Chemical Analysis of Ionic Liquids Using Photoelectron Spectroscopy

The feasibility of utilizing X‐ray photoelectron spectroscopy (XPS) to analyze room‐temperature ionic liquids (RTILs) was investigated in this study. Conventionally, the chemical structure of organic compounds is identified by nuclear magnetic resonance (NMR) spectroscopy. The properties of RTILs, especially their low vapor pressure, make it possible to analyze RTILs by using XPS. The usefulness of XPS on RTILs was confirmed by commercial RTILs. All atoms in RTILs were detected in survey XPS spectra, and the calculated atomic percentages matched well with theoretical values. After the verification of commercial RTILs by XPS, we synthesized three RTILs and investigated them with XPS. The atomic ratio and chemical environment of carbon in RTILs were verified by XPS. By adapting XPS to the investigation of RTILs, carbon atoms in different chemical environments were distinguishable by the binding energy shift, and the atomic ratio of the constituent atoms was identifiable after peak deconvolution. In addition, inorganic constituents were detected by XPS unlike in the case of NMR spectroscopy.