Chemical imaging of hair by infrared microspectroscopy using synchrotron radiation

For the first time, infrared microspectroscopy with a synchrotron source has been used to characterize human hair before and after bleaching. This high-brightness source allows a lateral resolution approaching the diffract ion limit (a few microns) to be achieved. Thus, 4-micron diameter areas have been analyzed, and chemical imaging of hair cross sections obtained with good contrast. In particular, the variations of the integrated absorbances of the amide stretching vibration (3230 cm(-1)) and CH stretching vibrations (between 3000 and 2800 cm(-1)) as a function of sample position have allowed chemical imaging of the medulla and cuticle. We also studied bleaching of the hair, and we checked different chemical effects as a function of position in the hair cross section. We also observed a non-homogeneous distribution of bonded water. The transformation, due to breakage of a specific chemical group, was observed and spatially characterized. The sulphonate contributions were given special attention and showed non-homogeneous distributions within the hair.