HAIR ANALYSIS BY ToF-SIMS 277 Repeated application of the alkylamidopropyl ethyl dimonium ethosulfate conditioner, I 18-MEA 40, to hair, under applications identical to those of the Incroquat Behenyl 18-MEA treatments, produced an obvious change in the positive-ion ToF SIMS spec­ trum, with strong ion intensity observed at m/z = 439 + due to adsorption of the 18-MEA C 21 derivative (Figure 11). To further confirm this substantivity, the Incroquat 18-MEA 40 was similarly applied to "clean" wool and "clean" bleached wool, where similar strong spectral profiles were observed, indicating unequivocal evidence for the Incroquat 18-MEA and, in particular, the C 21 derivative adsorption. Finally, "clean" wool was treated with the commercial Incroquat Behenyl 18-MEA formulation, with the ion intensities at m/z = 340+ and 368+, respectively, dominating the positive-ion ToF-SIMS spectrum. However, in addition, examination of the higher mass range also indicated the presence of the characteristic ion intensity series at m/z = 411 + , 42 5 + , and 439 + , respectively, which can be assigned to the I 18-MEA 40 softener component (Figure 12). CONCLUSIONS The surface-sensitive ToF-SIMS analytical technique has been successfully used to probe the surface of human hair. Silicones, anionic surfactants, and cationic softeners can be clearly detected on the surface of the commercial "as received" human hair. Cleaning of the hair with anionic surfactant solutions, SDS and SLES, results in a relative increase in the ToF-SIMS spectral intensity of the larger alkyl chains (more non-polar components 3500-t---....___.......,____.____,_____.___._____..,______.____,___-+ 3000 2500 2000 !! C ::I 0 o 1500 1000 500 □ + 0 * hJ J \J t tJ�)U� J JJ_J_i 0-+==--;;:;;;;c--____;,;,,--,,---.----....-------.----r------ir----.--..=.;..,-r-�;;.;.._---+ 300 320 340 360 380 400 m/z 420 440 460 480 500 Figure 11. Positive-ion ToF-SIMS spectrum of cleaned, unbleached hair treated with 2% I 18-MEA 40 solution. Treatment was repeated three times, with rinsing of the treated hair in water after each treatment. *, C22 derivative. +, C21 derivative. D, C20 derivative. o, C 19 derivative.

278 JOURNAL OF COSMETIC SCIENCE 25+------'-----'-----'----_,_--_,_----'----....L------'--------''----+- 20 □ 0 15 10 5 420 + 440 460 480 500 m/z 520 540 560 580 600 Figure 12. Positive-ion ToF-SIMS spectrum of "clean," bleached wool treated with 2% IB 18-MEA solution. Treatment was repeated three times, with rinsing of the treated wool in water after each treatment. *, C22 derivative. +, C21 derivative. D, C20 derivative. O, C1 9 derivative. of the surfactant solution at the hair surface) suggesting their greater substantivity to the hair. Cleaning of the hair in these -so-ltttions does not remove all the silicones or cationic surfactant residues from previous treatments. Aqueous hydrogen peroxide bleaching of human hair resulted in a decrease in the ToF-SIMS spectral intensity of the 18-MEA bound to the hair surface protein via thioester linkage. Application of the 18-MEA-enriched cationic conditioner formula­ tion, Incroquat Behenyl 18-MEA, to unbleached and bleached hair resulted in adsorp­ tion of predominantly the C 18 , C 20 , C 22 softener derivatives onto the hair surface. The ToF-SIMS data indicates that the level of adsorption of the cationic conditioner is greater on the negatively charged, bleached hair fiber surface than on the undamaged virgin hair. Intermediate rinsing in SLES, in comparison to water rinsing alone, appears to reduce the concentration of conditioner at the hair fiber surface. The alkylamidopropyl ethyl dimonium ethosulfate, I 18-MEA 40, derived from 18-MEA, is a smaller com­ ponent of the commercial Incroquat Behenyl 18-MEA conditioner. Nevertheless, its adsorption/substantivity to hair and related keratin fibers, wool, has been demonstrated even though competitive adsorption is occurring during the IB application. ACKNOWLEDGMENTS The authors acknowledge Dr. Tim Gao, Dr. Rob Comber, and Dr. Surinder Chahal for their technical expertise with this paper, as well as Croda Pk for for its financial support.