Origins of the proton in the generation of protonated polymers and peptides in matrix-assisted laser desorption/ionization

In this paper, various possible sources of protons for protonation of polymer and peptide molecules under matrix-assisted laser desorption/ionization conditions were studied by using a deuterium labeling method,It was demonstrated that exchangeable protons from either carboxylic acid or hydroxyl groups of the matrix were important, but not essential, for protonation of the analyte, For a nitroanthracene matrix, the non-exchangeable protons from the matrix and the exchangeable protons from the solvent (and possibly from the analyte) were also shown to contribute protons for the formation of protonated molecule-ions.