FOURIER TRANSFORM INFRARED SPECTROSCOPY OF HAIR 65 1.60 I { B •. o- Wavenumbers [cm ] Figure 2. Diamond cell spectra of virgin (A) and bleached (B) hair. 1042 cm-1 has been assigned to a symmetric S = O stretching vibration of sulfonate or sulfonic acid groups of cysteic acid residues, and its absorbance, therefore, is a measure of the - SO j content of hair (10). Spectral subtraction makes for easy elucidation of the spectra of oxidized or reacted species. A virgin hair spectrum was subtracted from both a bleached and a bisulfite- treated hair spectrum. The resulting difference spectra are shown in Figures 3 and 4.

66 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 0.12. 0 Wavenumbers Figure 3. Difference spectrum of bleached hair minus virgin hair. Except for some frequency differences, the spectrum in Figure 3 is comparable to the one previously reported (5) for six-times-bleached hair. Previous band assignments (1- 3,5) placed the symmetric and asymmetric sulfonate S=O stretching vibrations at 1040 cm-• and 1175 cm-•, while we found these vibrations at 1042 cm-• and 1188 cm-•. The bands at 1219 cm-• and above can be assigned to the cysteic acid moiety. All are seen in L-cysteic acid (12), including a band near 740 cm -• The Bunte salt groups (- S- SO •) in Figure 4 are readily distinguished from the cysteic acid residues of bleached hair. The bands found at 1196, 1022, 633, and 525 cm-• are assigned to thiosulfate groups. Previous researchers (13) reported bands near 1190, 1022, 630, and 520 cm-• for methyl and ethylthiosulfate ions, which they assigned to the S = O asymmetric stretch, S = O symmetric stretch, S = O symmetric deforma- tion, and the S = O asymmetric deformation vibrations of the thiosulfate ions, respec- tively. Again, the bands at 1231 cm-• and above can be assigned to the cysteine moiety attached to the thiosulfate group. REPRODUCIBILITY OF THE METHOD Ratios were taken of the 1042 cm-• oxidation band (S = O) intensities against peptide (hair) bands before and after subtracting virgin hair spectra. The peptide bands used