Detection of Hydrate Forms of Lithium and Sodium Perchlorates in Aqueous Solutions Using near Infrared Spectroscopy

Abstract

A new approach to the study of concentrated electrolyte water solutions is proposed. NIR spectra of aqueous solutions of LiClO4 and NaClO4 were studied. The pure spectra and concentration profiles of spectral forms in the solutions were found by deconvolution of an experimentally measured data matrix. The chemometric analysis and the generalised phenomenological model of the structure of aqueous electrolyte solutions were used to establish that the variation in spectra of LiClO4 solutions with concentration is due to antibatic changes in the fractions of water that is unbonded with ions and of water in the structure of the cybotactic group of lithium perchlorate trihydrate. Corresponding changes in NaClO4 solutions are also associated with interconversion of sodium perchlorate forms of di- and monohydrates. Hydrate forms of lithium and sodium perchlorates in aqueous solutions are described, and a cybotactic group in a saturated solution is found to be equivalent to a solid-phase structure fragment. A strategy for selecting the nature of a background electrolyte is recommended.