Abstract
Efficient ionization of neutral oligosaccharides in negative-ion matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was achieved; harmine (7-methoxy-1-methyl-9H-pyrido[3,4-b]indole) was used as a matrix and ammonium chloride was added as a chloride source to generate chlorinated molecules of neutral oligosaccharide. Increasing the molar amount of ammonium chloride gradually increased the ionization efficiency, which was saturated by adding over 2 molar equivalents of ammonium chloride to the matrix. Ionization efficiency increased when the concentration of salt was high. The results of solid phase fluorescence spectra of mixed crystals indicated that harmine was protonated and formed the hydrochloride salt. Results of ultraviolet absorption spectra showed that harmine hydrochloride absorbed ultraviolet laser irradiation from a nitrogen laser (337 nm) more effectively than harmine, and that ionization efficiency of the chlorinated molecule increased. Harmine hydrochloride was the most effective matrix.
