Aspects of recent developments in ion-trap mass spectrometry

Abstract

Methods which can be used to obtain mass spectra and tandem mass spectra by means of quadrupole ion traps are reviewed and illustrated. High-order (MSn) experiments are described, as is energy-resolved mass spectrometry in which the internal energy deposited upon collision is systematically varied. Ionization methods which can be used in conjunction with ion traps are discussed with special emphasis on experiments in which ions are generated in an external source and injected into the trap for separation and detection. Ion traps are well-suited to on-line monitoring; the performance of membrane probes in these applications is discussed, and detection limits, response times and quantitative accuracy are outlined. Initial attempts to extend the mass range of ion traps have yielded data to more than 45 000 daltons. In addition to being suited to the study of collision-activated dissociation, the experiment on which most applications of tandem mass spectrometry depend, ion traps also allow ion/molecule reactions to be used for these purposes. Use of a pulsed valve to introduce reagent gases in pulses as short as 50 ms facilitates these experiments. Equilibrium conditions are attainable for fast ion/molecule reactions and measurement of equilibrium and rate constants is discussed. Because they combine a range of capabilities, ion traps are well-suited to the study of gaseous ion chemistry, illustrated here by the halomethylation of aromatic compounds, and the competitive dehydration and deamination of α,ω-amino alcohols.