Polyatomic ion/surface collisions: New methodology in tandem mass-spectrometry

Abdul Mabud MD., Purdue University

Abstract

The excitation of a gas phase ion to induce fragmentation is an important aspect of tandem mass spectrometry. Although excitation and fragmentation of polyatomic ions is typically accomplished upon collision with gaseous targets, limitations in energy deposition in an ion call for alternative methods of excitation. Therefore, investigations have been made by using metal surfaces as collision partners to activate polyatomic ions by using ions of 20-150 eV kinetic energy. Among the phenomena investigated are dissociation of the polyatomic ions upon collision with metal surfaces. The extent of dissociation can be controlled by selection of the impact energy. Collision with a surface gives rise to a narrower range of internal energies than do the corresponding ion/gaseous target collisions. Very large amounts of energy can be deposited in polyatomic ions upon collision with a metal target. Even at modest laboratory kinetic energies, the average internal energy deposited in ion/surface collisions exceeds that in gaseous collisions. Charge-exchange of multiply-charged species at the surface also occurs. Although simple charge exchange is observed, dissociative charge exchange is dominant in the cases studied. Dissociation and charge exchange of polyatomic ions in ion/surface collision are also accompanied by reactive collisions between organic ions and gas-covered metal surfaces. These processes include abstraction of H$\sp{\cdot}$, 2H$\sp{\cdot}$, 3H$\sp{\cdot}$ atoms and a CH$\sb3\sp{\cdot}$ group from the surface by the incident ions. Utility of polyatomic ion/surface interaction technique for isomeric ion characterization has also been investigated. The ion/surface interaction technique appears to have excellent ability to distinguish isomeric ions. One advantage of SID in isomeric ion characterization lies in the fact that reactive collisions occur simultaneously and add a new dimension of information to the daughter spectra recorded. The hydrogen and methyl radical abstraction reactions assist in distinguishing closely related isomeric ions. In the cases examined, ion structures could be deduced from the reactive collision and dissociation reactions observed.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry

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