A First Principle Model of Differential Ion Mobility: the Effect of Ion-Solvent Clustering

  • Alexander Haack
  • Jeff Crouse
  • Femke-Jutta Schlüter
  • Thorsten BenterEmail author
  • W. Scott HopkinsEmail author
Research Article


The use of differential mobility spectrometry (DMS) as a separation tool prior to mass analysis has increased in popularity over the years. However, the fundamental principles behind the difference between high- and low-field mobility is still a matter of debate—especially regarding the strong impact of solvent molecules added to the gas phase in chemically modified DMS environments. In this contribution, we aim to present a thorough model for the determination of the ion mobility over a wide range of field strengths and subsequent calculation of DMS dispersion plots. Our model relies on first principle calculations only, incorporating the modeling of the “hard-sphere” mobility, the change in CCS with field strength, and the degree of clustering of solvent molecules to the ion. We show that all three factors have to be taken into account to qualitatively predict dispersion plots. In particular, type A behavior (i.e., strong clustering) in DMS can only be explained by a significant change of the mean cluster size with field strengths. The fact that our model correctly predicts trends between differently strong binding solvents, as well as the solvent concentration and the background gas temperature, highlights the importance of clustering for differential mobility.


DMS Dispersion plot Ion mobility Collision cross section Population distribution 



We gratefully acknowledge the high-performance computing support from the SHARCNET consortium of Compute Canada. We also want to acknowledge Christian Ieritano for his help with the basin hopping algorithm.

Supplementary material

13361_2019_2340_MOESM1_ESM.pdf (904 kb)
ESM 1 (PDF 903 kb)


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Copyright information

© American Society for Mass Spectrometry 2019

Authors and Affiliations

  1. 1.Department of Physical and Theoretical ChemistryUniversity of WuppertalWuppertalGermany
  2. 2.Department of ChemistryUniversity of WaterlooWaterlooCanada

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