Damping Factor Links Periodic Focusing and Uniform Field Ion Mobility for Accurate Determination of Collision Cross Sections

The methodology for obtaining accurate ion-neutral collision cross section (Omega) values for peptides and proteins using periodic focusing ion mobility spectrometry (PF IMS) is presented. A mobility dampening factor (represented by the term alpha) is introduced to account for the relative increase in ion-neutral collisions in PF IMS compared to uniform field ion mobility spectrometry (UF IMS) for equivalent operating conditions. The results show that alpha may be easily quantified both theoretically and empirically for a specific PF IMS design operating at a given pressure based upon the charge state of the analyte. By simply incorporating an alpha term into traditional UF IMS expressions, accurate Omega values were obtained with excellent agreement (<= 4% difference) compared to UF IMS measurements found in the current literature.