328 Table II Recovery and Reproducibility of the Analysis of Commercial Permanent Hair Dyes by HPLC (n = 6) Compound Added (mg/kg) Hair dye Aa Hair dye Bb Found (mg/kg) Recovery (%) C.V. (%) Found (mg/kg) Recovery (%) C.V. (%) Hydroquinone 25 20.4 81.7 0.74 20.6 82.5 1.04 50 41.5 83.1 0.83 42.8 85.4 3.01 250 211.5 84.6 1.02 218.0 87.2 1.45 2500 2095 83.8 1.47 2128 85.1 1.52 Resorcinol 25 – – – 21.2 84.8 1.51 50 – – – 45.0 90.2 3.18 250 807.5 97.8 2.15 222.8 89.1 1.39 2500 3000 97.6 2.05 2318 92.7 1.12 o-Phenylenediamine 25 20.9 83.5 1.44 21.1 84.3 1.50 50 43.8 87.6 0.94 44.0 88.0 3.69 250 248.0 99.2 2.78 215.8 86.3 1.89 2500 2470 98.8 2.60 2365 94.6 1.66 1,5-Naphthalenediol 25 20.7 82.6 1.18 20.8 83.2 1.02 50 42.8 85.6 1.45 43.3 86.3 3.61 250 217.0 86.8 0.89 219.0 87.6 1.68 2500 2158 86.3 1.09 2188 87.5 1.87 2,6-Diaminopyridine 25 20.8 83.0 1.04 21.0 83.8 1.88 50 43.8 87.7 1.85 44.5 88.8 3.51 250 230.8 92.3 1.02 218.8 87.5 1.43 2500 2495 99.8 1.65 2515 100.6 1.27 p-Aminophenol 125 106.5 85.3 2.48 – – – 250 217.3 86.9 1.53 – – – 1250 1168 93.3 2.41 – – – 2500 2315 92.6 1.23 – – – Phenol 125 118.0 94.4 2.56 121.3 97.0 1.54 250 246.5 98.6 1.89 235.3 94.1 1.82 1250 1213 97.0 1.88 1193 95.4 2.35 2500 2430 97.2 1.58 2423 96.9 1.57 m-Aminophenol 125 106.3 85.0 1.92 – – – 250 212.5 85.0 1.14 – – – 1250 1178 94.1 1.83 – – – 2500 2463 98.5 3.33 – – – 4-Methylaminophenol 125 108.3 86.6 3.09 107.5 85.9 3.09 250 217.3 86.9 1.10 215.0 86.0 0.96 1250 1093 87.3 2.43 1103 88.1 2.83 2500 2158 86.3 1.84 2180 87.2 1.53 p-Phenylenediamine 125 107.8 86.3 3.05 – – – 250 220.3 88.1 2.15 – – – 1250 1175 93.9 1.90 – – – 2500 2520 100.8 1.80 – – – (Continued)