264 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table IV Resolution of p-Phenylenediamine and Resorcinol Oxidation Products on Silica Gel and Alumina TLC Plates a Alumina plate b $1ica gel plate b distance removed, distance removed, Band color cm. c Band color cm. d Brown 0 Brown 0 Green 1.2 Blue 1.5 Yellow 1.9 Pink 4.0 Blue 3.0 Green 5.0 Yellow 4.5 Yellow 6.0 Pink 5.4 Orange Yellow 8.5 Red 6.7 Yellow 9.5 Yellow 7.1 a Solvent system, Chloroform: Ethylacetate: Methanol (6: 2: 2) b In the case of alumina plate the solvent front moved 17.0 cm, while in silica gel it moved 17.5 cm. c Resull of three development d Result of single development Adsorbent: In order to find out which adsorbent would best resolve the complicated mixtures, a number of different adsorbents with plastic or glass backing were tried as is shown in Table III. In all analyses, commercially available thin-plates were used. For these studies, silica gel plates were the most useful in • overall separation, up to 8 components were easily resolved in a single elution. Plates with a flexible inert phase, such as plastics or glass fiber web, never equaled the quality of resolution obtained on glass plates--even when identical adsorbent phases were used. Although Chroam AR sheets* carried the same *Mallinckrodt Inc., St. Louis, MO.

THIN-LAYER CHROMATOGRAPHY Table V 265 Solvent Selection Dye Group Properties Solvent 1 Fast moving, low molecular wt. Ether: chloroform one or two ring structures 2 Two or three ring structures Chloroform: ethylacetate: methanol Chloroform: DMF Alcohol, DMF, DMSO 3 Immobile polymeric solid phase as the thin-layer plates, they did not have the sharpness of the resolution of the analytical plates. All of the components diffused much more, not only in the direc- tion of the elution, but also perpendicular to it as well, showing channeling of the solvents along the fibers which form an isotroric web. This resulted in more extensive component spreading. Alumina was less efficient in performing the total analysis of all product-compositions studies. In some instances, alumina gave much sharper or cleaner separations for specific components. Specificity was not a characteristic of pH, but of the adsorbent it- self, and it was qualitative for most components in the form of no adsorption or extremely strong adsorption. Development time was slightly reduced when a glass adsorbent was used, but there was poor resolution, especially for the fast-moving and slow-moving components. Good resolution was never achieved with cellulose solid phase either in the form of papers or TLC plate. Table IV shows the resolution of PDA and resorcinol oxidation products on silica gel and alumina plates. On silica gel plates, the product is well resolved and there is not much specificity of strongly adsorbed and nonadsorbed components. On alumina plates, the fast-moving pink and many other components stayed close to the origin. So/vent: A difficult task in this study was the choice of a proper solvent or solvents, as no one system was found which resolved all components simultaneously. From the point of view of solvent requirement, all dye components can be divided into 3 groups (Table V). The dyes belonging to Group 1 are low molecular weight, one-ring or two-ring struc- tures (such as nitro aniline) and are compounds which are mostly orange, yellow, or red. These components are usually water soluble. This group of dyes can be separated by using chloroform and ether in different ratios. The dyes in Group 2 include all the specific dye components, which are of primary im- portance for the shade and intensity of hair color. They are components containing 2 or 3 rings bound by nitrogen or oxygen. The elution system for the resolution of these components must contain significant amounts of highly polar and hydrophilic components such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), and al- cohols, as well as low-activity solvents, such as halogenated hydrocarbons. In an arbitrary way, all dye components, which did not elute with the above solvent systems, were grouped as polymeric materials (Group 3). They are mostly immobile and can be resolved partially using DMF, DMSO, or methanol.