Electric field dependence of the ion mobility

The dependence of mobility on electric field (the alpha function in differential mobility spectrometry, DMS) is a unique ion property used for separation and characterization of gas-phase ions in DMS. This study was conducted to determine the origin of this field dependence. Several models are suggested to rationalize the field mobility dependence and explain the alpha function behavior under typical experimental conditions. Alpha function properties, calculated in the framework of each model, are compared with experimental data. Qualitative and quantitative correlations between theory and experiment are analyzed as a proof of the validity of each model. Our examination reveals that clustering with dopant and drift gas molecules is the most relevant hypothesis explaining the observed phenomena. A clustering model can serve as a basis for further investigations aimed at significantly increasing DMS resolution by drift gas modification. (C) 2009 Elsevier B.V. All rights reserved.