Date: 13 Jun 2003

Gas-Phase Conformations: The Ion Mobility/Ion Chromatography Method

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Ion mobility spectrometry coupled to mass spectrometry provides a powerful tool to explore the three-dimensional shape of polyatomic ions. Applications include the investigation of cluster ion geometries and conformations of flexible molecules such as biopolymers and synthetic polymers. The ion structure is obtained by measuring collision cross sections in a high pressure drift tube filled with helium and comparing it to model structures obtained by various theoretical methods such as molecular modeling and electronic structure calculations. The temperature of the drift tube is generally adjustable (typically from 80 to 800 K) providing a unique opportunity to address topics such as the thermal motion of floppy molecules, the unfolding process of folded structures, the kinetics of structural interconversion, and the kinetics of dissociation processes. In addition, the ion mobility instrumentation can be used to obtain thermochemical data of ligand addition reactions, giving important additional information about the polyatomic ions under investigation. The theoretical background and the concepts of these ion mobility based experiments and the instrumentation employed are briefly reviewed in this chapter. Furthermore, some detailed examples and a very brief summary of selected applications found in the literature are given.