Influence of the Calculated Analyte Structure on the Quality of Theoretical ion Mobility Calculations

Ion mobility spectrometry is a well-known technique used to identify and analyze substances in environmental monitoring by their characteristic ion mobility. In typical scenarios, there is only insufficient information available regarding what substances will be present. Therefore, the IMS device has to show a great flexibility regarding what it can safely detect. In recent years, great success was achieved on the experimental side, and the selectivity, i.e. resolving power, could be increased. Similarly, there has been great progress in theoretical ion mobility calculation approaches, which can support the identification task in critical cases. One of these critical cases is the presence of analyte dimers, where an analyte leads to more than one signal in the IMS spectrum. The theoretical ion mobility calculation is typically based on calculated analyte geometries with a local energy minimum. Since there are many options for local minima in complex structures, we have analyzed here to what extent these structures lead to different calculated mobilities in the case of the environmentally important analytes toluene diisocyanate in a cluster with formic acid as well as the 2-chlorophenol dimer.