Analysis of ionic liquid by field desorption (FD) ionization using JMS-T100GC “AccuTOF GC”

Importance of the Topic

Ionic liquids, composed entirely of ions or ion pairs, combine unique properties such as electrical conductivity, negligible vapor pressure, low combustibility and excellent thermal stability. These features position them as promising functional materials in applications ranging from green solvents to electrochemical devices.

Objectives and Study Overview

The aim of this work was to demonstrate the capability of field desorption (FD) ionization coupled with high-resolution time-of-flight mass spectrometry (JMS-T100GC “AccuTOF GC”) for characterizing a model ionic liquid. Specifically, the study sought to identify both the cationic and anionic components of 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide through accurate mass measurements.

Methodology

• Sample: 1-Butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide (Aldrich).
• Ionization: Field desorption in positive mode (FD(+)), cathode potential –10 kV, emitter current ramped to 35 mA.
• Mass range: m/z 35–800, with spectral acquisition every 1 s.

Used Instrumentation

• Mass spectrometer: JEOL JMS-T100GC “AccuTOF GC” high-resolution time-of-flight MS.

Main Results and Discussion

The FD mass spectrum exhibited a base peak at m/z 150.1, corresponding to the intact pyridinium cation (C10H16N)+. A secondary peak at m/z 580.2 was assigned to a cluster ion comprising one anion and two cation units. Accurate mass measurements yielded:

• Cation (C): measured m/z 150.1289 (calculated 150.1283), formula C10H16N.
• Cluster (CA+C): measured m/z 580.1766 (calculated 580.1738), formula C22H32F6N3O4S2.

By subtracting two cation units from the cluster ion, the anion composition was deduced as C2F6NO4S2. This approach highlights FD’s strength in preserving intact ions and revealing anion masses via cluster species.

Benefits and Practical Applications

• Minimal fragmentation allows direct detection of intact cations.
• High mass accuracy facilitates unambiguous elemental composition assignments for both ions.
• Applicable to quality control and structure confirmation of novel ionic liquids in research and industry.

Future Trends and Applications

• Integration with chromatographic separation for complex mixtures.
• Automation of FD probe handling for high-throughput screening.
• Extension to diverse ionic liquid chemistries and co-solvent systems.
• Combination with tandem MS for deeper structural elucidation.

Conclusion

Field desorption coupled with high-resolution TOF-MS provides a robust method for analyzing ionic liquids. The technique yields accurate masses of intact cations and cluster ions, enabling determination of both cationic and anionic compositions without extensive fragmentation.

Reference

1. J. H. Gross, Mass Spectrometry, Springer-Verlag Berlin Heidelberg, Germany (2004).
2. J. H. Gross, J. Am. Soc. Mass Spectrom., 18, 2254 (2007).