ATR and transmission IR spectroscopy have been used to investigate the state of water in room temperature ionic liquids (RTILs) based on the 1-alkyl-3-methylimidazolium cation with the anions: [PF₆]⁻, [SbF₆]⁻, [BF₄]⁻, [ClO₄]⁻, [CF₃SO₃]⁻, [(CF₃SO₂)₂N]⁻, [NO₃]⁻ and [CF₃CO₂]⁻. It has been shown that in these RTILs water molecules absorbed from the air are present mostly in the “free” (not self-associated) state, bound via H-bonding with [PF₆]⁻, [BF₄]⁻, [SbF₆]⁻, [ClO₄]⁻, [CF₃SO₃]⁻, [(CF₃SO₂)₂N]⁻ with the concentrations of dissolved water in the range 0.2–1.0 mol dm⁻³. It has been concluded that most of the water molecules at these concentrations exist in symmetric 1 : 2 type H-bonded complexes: anion...HOH...anion. Additional evidence that the preferred sites of interaction with water molecules are the anions has been obtained from the experiments with RTILs of the 1-butyl-2,3-dimethylimidazolium and 1-butyl-2,3,4,5-tetramethylimidazolium cations. Water molecules can also form associated liquid-like formations in RTILs with anions of stronger basicity such as [NO₃]⁻ and [CF₃CO₂]⁻. When these RTILs are exposed to air the water concentrations exceed 1.0 mol dm⁻³. The strength of H-bonding between water molecules and anions increases in the order [PF₆]⁻ < [SbF₆]⁻ < [BF₄]⁻ < [(CF₃SO₂)₂N]⁻ < [ClO₄]⁻ < [CF₃SO₃]⁻ < [NO₃]⁻ < [CF₃CO₂]⁻. The energies of this H-bonding were estimated from spectral shifts, with the resulting enthalpies being in the range 8–13 kJ mol⁻¹. ATR-IR spectroscopy has also been used to study H-bonding between methanol and RTILs.

An in situ ATR (attenuated total reflectance)-IR study of CO₂ dissolved in two ionic liquids at high pressures has demonstrated the effects of the anionic species of the ionic liquids on the molecular state of the dissolved CO₂.

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging is a highly versatile, label free and non-destructive chemical imaging method which can be applied to study a wide range of samples and systems. This review summarises some of the recent advances and applications of this imaging method in the area of biomedical studies, including examples of section of aorta, skin tissue and live cells. Two of the major advantages of measuring in ATR mode are the opportunity to measure samples that absorb strongly in the IR spectrum, such as aqueous systems, without significant sample preparation and the ability to increase the spatial resolution of the measured image. The implications of these advantages as well as some limitations of this imaging approach are discussed and a brief outlook at some of the possible future developments in this area is provided.