Doctoral Dissertations

Date of Award

5-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Kelsey D. Cook

Committee Members

John Bartmess, J.Q. Chambers

Abstract

Surface activity effects in fast atom bombardment (FAB) and liquid secondary ion mass spectrometry (LSIMS) were investigated using two quaternary ammonium cations. It was shown that the intensity of tetradecyltrimethylammonium (TTA&sup+;), a surface active cation, Initially strong and then decreased over the lifetime of the sample. The FAB signal. from tetraethylammonium (TEA&sup+;), a non-surface active quaternary ammonium cation, was shown to be initially weak followed by a short lived burst of high intensity prior to the end of the experiment. The reasons for this behavior were determined using a secondary ion imaging instrument to characterize the ton emission from the surface of the sample. The images revealed that TTA&sup+; yielded relatively uniform signal intensity from across the entire surface of the sample, while TEA&sup+ yielded non-uniform secondary ion emission across the surface of the sample. The explanation of the non- uniform TEA&sup+; emission was based on a Marangoni force. Marangoni forces drive less surface active solutes to the periphery of a sample. The TTA&sup+; signal was initially strong because of complete surface coverage from the beginning of the experiment. The TEA&sup+; signal was strong late in the experiment, because that when the region of intense TEA&sup+; emission (due to changes in sample size) comes into the region of the source where ions analyzer. accepted into the

A new micro-electrospray (ES) source developed. The new source was tested using continuous infusion and capillary electrophoresis to deliver solution the emitter. The new source used a small inner diameter fused.silica capillary with mechanically shaped conical tip. The tip chemically treated with a mercaptan reagent to improve the adhesion of a vapor deposited gold layer. These capillaries were shown to withstand over 100 hours of operation, spray a variety of highly conductive aqueous and non aqueous solutions, and to withstand harsh chemical treatment. The capillaries. were also tested spectrometrically. Under continuous infusion conditions, as little as seven attomoles of cytochrome C was detected from an aqueous solution using flow rates less than 1 µl/minute. The charge state distribution of cytochrome C is known to change in the presence of methanol (methanol denatures cytochrome C). The extent of denaturation Investigated using solutions containing various amounts of methanol. Based on preliminary observations, the higher charge states of cytochrome C appear to be more heavily solvated than the lower charge states. The source was also evaluated as components of capillary electrophoresis/ES interface. The four peptide aqueous mixture were successfully separated and detected using the micro-ES source.

EH MS was used to probe the preferential solvation of the proton in mixed solvent system containing 95/5 (v/v) water/glycerol. The EH source used previously sample glycerol solutions was modified to contain a fused silica capillary to deliver aqueous (volatile) solutions to the emitter region in95/5 (v/v) water/glycerol solution containing 40 mM HCI, the most intense peaks in the spectrum are the protonated glycerol dimer ([G&sub2; + H]&sup+;) and trimer ([G³ + H]&sup+). This indicates preferential solvation of the proton by glycerol, andis in good agreement with known gas and solution phase chemistry of the solvents. The relative abundance of water clusters differed markedly from that reported in the literature for the gas-phase hydration of the proton: It Was therefore inferred that the distribution may reflect solution phase rather than gas phase chemistry.

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