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.