ESI-HiKE-IMS reference platform for IMS to investigate field-dependent effects such as fragmentation, cluster association and dissociation, and to determine the alpha functions of larger analyte moleculeser Analytmoleküle

Compared to mass spectrometry, ion mobility spectrometry offers an almost orthogonal ion separation, so that ion mobility spectrometers (IMS) are increasingly coupled with mass spectrometers (MS) as a further separation dimension. Such IMS-MS are particularly important in the analysis of biochemical samples such as lipids, sugars, metabolites and peptides, and usually equipped with an electrospray ionization (ESI) source. Unlike the mass-to-charge ratio, the ion mobility depends on the device parameters. In particular, the ion mobility depends on the effective ion temperature and therefore on the absolute temperature and the reduced electric field strength E/N, which is the ratio of the electric field strength E to the number density N. The IMS established in MS today, such as TWIMS, TIMS and DMS, use high alternating electric fields due to the separation principle or for ion focusing, so that the ion mobility constantly changes during the separation process in the IMS. Thus, the ion mobility cannot be given for a specific E/N without precise knowledge of the field-dependent processes. Since the field-dependent processes are ion-specific, calibration with standards is also not solving this issue. However, interpretation of experimental results and reproducibility of TWIMS, TIMS and DMS can be significantly improved if the ion-specific, field-dependent processes are quantified.

Therefore, this project aims to develop a reference platform for investigating the ion mobility at defined E/N over a wide range. The high-energy ion mobility spectrometer (HiKE-IMS) developed in previous work serves as the basis, but is currently neither able to analyze larger molecules, such as lipids, sugars, metabolites and peptides, nor does it allow small E/N, as required for the determination of the "low-field" ion mobility and the complete alpha function. Therefore, an ESI-HiKE-IMS with an E/N from less than 10 Td to 120 Td and a new approach for accelerated evaporation of the charged droplets generated during ESI by high E/N and thus high effective droplet temperatures will now be developed for the first time. This ESI-HiKE-IMS is then coupled to a MS via an energy-neutral ion interface to thoroughly investigate the ion mobility and the field-dependent cluster association and dissociation as well as fragmentation of the relevant standards for TWIMS, TIMS and DMS. In particular, the alpha functions of several polyalanines in different charge states are to be investigated, as these are frequently used for the calibration of peptides. Finally, the established calibration recommendations are to be re-evaluated on the basis of the data obtained.