U-Shaped Mobility Analyzer: A Compact and High-Resolution Counter-Flow Ion Mobility Spectrometer

In recent years, there has been a rapid increase in the use of counter-flow-type ion mobility spectrometers (IMS) due to their improved resolution and functionality. In this study, we developed a new type of counter-flow ion mobility device named the U-shaped mobility analyzer (UMA) for coupling with a mass spectrometer, where the analyte ions could travel along a gas flow in the first channel of the UMA device and then against a gas flow in the second channel of the device. Hence, a mobility band-pass filter was formed by setting different electric fields in the two channels, which enables high-resolution mobility selection of analyte ions. A resolution of ca. 180 was achieved for singly charged small organic molecules, and a resolution of up to ca. 370 was achieved for multiply charged +15 myoglobin. It was thus demonstrated that this filtering function can greatly enhance the dynamic range of an IMS-MS instrument, particularly favoring targeted analysis in complex matrices. Alternatively, the analyte ions could be operated in a so-called trap-scan mode in which ions were trapped first in one of the channels and released sequentially for mobility analysis with an even higher resolution (ca. 210 for singly charged small organic molecules and ca. 590 for +15 myoglobin). Overall, this new UMA device would enable many new applications in omics studies with its high resolution and dynamic range, especially when using the filter-scan mode for scrutinizing analytes with very low concentrations under high chemical backgrounds.