Fundamentals of ion mobility spectrometry

Abstract

Fundamental questions in ion mobility spectrometry have practical implications for analytical applications in general, and omics in particular, in three respects. (1) Understanding how ion mobility and collision cross section values depend on the collision gas, on the electric field and on temperature is crucial to ascertain their transferability across instrumental platforms. (2) Predicting collision cross section values for new analytes is necessary to exploit the full potential of ion mobility in discovery workflows. (3) Finally, understanding the fate of ion structures in the gas phase is essential to infer meaningful information on solution structures based on gas-phase ion mobility measurements. We review here the most recent advances in ion mobility fundamentals, relevant to these three aspects.

Recommendations for reporting ion mobility Mass Spectrometry measurements

“…The E / N values for drift tube typically vary from 1 to 15 Td (1 Td = 10 –21 V m 2 ). –TWIMS (traveling wave ion mobility spectrometry), in which ions are directed through a stationary gas by a sequence of symmetric potential waves continually propagating through the drift region (Giles et al, ). The ions are subjected to varying E / N , with peak values reaching 50–160 Td (Giles et al, ; Gabelica & Marklund, ). Structures for lossless ion manipulation (SLIM) can be used to implement traveling waves (Tolmachev et al, ) and thus perform TWIMS separations (Deng et al, ; Ibrahim et al, ). –TIMS (trapped ion mobility spectrometry), in which ions are held in place against a moving gas with an electric field (Fernandez‐Lima et al, ).…”

“…Multiple isomers/conformers are trapped simultaneously at different E values resulting from a voltage gradient applied across the IMS tunnel region. The typical E / N is 45–85 Td (Gabelica & Marklund, ). Ions are then released by decreasing the electric field in steps.…”

“…It is also desirable to have an explicit notation for values obtained by the primary method, versus secondary or empirical methods. As discussed elsewhere (Gabelica & Marklund, ), the range of fields used in so‐called linear methods can differ enough so that effective temperatures higher than the gas temperature may be reached in TWIMS, TIMS, or in DTIMS at high fields. Further, K 0 and CCS depend on the population distribution of ion structures sampled in the experiment, which can be different for different experimental setups.…”

“…In the future, the calibration method may be generalized to explicitly account for velocity relaxation (Richardson, Langridge, & Giles, ). Further, using DT CCS He values to calibrate TWIMS instrument working mainly in nitrogen (which was frequent in the early days, as often only DT CCS He values were available) adds other compound‐class effects (Gabelica & Marklund, ) related to the interaction potentials of nitrogen and helium with the exposed surface groups (Bleiholder et al, ). Here, the charge density will play the largest role (Young & Bleiholder, ), and for multiply charged proteins these effects become significant (Canzani, Laszlo, & Bush, ) compared with measurement precision.…”

DNA adducts: Formation, biological effects, and new biospecimens for mass spectrometric measurements in humans

“…Ion mobility spectrometry (IMS) separates gas‐phase ions based on the differences in the mobility of molecules drifting through a buffer gas under an electric field. It is available in different configurations in many commercial MS instruments and has been widely used in basic science, pharmaceutical industry, forensic science, etc . As a proof of concept, Kafle and co‐workers reported the application of IMS in the detection and quantification of N ‐(2′‐deoxyguanosin‐8‐yl)‐4‐ABP (dG‐C8‐4‐ABP) in 4‐ABP‐modified calf thymus DNA .…”