Protonation isomers of highly charged protein ions can be separated in FAIMS-MS

Differential Ion Mobility Separations of d/l Peptide Epimers

“…The singular difficulty for W peptides at both z probably stemmed from the d -aa at the C-terminus, negligibly affecting the overall ion geometry assessed by linear IMS. Good resolution of the same species by FAIMS illustrates its orthogonality to linear IMS − and capability (previously noted for proteins) , to delineate the peptide isomers with shared global conformations but deviations in local detail. The pair with d / l variation at the N-terminus was also resolved baseline.…”

An atmospheric pressure ion funnel with a slit entrance for enhancing signal and resolution in high resolution differential ion mobility mass spectrometry

“…The integration of the slit-APIF concept into high resolution DMS could be particularly useful in the analysis of ions with higher masses and m / z values that are generally more difficult to analyse in high resolution DMS owing to their low ion transmission efficiencies compared to ions at lower masses. For example, using ESI and high resolution DMS-MS with a conventional DMS-capillary interface, we previously obtained maximum peak ion counts of ∼10 4 for protonated carbonic anhydrase ions (∼29 000 kDa, 26–38+) at the optimal CV, 19 which was far lower than that obtained for protonated peptide ions (ion counts of 10 5 –10 6 ; ∼1800 kDa, 3+ and 4+) 16 at comparable concentrations (low μM). An adjustable slit gap width could potentially be used to determine an optimal trade-off between sensitivity and resolution without the need to change the dispersion voltage, flow rate, or the carrier gas composition, which are key factors in DMS that affect both the peak position and resolution.…”

“…Furthermore, the electrical breakdown limit of gases and hence the maximum allowable dispersion voltage decreases by using carrier gases with lower molecular weight and for lower flow rates. A high resolution planar DMS device is often operated using a carrier gas flow rate of 2 to 4 L min −1 with dispersion voltages of 4 to 5 kV, 19,39,40 depending on the gas composition, flow rate and electrode gap width. Considering these factors, three combinations of carrier gas flow rates and dispersion voltages were simulated for a conventional DMS-capillary instrument.…”

“…For example, high resolution DMS can separate diastereomers, 12,13 isomeric perfluoroalkyl substances, 14 disaccharide epimers, 15 peptide isomers, 16,17 isomeric lipids, 18 and protein ion protonation isomers with the same mass, charge and collision cross section. 19 Moreover, resolving power values as high as ∼500 have been reported for high resolution DMS. 20…”

Protonation‐Induced Chirality Drives Separation by Differential Ion Mobility Spectrometry

“…[28][29][30][31] We then hypothesized that the separation was caused by protonation at differing gas-phase basic sites (i.e., prototropic isomers), which have been resolved by DMS in the past. [32][33][34][35] In the case of Verapamil, the energies of the prototropic isomers were significantly higher in energy relative to the isomers that were protonated at the tertiary amine (> 110 kJ mol À 1 ; Figure S3). Even if kinetic trapping was occurring, it is unlikely that these highenergy species would be present in the gas-phase ensemble.…”