Ionic Liquids in Chemical Analysis

Abstract

Room-temperature ionic liquids are salts with a melting point close to or below room temperature. They form liquids composed in the majority of ions. This gives these materials the potential to behave very differently when they are used as solvents compared to conventional molecular liquids. The search for their application is growing in every area of analytical chemistry—electrochemistry, chromatography, electrophoresis, and even mass spectrometry. The literature on ionic liquids is growing almost exponentially. The basis for this activity is the easy preparation of salts with different ion constituents. This ability might best be described as the “chemical tunability” of ionic liquids, a class of solvents with members possessing similar physical properties but having different chemical behavior. Their good solvating properties, together with large spectral transparency, make ionic liquids suitable solvents for spectroscopic measurements. It has been demonstrated that task-specific ionic liquids have advantages compared to common solvents used as separation media in liquid-liquid extraction processes achieving high efficiencies and selectivities of separation. The main advantage for other applications of ionic liquids in analytical chemistry lies in their low volatility which makes them useful as solvents for working in both high-temperature (gas chromatography (GC) stationary phases) and high-vacuum (MALDI matrixes) environments. When using an ionic liquid as an electrolyte medium, it is possible to achieve a broader range of operational temperatures and conditions relative to other conventional electrolytic media, and this makes ionic liquids promising materials in various electrochemical devices (e.g., batteries, fuel cells, sensors, and electrochromic windows).