Application of Two-dimensional Covariance Analysisto Infrared Spectroscopic Studies of Electrolyte Solutions

Abstract

Two-dimensional correlation analysis is applied, for the first time, to aid in structural studies of electrolyte solutions. Concentration dependent spectral features due to solute–solvent and solute–solute interactions can be separated from each other and their relative correlated changes established. The application of 2D correlation analysis, using a generalized covariance approach, is demonstrated using FTIR–ATR data for sub-molar concentrations of lithium perchlorate in diethyl ether. Although it has been established that, as the electrolyte salt concentration increases, the concentration of diethyl ether in the trans–trans conformation decreases relative to diethyl ether in the trans–gauche conformation, no evidence of these changes could be seen in the methyl and methylene C–H stretching bands. This region of the mid-IR spectra was previously thought to show no solute–solvent dependent bands. The 2D covariance analysis performed in this study shows clearly that methyl and methylene stretching modes can be associated uniquely with either the trans–trans or the trans–gauche conformer.