HAIR ANALYSIS BY ToF-SIMS 267 minutes, at 20°C and with a hair:liquor ratio of 1 :25. The hair was gently agitated in the bleach bath. After bleaching, the hair was rinsed in excess water and air dried. INCROQUAT BEHENYL 18-MEA (IB 18-MEA) The SLES-cleaned hair and bleached hair were treated with a 2% IB 18-MEA solution at 30°C for five minutes at a hair:liquor ratio of 1:50. The hair samples were then rinsed in water and air dried. This procedure was repeated twice and the samples were finally air dried. Another set of IB 18-MEA samples was prepared as above but with additional pre-cleaning in a 2% SLES solution, over five minutes, followed by rinsing in excess water prior to the IB 18-MEA treatments. ALKYLAMIDOPROPYL ETHYL DIMONIUM ETHOSULFATE (I 18-MEA 40) The related I 18-MEA 40, derived from 18-MEA, treated samples were similarly pre­ pared as described for the IB-18-MEA samples. ToF-SIMS ANALYSIS The ToF-SIMS spectra were obtained under static conditions using a PHI 7000 instru­ ment with a reflectron analyzer, a Cs+ ion source (8 KeV, pulse length 50 ns), and a pulsed electron flood source (50-70 eV) for charge compensation. The operating pressure was less than 5.33 µPa (4 x 10-s torr). For each sample analysis, a total primary-ion dose of fewer than 1 x 10 12 ions cm-2 was used, which lies well below the threshold level of 1x10 13 ions cm -2 for static SIMS (10). The hair fibers were mounted by stretching them over a sample stub and then fixing them by using a standard ring-clamping arrange­ ment. Both positive and negative ion spectra were acquired from an area of 250 µm x 250 µm in the mass range of m/z = 0-1000. The data presented is based on duplicate/ triplicate measurements, with the fibers analyzed at the same position along the fiber shaft. ToF-SIMS analyses of the surfactant/conditioner films were obtained by air drying the liquid sample on clean aluminium foil and analyzing as previously described. RESULTS AND DISCUSSION ToF-SIMS analysis of the "as received" European brown hair revealed significant surface contamination (Figures 1, 2). In the positive-ion ToF-SIMS spectrum there was clearly evident a series of cationic quaternary ammonium conditioner species present with the general formula (R) 2 N+ (CH3)2 (Table I). In addition, silicone contaminants at m/z = 133 + , 14r, 2or, 221 +, and 281 + were also detected in the lower mass range. Similarly, the negative-ion ToF-SIMS spectrum indicated the presence of silicone (m/z = 223 -), with additional anionic alkyl sulphate surfactants detected at m/z = 265 -, 293 -, and 321 -, which can be assigned to the C 12 , C 14 , and C 16 derivatives, respectively (Figure 2). The presence of these additional surface species is obviously of concern since many fundamental studies may be adversely affected by these normally undetected contami­ nants. Therefore, it may be advisable that the hair be pre-cleaned and examined by ToF-SIMS prior to use. Nevertheless, in this study the negative-ion ToF-SIMS spectrum

268 JOURNAL OF COSMETIC SCIENCE 600-1----___JL_ __ ----'------'-----......_--___._------r 500 400 200 550 600 Figure 1. Positive-ion ToF-SIMS spectrum of European brown hair (as received). *, Cationic softener species. 700 600 500 § 400 300 □ 200 100 m � m m � m � � � � Figure 2. Negative-ion ToF-SIMS spectrum of European brown hair (as received). *, Lipids. +, Silicone. D, Surfactant. of the hair still indicates the characteristic lipids present at the surface of keratin fibers (Figure 2, Table II). In particular, the 18-methyl eicosanoic acid (18-MEA, m/z = 341 -) bound to the hair protein via predominantly a thioester linkage, although fatty ester bonding also occurs, is the major lipid species detected. Examination of the negative-ion ToF-SIMS spectrum of the sodium dodecyl sulphate (SDS) film indicates the major component is indeed the C 12 species at m/z = 265- (Figure 3). However, C 14 and C 1 6 alkyl sulphates were also detected by the ToF-SIMS technique, as indicated by signal intensity at m/z = 29r and 321 -, respectively. Cleaning of the hair in the SDS solution, followed by subsequent water rinsing, reduced the surface silicone signal, with the 18-MEA signal becoming more apparent (Figure 4). However, the alkyl sulphate surfactants are still clearly evident and even after rinsing with the C1 6 derivative at m/z = 321 - increased in intensity relative to the C 12 species