Doctoral Dissertations

Date of Award

8-1994

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Kelsey D. Cook

Committee Members

Al Tuinman, John Bartmess

Abstract

This work makes comparisons among electrohydrodynamic (EH) mass spectrometry (MS), fast atom bombardment (FAB) MS, and liquid secondary ion MS (LSIMS). BHMS was used to establish the role of solution chemistry on the formation of benzyl cations (R+). The abundance of R+ in FAB and EH mass spectra correlated with solvent polarity. Two possible explanations involve solution chemistry. Solvolysis and fragmentation from an ion-molecule complex may occur in polar solvents. Mass transport effects on sensitivity in EHMS, FAB MS, and LSIMS were investigated by observing the sampling behavior of a mixture of tetraalkylammonium salts. Diffusion-limited mass transport in EH caused a decrease in signal intensity over time for the heavier, more slowly diffusing ions. Increasing sample flow rate (within limits imposed by discharge within the ion source) led to improved signal intensities for the heavier ions during 30 minute acquisitions. With FAB and LSIMS, ions were sampled in the order of decreasing hydrophobicity. This behavior occurred even among non-surface active components of the mixture. This was attributed to mass transport caused by a combination of the effects of surface forces and glycerol droplet depletion due to evaporation and sputtering. Estimates of average molecular weight (Mn) of some liquid polymers from FAB and EH mass spectra were generally lower than those from LD. Higher estimates of Mn were obtained from FAB with m-nitrobenzyl alcohol (NBA) matrix. One EH mass spectrum obtained with a novel EH ion source which includes a glass capillary section contained peaks due to loss of water from protonated adducts. MS/MS of selected protonated oligomers of these liquid polymers revealed that high mass and low mass oligomers fragmented to give stable low mass product ions. A 3,5-dimethylpyrazole ring versus an OH end group produced more abundant fragment ions. This was attributed to strong attachment of H+ to the ring. A higher collision energy produced more abundant low mass ions from a multi-step, depolymerization mechanism. Beam-induced damage in FAB and LSIMS spectra of methylene blue in glycerol solution was used to calibrate primary beam flux (or beam density). The FAB gun flux was found to depend strongly upon the condition of the electrodes within the gun.

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