The SIFT and FALP techniques; applications to ionic and electronic reactions studies and their evolution to the SIFT-MS and FA-MS analytical methods

Abstract

Flow tube reactors coupled with quantitative mass spectrometry have made, and continue to make, major contributions to gas phase ion–molecule chemistry, to recombination and electron attachment studies and, most recently, to gas phase trace gas analysis. This paper briefly reviews the concepts and principles of operation of flowing afterglow, FA, and flowing afterglow Langmuir probe, FALP, plasma reactors, and selected ion flow tube, SIFT, ion swarm reactors for the study of the above processes. This paved the way to our recent developments of the novel analytical methods that we call selected ion flow tube mass spectrometry, SIFT-MS, and flowing afterglow mass spectrometry, FA-MS. A time line of these developments during the last fifty years is presented. It is shown how exploitation of FA and SIFT has provided the essential kinetics data that allow modelling of the ion chemistry of naturally occurring plasmas, especially the terrestrial ionosphere and interstellar gas clouds, and has greatly facilitated the developments and evolution of SIFT-MS and FA-MS, which are contributing to the science of ambient trace gas analysis. The wide ranging applications of SIFT-MS are alluded to whilst focusing on the successful direct real time quantitative analysis of volatile metabolites in exhaled breath forcibly demonstrating the unique analytical features of SIFT-MS.