82 JOURNAL OF COSMETIC SCIENCE . c c 0- -1 180 160-' 140- o 120: -o 100-' - 40: a' Edge of the polymer n3JItilayer k=31•rn = -_ : • - -- 6 ,• 1'0 1'5 Distance (rricrons) B' Edge of the hair •.= 31.• •) 1'0 1'5 Distance (rricrons) Figure 7. Absorbance profiles of the 3-micron wavelength of the edges of the polymer multilayer (A) and the edge of the hair (cuticle) (B). Recording conditions are the same as in Figure 5B. samples, all of which exhibit similar results. Note that the lateral resolution obtained using 3-micron wavelength light is confirmed with the profile shown in Figure 7A and is -4 microns. CHEMICAL IMAaINa OF •LEACHED HAm Infrared spectroscopy has been used by a number of investigators (2,4,11) to study

CHEMICAL IMAGING OF HAIR BY IMS 83 1.5 1.0 0.5 0.0 1 ! , : ? I :I : I : ! ! ............ Co flex -- Cuticle i -0.5 1800 1700 1600 1500 1400 Frequency (cm -1) Figure 8. Infrared spectra between 1850 cm • and 900 cm • of cuticle and cortex of the untreated hair. Spectra were recorded with 3-pm x 3-pm apertures, at 4 cm -• resolution, and 128 scans were co-added. keratin oxidation. Hydrogen peroxide used for bleaching leads to oxidative cleavage of disulfide bonds and finally to the formation of cisteic acid. The effect of bleaching and weathering on hair can be studied by looking at the symmetric and asymmetric sul- phonate S--O stretching vibrations at 1040 cm • and 1188 cm -• (2). The band at 1219 -1 ß 1 -1 cm lS assigned to cysteic acid moiety the bands at 1196 cm and 1022 cm are assigned to the assymetric and symmetric S--O stretch vibrations of thiosulphate ions (Bunte salt) (2) (Table I). Other characteristic bands are available below 900 cm i but were not studied here because of increased diffraction effects and the refractive index variation of the BaF 2 substrate (22). Figure 9 shows the spectra obtained between 1850 -1 cm and 900 cm • before and after bleaching. The typical sulphonate stretching vibration band at 1040 cm -1 is shown. At higher frequencies, the other vibrations all overlap to form a large band between 1138 cm -1 and 1286 cm -• Although bleaching is a well-known chemical process, the spatial distribution of the induced chemical changes have never been studied. For this purpose, we use the sym- metrical sulphonate vibration, where the band intensity is directly related to the cysteic acid content of the hair (4). Figure 10B shows the contour map obtained from the integrated absorbance of the symmetric stretching vibrations S=O (1040 cm -1) as a function of position. The mapping was acquired through a square area of 11 pm x 11 pm in 6-pm steps, and 64 scans were co-added for each spectrum. The sulphonate signature is present everywhere within the hair. We noticed a heterogeneous distribution of the sulphonate band through the cortex in this region, and the contribution of the sulphonate is between 20% and 30% higher than elsewhere in the hair. The sulphonate lateral distribution can be compared with the distribution of the amide A band shown