A tandem ion trap/ion mobility spectrometer

A tandem quadrupole ion trap/ion mobility spectrometer (QIT/IMS) has been c onstructed for structural analysis based on the gas-phase mobilities of mas s-selected ions. The instrument combines the ion accumulation, manipulation , and mass-selection capabilities of a modified ion trap mass spectrometer with gas-phase electrophoretic separation in a custom-built ion mobility dr ift cell. The quadrupole ion trap may be operated as a conventional mass sp ectrometer, with ion detection using an off-axis dynode/multiplier arrangem ent, or as an ion source for the IMS drift cell. In the latter case, pulses of ions are ejected fi-om the trap and transferred to the drift cell where mobility in the presence of helium buffer gas is determined by the collisi on cross section of the ion. Ions traversing the drift cell are detected by an in-line electron multiplier and the data processed with a multichannel scaler. Preliminary data are presented on instrumental performance characte ristics and the application of QIT/IMS to structural and conformational stu dies of aromatic ions and protonated amine/crown ether noncovalent complexe s generated via ion/molecule reactions in the ion trap.