OXIDATIVE HAIR DYES 111

112 JOURNAL OF COSMETIC SCIENCE i , 20 25 30 a • m-am•phenol ß toluene-2,5-diamine ß 2,4- diaminophenoxyethanol t• resorcinol 35 40 45 50 55 60 65 Column temperature (øC) 30.0 30.0 b •_, 22.5- '• 15.0- g 7 7.5 -3.0 0.0 2.0 4.0 6.0 9.0 22.5 - 15.0 - 7.5- -3.0 0.0 5-6 M 7 I I I 2.0 4.0 6.0 8.0 Retention time (min) Figure 2. Influence of temperature on the separation of a mixture of hair dyes. a: standard mixture of toluene-2,5-diamine sulfate and 2,4-diaminophenoxyethanol at the same concentration. b: separation at 60øC of the same standard mixture. c: separation of a dark blonde shade commercial shampoo at the optimum temperature of 60øC. Peaks: see Figure 1. 2b), while they cannot be discriminated using that unique type of detection in the dark blonde shade shampoo (DBLS), for example, because of their large concentration ratio even at the optimum temperature of 60øC (Figure 2c). On-line mass spectrometry detection (associated with the photodiode array for compari- son purposes) was then used for the identification. An example is shown (Figure 3) for the identification of the two hair dyes cited above in the dark brown shade shampoo (DBRS). The major noticeable point is the absence of interference between the com- pounds, allowing a precise identification based on the specific transitions existing be- tween the parent and daughter ions for each selected compound. In the example shown,