The solvent used in infrared spectrophotometry must not affect the cell, which usually consists of a halide salt such as sodium chloride or potassium bromide. Where possible, spectral grade solvents should be used.
No solvent is completely transparent throughout the entire infrared spectrum. Carbon tetrachloride R1 is practically transparent (up to 1 mm of thickness) over the range 4000-1700 cm-1 (2.5-5.9 µm). Dichloromethane R and dibromomethane R are useful solvents. Carbon disulfide IR2 (up to 1 mm in thickness) is suitable as a solvent up to 250 cm-1 (40 µm) except in the 2400-2000 cm-1 (4.2-5 µm) and the 1800-1300 cm-1 (5.6-7.7 µm) regions, where it has strong absorption. Its weak absorption in the 875-845 cm-1 (11.4-11.8 (µm) region should be noted. Other solvents have relatively narrow regions of transparency.
1 R: of reagent-grade quality.
2 IR: of suitable purity for use in spectrophotometry in the infrared region.