“…Chemical derivatization is frequently used as a strategy for increasing ion yields, improving chromatographic performance, and facilitating structure identification in gas chromatography tandem-mass spectrometry and liquid chromatography-mass spectrometry (LC)-MS analysis. On-tissue chemical tagging of unionizable target analytes with easily ionized moieties is an alternative means of enhancing ionization efficiency, sensitivity, and specificity in MSI experiments. − On-tissue chemical derivatization (OTCD)-MSI methods targeting fatty acids, steroid hormones, thiol peptides, amino acids, neurotransmitters, and drugs have been developed, providing important tools that are used to determine the temporal and spatial fate of these metabolites in pathological processes. − For example, Wu et al developed an electrospray-assisted OTCD method using 2-pyridinemethanamine as the derivatization reagent and mapped the distribution of endogenous fatty acids in brain tissue using OTCD-MALDI-MSI. Guo et al developed a laser-assisted tissue transfer (LATT) technique to improve the tissue derivatization of small molecules and imaged 69 derivatized metabolites, including neurotransmitters, amino acids, dipeptides, and steroids, in the rat brain using LATT derivatization with 4-hydroxy-3-methoxycinnamaldehyde and Girard’s reagent T (GT).…”