238 JOURNAL OF COSMETIC SCIENCE Butylated Hydroxytoluene 1000-- 500• -s22| I 200 300 Figure 1. UV spectra of three matrix products. 400 Wavelength (nm) Sample solutions containing an additional matrix compound and three dye intermediates. From the forty-seven dye intermediates tested, four were chosen for further investigation based on how representative they were of their different classes of hair dyes as well as on their use in formulations. Three sample solutions were prepared, each containing a mixture of three selected dye intermediates (1,4-pd or 4-ap, res, and 2-n-l,4-pd), the intrinsic matrix compound NaAsc as an antioxidant, and another major matrix compound, BHT, DMDM, or EOP, respectively. BHT is an important antioxidant, DMDM a commonly used preservative, and EOP a perfume solubilizer. The retention time of BHT and EOP is more than 30 min, while DMDM is eluted within about 7 min. Three control solutions, mixtures of the respective dyes without the major matrix compound, were also prepared. All the components were at the concentrations used in formulations according to COLIPA, and five injections of each type of solution were made. For each series of measurements of control and mixture, a new column was used, as it has been shown in a preliminary study that after 50 injections, the efficiency of the column is dramatically decreased (data not reported). Table IV gives the statistical results obtained for the retention times and the corrected peak areas for each of these compounds. Comparison of the data between mixture ! (BHT) and control 1, mixture 2 (DMDM) and control 2, and finally mixture 3 (EOP) and control 3 leads to several observations. First of all, as shown by the results, DMDM or EOP do not interfere with the dye intermediates or with the column in a way that would change the chromatographic

MATRIX COMPOUNDS AND OXIDATIVE HAIR DYES 239 Table IV Retention Times and Corrected Peak Areas for Three Matrix Compounds and Four Dye Intermediates in D•,e-Matrix Mixtures and in Control Solutions (n = 5) Retention time (min) Corrected peak area (AU) Column Mixture Compound Mean RSD (%) Mean RSD (%) 4-ap 5.59 0.85 11.5 7.2 res 9.31 1.14 0.3 3.1 1 2-n-l,4-pd 13.75 0.53 9.1 21 NaAsc 2.18 0.38 54.7 7.8 1 BHT 38.07 • 0.55 2.5 19.0 4-ap 5.57 0.40 10.6 5.9 res 9.55 0.82 0.3 5.0 Control 1 2-n-l,4-pd 13.89 0.50 10.0 6.5 NaAsc 2.18 0.21 56.5 8.0 1,4-pd 5.36 0.39 14.6 1.6 res 8.32 0.34 0.5 2.9 2 2-n-l,4-pd 12.91 0.55 14.4 1.1 NaAsc 2.35 0.60 70.3 2.3 2 DMDM 6.72 0.42 5.4 15.1 .......... 1,4-pd 5.33 0.19 15.0 2.0 res 8.28 0.53 0.5 1.3 Control 2 2-n-l,4-pd 13.28 3.39 14.4 3.8 NaAsc 2.35 0 80.7 1.5 4-ap 5.99 0.39 22.1 1.7 res 9.53 0.79 0.6 1.5 3 2-n-l,4-pd 14.09 0.39 20.4 1.6 NaAsc 2.27 0.25 35.7 5.5 3 EOP 36.05 0.71 6.4 0.6 4-ap 6.32 0.88 22.7 2.0 res 10.26 1.99 0.6 5.9 Control 3 2-n-l,4-pd 14.84 1.42 20.3 1.6 NaAsc 2.24 0.24 53.2 6.3 behavior (retention time, corrected peak area) of the dye intermediates. Furthermore, they do not alter the repeatability of the separation. For instance, when DMDM is added to the sample, the RSD on the retention time of the various hair dyes varies from 0.3%