Investigation of human hair using ToF-SIMS: From structural analysis to the identification of cosmetic residues

Abstract

Analysis of human hair using time-of-flight secondary ion mass spectrometry (ToF-SIMS) is particularly challenging because of the high transverse curvature of the hair fiber and the presence of the cuticle scales on its surface, which hampers mass spectrometric imaging. Delayed extraction of the secondary ions combined with a simple planar sectioning of the hair has been used to limit the image artifacts encountered with hair samples, giving access to the desired level of information. In this study, the entire structure of human hair was characterized using ToF-SIMS with longitudinal sectioning. Thus, the authors have examined the inner structure of the hair fiber and obtained chemical information from various regions of the hair. Atomic force microscopy (AFM) was also used to characterize the variation in surface properties that are dependent on the presence of different cosmetic residues on the hair surface. By subjecting a hair with an unknown cosmetic residue to AFM observation combined with principal component analysis of a ToF-SIMS image, the authors were able to identify the type of cosmetic present and to correlate its spectrometric signature with that of the original hair styling product. These results demonstrate the potential of their methodology for the investigation of human hair specimens and for the development of hair styling products in the cosmetic industry. Published by the AVS.