Supplementary information files for "Determination of Collisional Cross Section Using Microscale High-Field Asymmetric Waveform ion Mobility Spectroscopy–Mass Spectrometry (FAIMS-MS)"

Supplementary files for article "Determination of collisional cross section using microscale high-field asymmetric waveform ion mobility spectroscopy–mass spectrometry (FAIMS-MS)"<br><br><b>Rationale</b>: Collisional cross sections (CCS) are an important characteristic of gas-phase ions that are measured using ionmobility-mass spectrometry (IMS). Typically, CCS measurements are performed with drift-tube IMS or travelling-wave IMS.However. in a high-field asymmetric waveform ion mobility (FAIMS) device, ion heating effects make CCS determination morechallenging. This research explores whether CCS can be predicted with microscale FAIMS by using known CCS standards.<br><b>Methods</b>: An Owlstone ultraFAIMS microscale FAIMS spectrometer was coupled to an Orbitrap Exactive mass spectrometer.Two different CCS standard mixtures (tetraalkylammonium halides [TAAHs] and poly-DL-alanine oligomers) were used toevaluate the system's potential to determine CCS. Test peptide bradykinin acetate and substance P were used to evaluate CCSdetermination accuracy for singly and doubly charged peptide species using external calibration with a series of poly-DL-alaninepeptides for +1, +2 charge states.<b>Results</b>: Calibrations with excellent correlation coefficients (R2 = 0.99) for both TAAHs and poly-DL-alanine were obtained.Good accuracy of determination was achieved for bradykinin [M + 2H]2+ with a ± 0.5% difference between experimental andpublished CCS at a dispersion field (DF) strength of 250 Td; the model proved less accurate for bradykinin [M + H]+ (±1.4% at240 Td). The accuracy of determination for the [M + H]+ and [M + 2H]2+ ions of substance P was within ± 5% and ± 3% at 250 Td,respectively, while at higher DF values, accuracy decreased to approximately 5%.<b>Conclusions</b>: Distinct relationships were observed between CCS and transmission CF with both calibrants. Optimum accuracywas obtained at DF 240–260 Td. At lower DF, accuracy is reduced by insufficient resolution of analyte ions from solvent clusteradducts, while at higher DF values, poor transmission becomes a factor. Nevertheless, these data suggest microscale FAIMS canconduct CCS measurements with reasonable accuracy when the compound being measured has similar structural features tothe CCS standards used.© The Author(s) - CC BY 4.0<br>