Mass spectrometric analysis of cardiac glycosides by the desorption/ionization technique potassium ion ionization of desorbed species

Characterization of the primary thermal degradation processes of peptides using the mass spectrometric technique K(+)IDS, K (+) ionization of desorbed species

The mass spectrometric technique of K(+) ionization of desorbed species, K(+)IDS, is used here to characterize the primary thermal degradation chemistry of small peptides. In this technique, a small amount of a compound is rapidly heated in the condensed phase. Desorption of the intact molecule can occur. Also, thermal degradation products are formed which quickly desorb as well, rather than remain on the surface and undergo subsequent chemistry. The desorbed molecules form adducts with gas phase K(+) ions, and a mass spectrum is obtained. Deuterium labeling experiments, and the use of derivatizing reagents, allows for the thermal degradation chemistry of small peptides to be elucidated. Apparently, skeletal bond cleavages are accompanied by H-shifts, although the hydrogen atoms shift from "remote" sites, brought into close proximity with the fragmenting skeletal bond via secondary interactions. Experimental results are presented that allow for correlations between thermal degradation chemistry and the resulting K(+)IDS mass spectra to be made.

Injection of reagent ions into the selvedge region in fast-atom bombardment mass spectrometry

A divided probe that incorporates a potassium aluminosilicate glass target and an analyte/glycerol matrix target, spatially separated, was used to inject potassium ions (K(+)) into the high-pressure "selvedge" region formed above the analyte/glycerol matrix target during fast-atom bombardment (FAB); [M+K](+) adduct ions that represent the types of gas-phase neutral molecules present in the selvedge region are observed. Computer modeling assisted in designing the divided target and an additional ion optical element for the FAB ion source to optimize interactions between K(+) ions and the desorbed neutral molecules. The capability of injecting K(+) ions into the FAB experiment has utility in both mechanistic studies and analyses. Experimental results here are consistent with a model for the desorption/ionization processes in FAB in which some types of neutral analyte molecules are desorbed intact and are subsequently protonated by glycerol chemical ionization. Unstable protonated molecules undergo unimolecular decomposition to yield observed fragment ions. The use of K(+) cationization of analytes for molecular weight confirmation is demonstrated, as well as its utility in FAB experiments in which mixtures are encountered.

Chloride attachment negative-ion mass spectra of sugars by combined liquid chromatography and atmospheric pressure chemical ionization mass spectrometry

A method has been developed for the rapid determination of sugars, including molecular weight measurements, using high-performance liquid chromatography coupled with negative-ion, atmospheric-pressure chemical-ionization mass spectrometry. The chromatography was carried out on a 250 x 4 mm I.D. column packed with 7 microns NH2-silica. The mobile phase consisted of a high percentage of methanol or acetonitrile with a small amount of chloroform. During the mass spectrometry, a strong base is formed from the polar solvent molecules by corona discharge, followed by ion-molecule reactions in the chemical ionization ion source (e.g. the methoxy anion is formed from methanol). This strong base reacts with the chloroform, generating chloride ions, which in turn react with the neutral sugar molecules as they elute from the chromatograph. The chloride ion and sugar interactions yield chloride-attachment ions, which are further stabilized by successive collisions. In this method, authentic monosaccharides and some oligosaccharides show dominant quasi-molecular ions, [M + Cl]-, with little fragmentation, and its particularly useful for the molecular weight determination of sugars.

Mechanistic considerations of the protonation and fragmentation of highly functionalized molecules in fast atom bombardment: High resolution mass spectrometry and tandem mass spectrometry analysis of the ions formed by fast atom bombardment of digoxin and related cardiac glycosides

High resolution mass spectrometry and tandem mass spectrometry analyses of the major ions of digoxin formed by fast atom bombardment are presented and discussed to investigate the mechanisms through which fragment ions are formed. Similar cardiac glycosides are also analyzed to provide support for the proposed fragment assignments. Remote site fragmentation with the charge localized on the aglycone portion of the molecule may provide an explanation for the fragment ions observed in these studies because the majority of these ions contain the aglycone portion of the molecule. The results obtained parallel previously reported results from an ammonia chemical ionization mass spectral study of cardiac glycosides. (J Am Soc Mass Spectrom 1990, 1, 455-472).