A Mass-Selective Variable-Temperature Drift Tube Ion Mobility-Mass Spectrometer for Temperature Dependent Ion Mobility Studies

Abstract

A hybrid ion mobility-mass spectrometer (IM-MS) incorporating a variable-temperature (80-400 K) drift tube is presented. The instrument utilizes an electron ionization (EI) source for fundamental small molecule studies. Ions are transferred to the IM-MS analyzer stages through a quadrupole, which can operate in either broad transmission or mass-selective mode. Ion beam modulation for the ion mobility experiment is accomplished by an electronic shutter gate. The variable-temperature ion mobility spectrometer consists of a 30.2 cm uniform field drift tube enclosed within a thermal envelope. Subambient temperatures down to 80 K are achievable through cryogenic cooling with liquid nitrogen, while elevated temperatures can be accessed through resistive heating of the envelope. Mobility separated ions are mass analyzed by an orthogonal time-of-flight (TOF) mass spectrometer. This report describes the technological considerations for operating the instrument at variable temperature, and preliminary results are presented for IM-MS analysis of several small mass ions. Specifically, mobility separations of benzene fragment ions generated by EI are used to illustrate significantly improved (greater than 50%) ion mobility resolution at low temperatures resulting from decreased diffusional broadening. Preliminary results on the separation of long-lived electronic states of Ti + formed by EI of TiCl 4 and hydration reactions of Ti + with residual water are presented.

Recommendations for reporting ion mobility Mass Spectrometry measurements

“…For DT data, the buffer gas temperature is at present not included in the notation. Most measurements are performed in ambient conditions, that is, usually between 293 and 300 K. If temperature‐variable instruments (von Helden, Wyttenbach, & Bowers, ; Dugourd et al, ; Mao et al, ; Wyttenbach, Kemper, & Bowers, ; May & Russell, ; Ujma et al, ) become more widespread, or if measurement uncertainty becomes small enough that the exact temperature matters and the notion of “ambient conditions” is no longer sufficient, then introducing the temperature in the notation will become useful. This could come as an index next to the gas, for example: DT,1ry CCS He,298 .…”

Cryogenic Ion Mobility-Mass Spectrometry: Tracking Ion Structure from Solution to the Gas Phase

“…5 On the other hand, decreasing the temperature of the IM drift gas has been shown to reduce diffusional broadening of the ion swarm through the drift cell, resulting in increased sensitivity and resolution. 6 In addition, low temperatures are required for the preservation of hydrated analytes on the experimental time scale, because weakly bound clusters would otherwise dissociate rapidly. While hydrated biomolecules have predominantly been studied using spectroscopic methods or condensed-phase techniques, 7−9 recent gas-phase studies involving the sequential hydration of biomolecules have provided insights into the effect of hydration on ion structure.…”

Ion Mobility‐Mass Spectrometry

“…(33,34) Cryogenically cooled drift tubes with subambient temperatures have been recently demonstrated. (35) The ability to work with higher resolution drift instruments allows greater separation power for complex mixtures or isomeric and isobaric species with closely related mobilities and can give better insight into structural transitions in the gas phase.…”