Raman spectroscopy was used to study the NaCl aqueous solutions around the solid–liquid phase transition. Special attention was devoted to the modification induced by the salt on the OH stretching band of water. Investigations were carried out in the temperature range between −21 and 10 °C, for concentrations from 0 to 200 g/L. We demonstrated that micro-Raman spectroscopy can be used as a marker, allowing the determination of the salt concentration of an aqueous solution with an error close to ±5%.
Ivana Đuričković, Mario Marchetti, Rémy Claverie, Patrice Bourson, Jean-Marie Chassot, and Marc D. Fontana, "Experimental Study of NaCl Aqueous Solutions by Raman Spectroscopy: Towards a New Optical Sensor," Appl. Spectrosc. 64, 853-857 (2010)