IMS-MS studies based on coupling a differential mobility analyzer (DMA) to commercial API-MS systems

Recent progress in adding a mobility dimension to preexisting API-MS systems without modifying the MS itself is discussed, based on inserting a differential mobility analyzer (DMA) as part of the MS's atmospheric pressure ion source. Design criteria leading to high DMA resolving power R and transmission efficiency eta are discussed. Various DMA prototypes have been interfaced to several triple quadrupoles, a single quadrupole and a quadrupole-TOF, all demonstrating R>50 and eta > 50%. We obtain two-dimensional DMA-MS spectra of the multiply charged clusters formed in electrosprays of concentrated solutions of tetrahexylammonium bromide (A(+)Br(-)). These reveal systematic loss of (ABr)A(+) fragments from unstable multiply charged clusters, and provide mobility measurements in air on mass resolved (ABr)(n)(A(+))(z) clusters with n > 100 and z up to 10. Well-defined bands of ions not individually resolved are clearly visible at considerably larger n and z values. (C) 2010 Elsevier B.V. All rights reserved.