Determination of water in acetonitrile, propionitrile, dimethylformamide and tetrahydrofuran by infrared and near-infrared spectrometry

Abstract

For determining small amounts of water in non-aqueous solvents (acetonitrile, propionitrile, dimethylformamide and tetrahydrofuran) IR and near-IR spectrometry were applied. In order to prevent overlapping of the observed water band with that of the solvent, either one of the fundamental vibrations (v₁ or v₃ at about 3500 cm^–1) was selected or combination vibrations (v₁+v₂) at 5200 cm^–1. This method is rapid and convenient, especially in laboratories that are not equipped with a single-purpose analytical titrator according to Karl Fischer, or where water is not often determined. The detection limit is about 20 p.p.m. of water, i.e., 10^–3 mol l^–1. Further uses of the method were verified experimentally and are discussed.