The alkali halide disk technique in infra-red spectrometry : Anomalous behaviour of some samples dispersed in alkali halide disks

Abstract

Some difficulties encountered in the application of the alkali halide disk technique in infra-red spectrometry are discussed. Complications due to interaction of the sample with the alkali halide have been studied experimentally. It was found that the anomalous behaviour of benzoic acid, succinic acid, adipic acid and suocinimide in KBr and KCl disks must be ascribed to adsorption of the molecules of the sample on the surface of the alkali halide particles. The anomalous behaviour of α-naphthylacetamide, however, is caused by polymorphism of this substance, whereas the unusual spectrum of succinimide in KI disks is due to the formation of an addition product. The anomalies caused by adsorption can be eliminated by storage of the disks in a moist atmosphere; this “ageing process” is primarily caused by recrystallization of the alkali halide under the influence of water from the surrounding atmosphere.