Figure 1.

Mass spectrometry (MS) imaging workflow including methods of OTCD across MALDI, LESA, and DESI platforms. Following sample tissue collection, thin sections are mounted onto glass slides. From here, OTCD and analysis by reactive DESI do not require further preparation. In LESA, MALDI, and nonreactive DESI platforms, the derivatization reagent is sprayed directly onto the tissue. For MALDI, if the derivatization reagent also serves as a matrix (reactive matrix), no additional step is required. Alternatively, matrix must also be applied to the slide before analysis. Once sample preparation is complete, ionization and MS analysis are carried out by the appropriate instrument. DESI, desorption electrospray ionization; LESA, liquid extraction surface analysis; MALDI, matrix‐assisted laser desorption/ionization; OTCD, on‐tissue chemical derivatization [Color figure can be viewed at wileyonlinelibrary.com]