STAINING CATIONICS ON KERATIN 207 (TEALS), rubbing by hand for two minutes, and then rinsing under 100 degrees F running tap water for an additional two minutes. Following overnight drying, the washed swatches were cut with a pair ofpinking shears into 0.14-g segments, having areas of approximately 1.3 square inches, and put aside for use in binding experiments. In general, five swatches were prepared for each treat- ment. In all binding experiments, stainless steel wire gauzes with rectangular holes cut slightly smaller than the test swatches were placed over beakers. A test swatch was then wet with tap water, excess water squeezed out, and the swatch placed over the hole. Then, 0.3 ml of test solution was applied as evenly as possible to the wool, which was rubbed for one minute between two lengths of rubber tubing mounted on metal rollers. The wool swatches were rinsed in a beaker of tap water for 45 seconds, followed by a 15-second rinse in a second beaker, after which very little radioactive material could be removed from the wool by further rinsing. A final rinse was performed for one minute under running tap water. Depending upon the particular experiment, after the above-mentioned treatment, wool swatches could be either hung up to dry or treated again after squeezing out excess water using rubber tubing placed over the ends of crucible tongs. After drying, wool swatches were dissolved by placing each in a counting vial, adding 1 ml of 2M NaOH, and heating in an oven for 1.5 hours. Three reference vials were also prepared, in which a wool swatch was dissolved following addition of a known amount of the radiolabeled compound being tested. After cooling, approximately 12 ml of Aquasol-2 LSC cocktail was added to each vial, followed by addition of 0.25 ml of concentrated perchloric acid. The vials were then shaken vigorously, resulting in a clear solution ready for counting. RESULTS AND DISCUSSION For initial testing, CTAC and SAC, two commonly used conditioning actives, were selected for study. In one of the first experiments, a series of alkyl sulfates of varying chain length (C8, C10, C12, C14) was selected to simulate the shampooing detergent. These alkyl sulfates were used to wash swatches treated with CTAC and then stained according to the procedure described in the experimental section. The results of this experiment are depicted in Figure 1, which shows less staining for the swatches washed with C8 and C 10 alkyl sulfates compared to the swatch not washed with anionic detergent, and no staining for the swatches washed with C12 and C14 alkyl sulfates. Similar results were obtained for both bleached and light blonde hair tresses, with less overall staining for the unbleached hair. The initial, but erroneous, conclusion was that dodecyl and tetradecyl sulfates are more effective for removing CTAC from the keratin. The next step was to run a quantitative adsorption experiment to help explain these dye-staining results. In this study we actually compared the removal of labeled SAC from swatches by labeled SDES and ALS. Swatches treated with SAC or CTAC stain similarly after washing with anionic detergents such as SDES and ALS, i.e., washing
208 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS CTAC CTAC/C-$ CTAC/C-10 [ CTAC/C-12 CTAC/C-14 ALKYL SULFATES Figure 1. Wool swatches stained with Red-80 dye after treatment with CTAC and washing with alkyl sulfate detergents. SAC-treated swatches with either SLS or ALS leaves no stain, while washing with SDES leaves a light orange-red stain (see Figure 2). The results of this tracer experiment are summarized in Table I. In view of the dye- staining results of Figure 2, the radiotracer results were surprising. Surprisingly, the radiotracer experiment shows more SAC on the lauryl sulfate-washed swatch that did not stain with Red-80 than on the swatch washed with SDES that picked up stain. In addition, the ratio of anion to cation is roughly 1. Apparently, the stearalkonium cation interacts with the washing anion and the resul- tant complex is either washed into the aqueous phase or it deposits on the keratin. When lauryl sulfate is the washing anion, the complex binds so firmly that on subse- quent staining with the anionic Red-80 dye, the stearalkonium ion is not free to in- teract with the anionic dye and therefore staining does not occur. This lack of staining occurs in spite of the large amount of stearalkonium species left on the keratin. Not only is there less cationic bound to the swatch after washing with SDES vs. ALS, but some of the anionic dye can displace the deceth sulfate and bind to the stearalkonium cation and thereby stain the SDES-washed swatch. In this new modified staining procedure, if the swatch stains, not only is cationic present, but the anionic detergent is either not bound to the cationic conditioner or it does not bind firmly enough to the cation to prevent staining on subsequent treatment with anionic dye. If staining does not occur, then either no cationic conditioner is present, or the deposited cation binds so firmly to the washing anionic detergent that the anionic dye cannot displace the anionic species and staining cannot occur. In our experience, when staining does not occur, this latter condition is the usual situation for most commonly used cationic conditioning agents (6).
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