Application of Ion Mobility Spectrometry and the Derived Collision Cross Section in the Analysis of Environmental Organic Micropollutants

Abstract

Ion mobility spectrometry (IMS) is a rapid gas-phase separation technique, which can distinguish ions on the basis of their size, shape, and charge. The IMS-derived collision cross section (CCS) can serve as additional identification evidence for the screening of environmental organic micropollutants (OMPs). In this work, we summarize the published experimental CCS values of environmental OMPs, introduce the current CCS prediction tools, summarize the use of IMS and CCS in the analysis of environmental OMPs, and finally discussed the benefits of IMS and CCS in environmental analysis. An up-to-date CCS compendium for environmental contaminants was produced by combining CCS databases and data sets of particular types of environmental OMPs, including pesticides, drugs, mycotoxins, steroids, plastic additives, per- and polyfluoroalkyl substances (PFAS), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs), as well as their well-known transformation products. A total of 9407 experimental CCS values from 4170 OMPs were retrieved from 23 publications, which contain both drift tube CCS in nitrogen (^DTCCS_N2) and traveling wave CCS in nitrogen (^TWCCS_N2). A selection of publicly accessible and in-house CCS prediction tools were also investigated; the chemical space covered by the training set and the quality of CCS measurements seem to be vital factors affecting the CCS prediction accuracy. Then, the applications of IMS and the derived CCS in the screening of various OMPs were summarized, and the benefits of IMS and CCS, including increased peak capacity, the elimination of interfering ions, the separation of isomers, and the reduction of false positives and false negatives, were discussed in detail. With the improvement of the resolving power of IMS and enhancements of experimental CCS databases, the practicability of IMS in the analysis of environmental OMPs will continue to improve.

Keywords: collision cross section; environmental organic micropollutants; ion mobility; nontargeted analysis; suspect screening.

Figure 1

(A) Depiction of CCS values vs mass values for 9407 ions together with the distribution of CCS and m/z values. (B) Distribution of 4170 compounds across super classes.

Figure 2

Different types of CCS values (A) and their relative errors (B).

Figure 3

Distribution of relative standard deviations of the CCS data.

Figure 4

Comparison of HRMS spectra for benzoylecgonine from an analytical reference standard solution (a), DT-aligned data of positive finding in wastewater sample (b), and non-DT aligned data of the same positive finding in wastewater (c). Reprinted with permission from ref (21). Copyright 2020 American Chemical Society.

Figure 5

Arrival time distributions of the regioisomers aldrin and isodrin in charge transfer conditions (left) and proton transfer conditions (right). Reprinted with permission from ref (58). Copyright 2022 American Chemical Society (licensed under CC-BY 4.0, https://creativecommons.org/licenses/by/4.0/).