Effects of Drift Gas Selection on the Ambient-Temperature, Ion Mobility Mass Spectrometry Analysis of Amino Acids

Ion mobility (IM) separates ions based on their response to an electric field in the presence of a drift gas. Because of its speed and sensitivity, the integration of IM and mass spectrometry (MS) offers many potential advantages for the analysis of small molecules. To determine the effects that drift gas selection has on the information content of IM separations, absolute collision cross sections (Ω) with He, N₂, Ar, CO₂, and N₂O were measured for the 20 common amino acids using low-pressure, ambient-temperature ion mobility experiments performed in a radio frequency-confining drift cell. The drift gases were selected to span a range of masses, geometries, and polarizabilities. The information content of each separation was quantified using its peak capacity, which depended on factors contributing to widths of peaks as well as the range of Ω relative to the average Ω for the analytes. The selectivity of each separation was quantified by calculating the peak-to-peak resolution for each pairwise combination of amino acid ions. The number of pairs that were resolved depended strongly on the peak capacity, but the identities of the pairs resolved also depended on the drift gas. Therefore, results using different drift gases are partially orthogonal and provide complementary chemical information. The temperatures and pressures used for these experiments are similar to those used in many IM-MS instruments, therefore, the outcomes of this research are applicable to optimizing the information content of a wide range of contemporary and future IM-MS experiments