Experimental Evaluation and Optimization of Structures for Loss less Ion Manipulations for Ion Mobility Spectrometry with Time-of-Flight Mass Spectrometry

We report on the performance of structures for lossless ion manipulation (SLIM) as a means for transmitting ions and performing ion mobility separations (IMS). Ions were successfully transferred from an electrospray ionization (ESI) source to the TOF MS analyzer by means of a linear SLIM, demonstrating lossless ion transmission and an alternative arrangement including a 90 degrees turn. First, the linear geometry was optimized for radial confinement by tuning RF on the central rung electrodes and potentials on the DC-only guard electrodes. Selecting an appropriate DC guard bias (2-6 V) and RF amplitude (=160 Vp-p at 750 kHz) resulted in the greatest ion intensities. Close to ideal IMS resolving power was maintained over a significant range of applied voltages. Second, the 90 degrees turn was optimized for radial confinement by tuning RF on the rung electrodes and DC on the guard electrodes. However, both resolving power and ion transmission showed a dependence on these voltages, and the best conditions for both were >300 Vp-p RF (685 kHz) and 711 V guard DC bias. Both geometries provide IMS resolving powers at the theoretical limit (R similar to 58), showing that degraded resolution from a racetrack effect from turning around a corner can be successfully avoided, and the capability also was maintained for essentially lossless ion transmission.