PNNL

Abstract

Over the last few years, structures for lossless ion manipulations (SLIM) have used radiofrequency (RF) fields to confine ions and traveling wave (TW) electric fields to move ions over long serpentine ion paths, and have also allowed for extended serpentine ultralong paths with extended routing (SUPER) separations that can be further enhanced by routing ions through multiple passages through the same path. Such SLIM SUPER ‘multi-pass’ separations provide unprecedentedly high ion mobility resolving powers but are ultimately limited in their ion mobility range to prevent ion ‘lapping’. To achieve ultrahigh resolution separations over a broad mobility range, we have developed a new multilevel SLIM possessing multiple stacked serpentine paths. Ions are transferred between SLIM levels through apertures in the SLIM surfaces. The initial multilevel SLIM module incorporates four levels and three inter-level passages, providing a total path length of 43.2 m. Using the full path length and helium buffer gas, high resolution separations were achieved for Agilent tuning mixture phosphazene ions over a broad mobility range (K0 ˜ 3.0 to 1.2 cm2/(V*s). High sensitivity was achieved using ‘in-SLIM’ ion accumulation over an extended trapping region of the first SLIM level. High transmission efficiency of ions over a broad mobility range (e.g. K0 ˜ 3.0 to 1.67 cm2/(V*s)) was achieved, with transmission efficiency rolling off for the lower mobility ions (e.g. K0 ˜ 1.2 cm2/(V*s)). Resolving powers of up to ~400 were achievable using all four ion levels to separate reverse peptides (SDGRG1+ and GRGDS1+). A complex mixture of phosphopeptides showed similar coverage could be achieved using one or all four SLIM levels, and doubly-charged phosphosite isomers not significantly separated using one SLIM level were well resolved when four levels were used. The new multilevel SLIM technology thus enables significantly wider mobility range ultrahigh-resolution ion mobility separations and expands on the ability of SLIM to obtain improved separations of complex mixtures.