Mark E. Bier

A tandem quadrupole mass spectrometer for the study of surface-induced dissociation

Abstract A tandem quadrupole mass spectrometer has been built for the study of polyatomic ion/surface collision phenomena. Mass-selected ions collide with a surface at translational energies of 10–100 eV and the ionic products are extracted at an angle of 90° to the incoming beam direction and mass analyzed. Inelastic collisions leading to surface-induced dissociation (SID) give daughter spectra which show excellent precision and agree well with data taken using an earlier hybrid instrument. Large internal energies can be deposited upon surface collisions and this leads to extensive fragmentation of such refractory ions as the pyrene molecular ion. The distributions of internal energies acquired upon collision are estimated from the daughter spectra in appropriate cases such as that of tetraethylsilane molecular ions. From these data, the average internal energy of Et 4 Si +· ions after surface activation is found to vary linearly with collision energy in the range 10–100 eV, with some 16% of the laboratory energy appearing as average internal energy of the organic ion. Comparisons are made with internal energy distributions for gas-phase collisions under single and multiple collision conditions. Ion/surface reactive collisions can be studied using the new instrument while collision-activated dissociation can be performed in addition to or as an alternative to surface-activated dissociation.

Tandem mass spectrometry using an in-line ion-surface collision device

The concept of in-line ion-surface collisions is delineated and the design of a particular device is described. The object of these experiments is to allow ion-surface collisions to occur and their products to be collected while maintaining the normal linear geometry of the mass spectrometer in the collision region. In the device described here, the parent ion beam is electrically deflected from a central conical deflector held on-axis and collinear with the incoming beam and this causes the ions to collide with the surface of an annular target. Daughter ions are then extracted from the surface and mass-analyzed in a second mass analyzer. By appropriate choice of potentials, the beam can alternatively be caused to transit the device without undergoing collision with the target. This allows effects associated with surface collisions to be distinguished from such processes as metastable ion dissociation. The collision device is designed to be applicable to mass spectrometers of various types and to test its versatility it was fitted to a hybrid (BEQ), a tandem quadrupole (QQ) mass spectrometer and a commercial triple quadrupole. In addition to surface-induced dissociation, ion-surface collisions have been observed to result in reflection, chemical sputtering, and reactions with surface adsorbates. These reactions are demonstrated in the BEQ instrument with the parent ions CCl+3 and CH3CN+, respectively. These and other experiments showed that the performance of the in-line device is similar to that achieved when ion/surface collisions are studied with the usual 90° orientation of analyzers although the sensitivity is lower. The average internal energy deposited into the W(CO)+6 ion in an inelastic collision with the surface is ca. 13% of the laboratory collision energy and increases linearly with collision energy up to at least 90 eV. The large energy deposition causes leucine enkephalin, (M + H)+, m/z 556, and the decapeptide angiotensin, (M + H)+, m/z 1297, to show extensive fragmentation upon surface-induced dissociation using the in-line device.