Ion Mobility Shift of Isotopologues in a High Kinetic Energy Ion Mobility Spectrometer (HiKE-IMS) at Elevated Effective Temperatures

Abstract

Ion mobility spectrometers (IMS) separate ions mainly by ion-neutral collision cross section and to a lesser extent by ion mass and effective temperature. When investigating isotopologues, the difference in collision cross section can be assumed negligible. Since the mobility shift of isotopologues is thus mainly caused by their difference in mass and effective temperature the investigation of isotopologues can provide important insights into the theory of ion mobility. However, in classical IMS operated at ambient pressure, cluster formation with neutral molecules occurs, which significantly influences the mobility shift of isotopologues and thus makes a sound investigation of the effect of ion mass and effective temperature on the ion mobility difficult. In this work, the relative ion mobility of several organic compounds and their 13 C-labelled isotopologues is studied in a High Kinetic Energy Ion Mobility Spectrometer (HiKE-IMS) at high reduced electric fields up to 120 Td, which allows the investigation of non-clustered ion species and thus enables a sound investigation of the mobility shift of isotopologues. The results show that the measured relative ion mobilities of isotopologues having the same effective temperature, and thus their ion mass dominating the relative ion mobility, agree well with theoretical relative ion mobilities predicted by the theory of ion mobility.

Investigation of Zero-/High-Field Ion Mobility Orthogonal Separation Using a Hyphenated DMA–FAIMS System and Validation of the Two-Temperature Theory at Arbitrary Field for Tetraalkylammonium Salts in Nitrogen

“…Krylov et al created a fitting procedure for their experimental data based on an energy loss ratio . More recent experimental work by Schaefer et al focuses on high-field energy corrections using the Hike-IMS …”

“…We show that this instrument combination enables determination of the field-dependent mobilities of tetraalkylammonium ions, and in doing so, validating the advantages of coupling these orthogonal techniques to aid in the separation and identification process. Subsequently, with unique mobility versus E/n data (parameterized through known zero-field mobility FAIMS curves), we then verify two-temperature model predictions of field strength-dependent mobility in polyatomic gases, with calculations performed via IMoS. , This brings an important level of quantification to nonlinear mobility measurements, a topic of considerable recent interest. − …”

“…59 More recent experimental work by Schaefer et al focuses on high-field energy corrections using the Hike-IMS. 27 Inferring Field-Dependent Mobilities from data. With the information obtained through the dispersion curve, one could calculate the mobility at a non-negligible electric field by calculating the α coefficients.…”

Measurement and Theory of Gas-Phase Ion Mobility Shifts Resulting from Isotopomer Mass Distribution Changes

“…Based on eq it has been broadly assumed that isotopologues should separate due to their reduced mass differences given sufficiently high IMS resolving power R p . As anticipated, such separations have been observed in low ,, electric fields in addition to those observed in the high field regime. ,− Similarly, given eq , it has been assumed that mobility differences for isotopomers would be far too small or completely indistinguishable as their CCS would be indistinguishable from a theoretical perspective . However, the recently observed IMS isotopomer mobility shifts obtained from ultra-high-resolution SLIM IMS leads to the hypothesis that internal degrees of freedom, vibrational and rotational, must be a key element for such separation.…”

Plate‐height model of ion mobility‐mass spectrometry: Part 2—Peak‐to‐peak resolution and peak capacity

“…To study the effect of reduced mass difference on δ v independently of other influencing factors, Ω and z were assumed to be identical, the absolute values being irrelevant. Although kinetic theory [34,35] and some experiments [33] suggest that isotopologues may have extremely small differences in their Ω values, for practical purposes the assumption of identical Ω remains generally valid [36,37]. The two plots in Figure 2 depict δ v for analyte pairs with nonidentical masses as a function of their mean mass ⟨m ion ⟩.…”