Abstract

Dissolution of electrolytes causes characteristic changes in the near-IR spectrum of water. These changes result from a decrease in the concentration of water; charge-dipole interactions between ions and water molecules; formation of hydrogen bonds between oxygen or nitrogen atoms in some ions and water molecules; production of H⁺ and OH^- ions from dissociation and hydrolysis; absorptions due to OH, NH, and CH groups in some ions; and intrinsic colors of some transition metal ions. Changes in spectra were used for identification of electrolytes in aqueous solutions. Near-IR spectra of 71 solutions of single electrolytes were measured and used to develop a spectral library. This near-IR spectral library was processed with principal component regression (PCR) and used for the identification of single and multiple electrolytes in aqueous solutions with the use of their spectra. Most of the unknown electrolytes were identified correctly. For the others, very similar electrolytes were selected with one ion identified correctly. The near-IR spectral library of aqueous solutions of electrolytes can be used as a simple and fast approach for the identification of electrolytes.

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