ABSTRACT

In previous chapters, mobility spectrometers have been described as analytical instruments that are used independent of other chemical equipment to measure the chemical composition of a sample. Those descriptions emphasize the attractions of IMS analyzers as portable, fast, convenient, rugged, and economical. However, IMS drift tubes may be combined with other chemical instruments, and such combinations result in synergistic benefits. When a mobility spectrometer is combined with a gas chromatograph, the chemical information obtained and the characteristics of the measurements are improved by more than the individual results put together. Mobility spectra can be obtained for column effluent throughout a chromatographic separation, providing, from the measurement, additional analytical information, which is somewhat orthogonal to the retention timescale. Thus, mobility spectra enrich a chromatographic separation through a second dimension of mobility. However, improvements in the quality and value of the mobility spectrometer response result from the prefractionation of a complex sample and, ideally, the delivery of components as individual constituents to the IMS analyzer. When prefractionation is done, the ion chemistry in the reaction region is simplified and demands on ion separations in the drift tube are reduced. In this way, the chromatograph enhances the analytical value of the mobility spectrometer. Thus, the combination of a chromatograph and a mobility spectrometer is mutually beneficial and provides a data set that is suitable for advanced data handling. A final attraction for the use of both a chromatograph and an IMS analyzer is that the interface is inexpensive and uncomplicated because the IMS drift tube is operated at ambient pressure. This alleviates the demands of interfacing vacuum and ambient pressure as found in gas chromatography/ mass spectrometry (GC/MS) or liquid chromatography/mass spectrometry (LC/MS) instruments.