JOURNAL OF COSMETIC SCIENCE 326 Figure 4. Continued

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.