FOURIER TRANSFORM INFRARED SPECTROSCOPY OF HAIR 67 0.3 Wavenumbers [cm -• ] Figure 4. Difference spectrum of bisulfite-waved hair minus virgin hair. were near 1650 cm-• (amide I), 1230 cm-• (amide !II), and 1076 cm-1. The absor- bance ratios for the once-bleached tresses (Samples A) are shown in Table I. The coefficient of variation (CV) was calculated for each group of nine ratios, and the 1042 cm-• band intensities were correlated with the peptide band intensities. Both statistical evaluations showed the same result. Clearly the 1235 cm-• band was the best internal standard to use, with little to choose between the 1100 cm-• or the 900 cm-1 baseline. Lower variances (better precision) and better correlations were obtained when the 1042 cm- • band intensity was obtained after subtraction of the hair spectrum. The fact that the amide III band gave the most reliable ratio is understandable. The 1076 cm-t band was too close to, and interfered with, the sulfonate band. The amide I band was often out of the linear range of Beer's law (absorbances were usually between 1 and 1.5 a.u.). The results obtained with thioglycollate-waved (samples B) and bisulfite-waved (samples C) tresses are shown in Tables II and III. In more than half of these spectra, the S = O band at 1042 cm- • appeared as an unresolved shoulder. Peak intensities were, therefore, obtained after subtracting the virgin hair spectra. The baseline used to determine the 1042 cm-• peak height after subtraction was at a minimum near 1060 cm -•. Smaller peak intensities combined with baseline uncertainty caused the lower precision and peak height correlations for the waved hair compared to the more heavily oxidized bleached hair (Table I). The choice of the amide band that was used for the ratio calculation made little difference to the precision of the results. The degree of oxidation for the waved hair (samples B) was about one third that of the bleached hair (sam- ples A).

68 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Absorbance Ratios of the Sulfonate Oxidation Band (1042 cm-•) Against Peptide Bands for Once-Bleached Hair (Samples A) Before Subtraction After Subtraction 1042 1042 1042 1042 1042 1042 1042 Frequency (cm- •) 1076 1650 1235 1235 1650 1235 1235 (Baseline, cm -•) (--1050) (--1900) (--1100) (--900) (--1900) (--1100) (--900) Tress 1 0.727 0.011 0.058 0.041 0.023 0. 120 0.084 1.027 0.018 0.092 0.061 0.036 0. 178 0. 118 0.872 0.015 0.069 0.045 0.035 0. 163 0. 106 Tress 2 0.988 0.008 0.078 0.054 0.028 0.159 0.110 0.445 0.014 0.045 0.032 0.018 0. 102 0.072 0.838 0.015 0.071 0.050 0.029 0. 136 0.096 Tress 3 1.851 0.015 0.090 0.068 0.026 0.159 0.120 1.020 0.018 0.079 0.054 0.032 0. 143 0.098 2.634 0.030 0. 130 0.090 0.042 0. 178 0. 123 Mean 1. 156 0.016 0.079 0.055 0.030 0. 149 0.103 CV (%)* 58. ! 39.5 30.5 30.8 24.4 17.5 16.6 Corr. Coeff.** 0.15 0.37 0.62 0.63 0.60 0.82 0.85 * Coefficient of variation for 9 determinations. ** Correlation coefficient of 1042 cm-• band against peptide band intensities. Coefficients of variation were calculated from the ratios in Tables I and III to determine the precision of triplicate analyses within each tress and the variability between replicate tresses. Representative values are shown in Table IV. While considerable variability was found between fibers of the same tress, the variability between the triplicate means Table II Absorbance Ratios of the Oxidation Band (1042 cm-2) After Subtraction Against Peptide Bands for Once-Thioglycollate-Waved Hair (Samples B) 1042 1042 1042 Frequency, (cm- •) 1650 1235 1235 (Baseline, cm- •) (-- 1900) (-- 1100) (--900) Tress 1 Tress 2 O.OO79 O.O225 0.0073 O.OO67 0.0035 O.OO93 Tress 3 0.0057 0.0085 0.0129 Mean 0.0094 CV (%)* 59.4 Corr. Coeff.** 0. 569 0.045 0.032 0.126 0.081 0.039 0.024 0.033 0.024 0.021 0.013 0.055 0.039 0.026 0.018 0.053 0.036 0.069 0.048 0.052 0.035 61.1 57.6 0.561 O.593 * Coefficient of variation for 9 determinations. ** Correlation coefficient of 1042 cm-• band versus peptide band intensities.