Toward Screening for Aromatic N-Heterocycle-Based Ionic Liquid Species in Solution by Mass Spectrometry

The synthesis and use of ionic liquids (ILs) has increased since their inception, driven by their properties and tunability, and it follows that concerns have grown about potential environmental release and persistence. There is thus a motivation to develop and improve methods for the analysis of IL species. However, focus on the detection and characterization of IL species from dilute solutions, rather than the characterization of their bulk properties, is still lacking. The goal of this work is to (1) explore whether DART-MS might be a useful tool to pursue for rapid detection of known ionic liquid species from solution, (2) introduce class-based diagnostic product ions for common aromatic N-heterocyclic ionic liquid cations, and (3) demonstrate the m/z 83 ion as an example of such a diagnostic marker for methyl-imidazolium-based IL cations. The results demonstrated that DART-MS allows for the observation of intact IL cations from dilute solutions of ILs and is thus promising for rapid detection of IL species from solution, although additional steps such as preconcentration may be necessary for many environmentally relevant concentrations. Furthermore, in-source CID screening for the m/z 83 characteristic product ion for methyl-imidazolium-based IL cations was demonstrated in proof-of-principle examples, showing promise for future method development. While the initial motivation for this work was the dearth of methods exploration for environmental contamination detection, these results are also broadly applicable to other cases where detection and characterization of IL species are needed and provide initial results upon which further method development can build for specific applications.