INTERACTIONS OF POLYATOMIC IONS WITH GASES AND SURFACES (MASS SPECTROMETRY, COLLISIONAL ACTIVATION, ION SCATTERING, STRUCTURES)

MICHAEL JAMES DEKREY, Purdue University

Abstract

The excitation of a gas phase ion to induce fragmentation is a central aspect of tandem mass spectrometry. The excitation caused by collision with a variety of neutral gases and with a metal surface is studied as a function of collision energy. The gas phase collision event is applied to distinguish isomers and to allow rapid quantitation of an homologous series of compounds. The hybrid (BQ) tandem mass spectrometer has been modified to provide ion surface collisions which are shown capable of providing significantly more excitation than gas phase collisions. In addition, the modified instrument design is capable of a wide variety of other experiment types. An extension of the standard addition procedure is applied to the quantitation of an homologous series using parent scans, a tandem mass spectrometry scan mode. Quantitation using this technique is shown to be rapid, applicable to compounds for which standards are unavailable, and to produce reasonably accurate results. A variation in collision energy is known to transfer a varying amount of internal energy into the ion at low collision energies. One experiment which exploits this variation has been called Energy Resolved Mass Spectrometry, ERMS. The application of ERMS is shown to be advantageous in the differentiation of several isomeric C(,5)H(,8) ions which were difficult or impossible to distinguish by their daughter spectra alone. The ERMS technique is also applied to study the effect the target gas has on the internal energy deposited during collision. This effect is shown to be approximately equal to the difference in the center-of-mass kinetic energy for low energy excitation, but there exists a further mass effect for higher energy excitation. A metal surface is tested as a collisional partner and is shown to have several advantages over conventional gaseous targets in imparting internal energy. These advantages include both a narrower internal energy distribution and broader range of energies than is available from conventional CID. In addition, a variety of new experiments are possible because of this new instrumental configuration.

Degree

Ph.D.

Subject Area

Analytical chemistry

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