Electrospray Low-Pressure Ion Mobility MS

FIGURE 9.2 Schematic diagram of electrospray ionization-ion trap-low-pressure ion mobility spectrometer-time-of-flight mass spectrometer (ESI-IT-IMS-TOF). (From Henderson et al., ESI/ion trap/ion mobility/time-of-flight mass spectrometry for rapid and sensitive analysis of biomolecular mixtures, Anal. Chem. 1999,71,291. With permission.) 

After mobility separation, the ions exit the ion mobility drift tube and are shaped into a ribbon trajectory with a combination of Einzel and DC-quadrupole lenses so that the ion beam traverses the 25-cm long focusing region and passes through a 1.6 X 12.7 mm slit into the source region of a TOF-MS. 

The TOF-MS is positioned orthogonal to the IMS tube so that the ion trajectories in the TOF are at right angles to their trajectories in the IMS. Orthogonal introduction 

In summary, the advantages of low-pressure IMS are that ion trap injection can replace ion gates to improve sensitivity, and ion-focusing devices such as the ion funnel can be employed at low pressure to offset ion diffusion. Due to the complexity and size of the instrument, however, no commercially available low-pressure IMSs with static homogeneous electric fields are interfaced to MSs. Nevertheless, their performance in research laboratories has clearly demonstrated many advantages of coupling IMS to MS. 

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