THE DEVELOPMENT AND APPLICATION OF MASS SPECTROMETRIC METHODS TO MOLECULAR ANALYSIS

STEVE EDWARD UNGER, Purdue University

Abstract

Developments which extend the range of compounds amenable to mass spectrometric analysis and the information obtained by mass spectrometric methods are presented, including the use of mass spectrometry/mass spectrometry (ms/ms), secondary ion mass spectrometry (SIMS), and laser desorption mass spectrometry (LDMS). The use of mass spectrometry/mass spectrometry, specifically mass-analyzed ion kinetic energy spectrometry (MIKES), to mass-select a given ion from a complex mixture and identify it by energy analysis of its fragment ions has identified known natural products such as psilocybin, ergosterol, and tetrahydroisoquinoline alkaloids directly from plant materials or extracts. Considerable structural information is provided from the MIKE spectrum which often allows new natural products to be characterized without their actual isolation or serves to distinguish isomeric forms of ions in complex mixtures. When ions representative of the analyte cannot be obtained by conventional ionization methods, SIMS or LDMS may be used to generate intact molecular species. Nonvolatile, thermally labile compounds such as organic salts are identified at picogram levels by SIMS. Best sensitivity is achieved when the analyte exists as a charged species since the relatively inefficient ionization step is obviated, therefore, the addition of acid to the analyte to enhance positive ion mass spectra was used for certain compounds. Alkylated nucleosides may be identified in isolated form, or in relatively well-defined mixtures. By the addition of an internal standard to a hydrolysate mixture of a modified nucleoside, quantitation was achieved using SIMS. Many compounds may be characterized directly from complex mixtures, however, chromatographic separation prior to analysis improves the identification. Paper and thin-layer chromatograms have been imaged for separated constituents by ion bombardment of the chromatogram. Using this procedure, choline and muscarine were detected in an extract of Inocybe napipes. Ionization events in SIMS are delineated, and comparisons are made with other desorption/ionization methods such as field desorption, laser desorption, plasma desorption, and fast-atom bombardment. Direct comparisons are made between SIMS and LDMS using both a quadrupole mass spectrometer and a MIKE spectrometer. The application of SIMS to identify surface and reaction intermediates which are comprised of both organic species and metal ions is presented. Reactions observed from analysis of adduct ions seen in SIMS are reproduced in a chemical reactor, demonstrating the use of molecular SIMS to predict new surface chemistry rather than simply monitor surface changes which have occurred during reaction.

Degree

Ph.D.

Subject Area

Analytical chemistry

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