Development of an ultra-fast polarity-switching ion mobility spectrometer ready for coupling with supercritical fluid chromatography

Supercritical fluid chromatography (SFC) is an effective method for separating complex samples combining the advantages of both high-performance liquid chromatography and gas chromatography. Owing to its high separation speeds, SFC demands a fast and sensitive detector suitable for a wide range of analytes. Therefore, an ultra-fast polarity switching ion mobility spectrometer (IMS) with extended field-switching ion shutter for simultaneously recording ion mobility spectra in positive and negative polarity and ready for coupling with SFC is presented, adding an additional dimension of separation. Furthermore, the integration of both soft X-ray and UV ionization sources provides the flexibility for chemical gas-phase ionization as well as for direct ionization of analytes. Integrating these features, this work presents an ultra-fast polarity switching IMS with a novel heated emitter chip interface for coupling SFC and examines ion losses during polarity switching using different IMS repetition rates and timing parameters. To demonstrate the performance of the IMS, limits of detection for gas-phase samples were determined for different substances in the positive and negative polarity. Subsequent testing of the coupling between SFC and ultra-fast polarity switching IMS was carried out using a chip-based, miniaturized SFC system with acetylacetone as a model compound that forms positive and negative ions in IMS, demonstrating the simultaneous detection of both ion polarities within one single chromatographic run.