Application of FT-IR Step-Scan Photoacoustic Phase Modulation Methods to Keratin Fibers

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Abstract
Step-scan FT-IR/PAS is shown to be a powerful tool for the nondestructive analysis of keratin fibers. Depth profiling studies were performed either by varying the optical velocity of the interferometer (scanning FT-IR/PAS depth profiling) or by a phase modulation method, utilizing a lock-in amplifier to separate the surface and bulk components of the signal phase. Both methods were shown to be capable of distinguishing spectroscopically between the cuticle and cortex of wool and hair fibers, the different spectral features being consistent with the differences in protein composition between these components. Phase-modulated spectra exhibited improved signal-to-noise ratios, with relatively little interference from saturation effects, compared with scanning FT-IR/PAS depth profile spectra.