INTERACTION BETWEEN HAIR PROTEIN AND ORGANIC ACID 145 T""" I 0.03 E 0.025 u 0 "- � LO � co Q) u C co ..c L.. 0 en ..c ( 0.02 0.015 0.01 0.005 0 0 20 40 60 TI min Figure 4. Absorbance of the water band (5170 cm - 1 ) plotted against the treatment time, T. THE SYNCHRONOUS 2D CORRELATION MAP 80 Figure 6 displays a synchronous 2D NIR correlation map of the hair, constructed from the treatment time-dependent (0, 20, 40, and 60 min) spectral variations in the 5 300- 4750 cm- 1 region. The one-dimensional spectra drawn at the top and at the left side of the 2D map are reference spectra obtained by averaging the spectra set. The synchronous correlation spectrum represents the simultaneous or coincidental change of spectral intensity variations measured at v 1 and v 2 : here, v 1 and v 2 are spectral variables (wavenumbers in this paper). A synchronous spectrum is symmetrical with respect to the diagonal line (dashed line). The obtained synchronous correlation map is characterized by two autopeaks ( on the diagonal line) near 5170 and 4890 cm - 1 and cross peaks located at the off-diagonal positions between them. The intensity of autopeaks of a synchronous correlation spec- trum represents the overall extent of dynamic fluctuations of spectral signals (12,16). Therefore, it is found that the change in the water band and the protein band is large. The cross peaks shows the relation between the 5170 cm- 1 and 4890 cm -l bands. The 51 70 cm - l is almost at the center of the water band, but 4890 cm - l is a little deviated

146 Q) +-' ·;;::: Q) "'C "'C C N 4950 JOURNAL OF COSMETIC SCIENCE 4900 4850 4800 4750 Wavenumber/ cm- 1 Figure 5. Second derivaties of the spectra shown in Figure 3 in the 4950-4750 cm- 1 region. Thin solid line: untreated hair. Dotted line: hair treated with MA/BOE/ethanol solution for 20 min. Dashed line: hair treated for 40 min. Thick solid line: hair treated for 60 min. to the higher wavenumber from the center of the protein band. This suggests the existence of other components, having lower wavenumbers in the protein band, which are to be identified in the following asynchronous 2D correlation study. THE ASYNCHRONOUS 2D CORRELATION MAP The asynchronous cross peaks develop only if the basic trends of dynamic spectral variations observed at two different wavenumbers of the cross peaks are dissimilar (12,16). Figure 7 depicts an asynchronous 2D NIR correlation map corresponding to the synchronous map of Figure 6. The wavelength range is limited from 4950 to 4750 cm- 1 for the sake of detailed analysis of the protein band here. From the asynchronous cross