Chemical Effects in the Separation Process of a Differential Mobility/Mass Spectrometer System

Abstract

In differential mobility spectrometry (DMS, also referred to as high field asymmetric waveform ion mobility spectrometry, FAIMS), ions are separated on the basis of the difference in their mobility under high and low electric fields. The addition of polar modifiers to the gas transporting the ions through a DMS enhances the formation of clusters in a field-dependent way and thus amplifies the high and low field mobility difference resulting in increased peak capacity and separation power. Observations of the increase in mobility field dependence are consistent with a cluster formation model, also referred to as the dynamic cluster-decluster model. The uniqueness of chemical interactions that occur between an ion and cluster-forming neutrals increases the selectivity of the separation and the depression of low-field mobility relative to high-field mobility increases the compensation voltage and peak capacity. The effect of polar modifiers on the peak capacity across a broad range of chemicals has been investigated. We discuss the theoretical underpinnings which explain the observed effects. In contrast to the result from polar modifiers, we find that using mixtures of inert gases as the transport gas improve resolution by reducing peak width but has very little effect on peak capacity or selectivity. Inert gases do not cluster and thus do not reduce low field mobility relative to high-field mobility. The observed changes in the differential mobility α parameter exhibited by different classes of compounds when the transport gas contains polar modifiers or has a significant fraction of inert gas can be explained on the basis of the physical mechanisms involved in the separation processes.

Predicting Compensation Voltage for Singly-charged Ions in High-Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS)

“…It should be emphasized that the above considerations only apply when ions are properly desolvated [11]. As a troubleshooting aid, a discrepancy between predicted and experimental CV values may help to trace potential problems in experimental operation [4].…”

“…It was also shown with the use of buffer gas modifiers [11] that complexation plays a certain role in the order of emergence and resolution of ions within FAIMS systems. In general, reports of correlation of CV and m/z are scarce and sometimes conflicting.…”

Differential Mobility Spectrometry-Hydrogen Deuterium Exchange (DMS-HDX) as a Probe of Protein Conformation in Solution

“…In the planar DMS setup shown in Figure 1, a transport gas (typically N 2 ) containing the modifier gas mix is introduced at the DMS inlet [31,32]. A second 'throttle' gas can be introduced at the interface between the DMS and the mass spectrometer for resolution enhancement [3,28].…”

Improved Differential Ion Mobility Separations Using Linked Scans of Carrier Gas Composition and Compensation Field

“…The effective gap takes into account the oscillation amplitude of an ion during one period of the dispersion waveform. Ion mobility through a gas is affected by the masses, interactions, and cross-sections of the ions and gas molecules [23,24]. The introduction of helium as a carrier gas decreases both the reduced mass and the collisional cross-sections of the collision partners.…”

“…This can be particularly harmful during analyses in which the main goal is identification of unknown compounds [24]. Here we present Blinked scans,^a new DIMS method that dynamically decreases the percent helium present in the carrier gas as the compensation field is increased.…”