Electrohydrodynamic ionization mass spectrometry of biochemical materials

Electrohydrodynamic ionization mass spectrometry has been applied to a range of biochemical materials dissolved in glycerol with NaI as electrolyte. Sugars (glucose, sucrose, raffinose), nucleosides (adenosine, thymidine, uridine), a tripeptide (glutathione) and an aminocyclitol antibiotic (neomycin) have been analyzed. Unambiguous analysis of a multicomponent solution has been demonstrated. All samples yielded several quasimolecular ions involving either proton or cation attachment to clusters of sample and/or solvent molecules. Unlike other techniques such as field desorption, electrohydrodynamic ionization is not observed to cause fragmentation of sample molecules. The mass spectrometer was operated so as to analyze only those ion clusters which had not undergone decomposition processes; under these conditions, most materials are ionized with similar efficiencies if the total abundance of all characteristic quasimolecular ions is considered. Information regarding the amino acid sequence of glutathione was obtained by thermal pretreatment of the glycerol solution before mass analysis. Positive and negative ion spectra give complementary information which can resolve potential ambiguities regarding the exact composition of quasimolecular ions. Electrohydrodynamic ionization mass spectrometry should be applicable to materials which cannot be ionized by other methods.