Abstract
Hair can record chemical information reflecting our living conditions, and, therefore, strands of hair have become a potent analytical target within the biological and forensic sciences. While early efforts focused on analyzing complete hair strands in bulk, high spatial resolution mass spectrometry imaging (MSI) has recently come to the forefront of chemical hair-strand analysis. MSI techniques offer a localized analysis, requiring fewer de-contamination procedures per default and making it possible to map the distribution of analytes on and within individual hair strands. Applying the techniques to hair samples has proven particularly useful in investigations quantifying the exposure to, and uptake of, toxins or drugs. Overall, MSI, combined with optimized sample preparation protocols, has improved precision and accuracy for identifying several elemental and molecular species in single strands of hair. Here, we review different sample preparation protocols and use cases with a view to make the methodology more accessible to researchers outside of the field of forensic science. We conclude that—although some challenges remain, including contamination issues and matrix effects—MSI offers unique opportunities for obtaining highly resolved spatial information of several compounds simultaneously across hair surfaces.
Highlights
We present how different washing and cutting methods have been used in hair-sample preparation to minimize chemical losses and to improve the analytical potential that these techniques have to offer
The decontamination process is critical in hair analysis, especially within the field of forensic science
When the focus of the analysis is chemicals on the hair surface, like in hair cuticle analysis, developing appropriate decontamination protocols is especially important for obtaining reliable results
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Such bulk analyses are complicated by the fact that hair products and dust can introduce exogenous chemical signals and interfere with the overall interpretation [10,12] Preparation procedures, such as different washing steps, have been employed to remove superficial contaminants. MSI methods, including secondary ion mass spectrometry (SIMS) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), have proven to be viable alternatives for mapping the chemical and elemental landscape of individual hair strands [16,17]. Human hair fibers are covered by multiple layers of cuticle cells that protect the inner structure from damage caused by external factors, including environmental agents, cosmetic treatments, and industrial processes [19] This inner structure is mainly made up of the cortex, which consists of several intermediate keratin filaments, cross-linked with keratin-associated proteins via extensive disulfide bonds [20,21]. Main layers of aofhair strand—the cuticle, cortex, and medulla
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