Remote measurements of concentration of organic solvents in binary mixtures using Raman spectroscopy

Abstract

Binary mixtures of methanol, ethanol, isoamyl alcohol, and acetic acid with water in various ratios have been studied using Raman spectroscopy. Upon variations in organic solvent concentration, the intensities of stretching vibration bands of CH and OH group change within the spectral range 2600–3800 cm−1. For quantitative characterization of the partial concentrations of a solvent, we have chosen the integral intensity ICH of CH group stretching vibrations normalized to the total intensity of bands of CH and OH groups (ICH + IOH) within the 2600–3800 cm−1 range. With this normalization, the intensity ICH/(ICH + IOH) linearly depends on the volume fraction of the organic solvent throughout the whole range of its concentrations for the spectra of all mixtures. This allows noncontact measurements of concentrations of organic solvents in water solutions, including flammable or toxic ones. The relative concentration accuracy is 0.5, 1.1, and 1.5% for aqueous ethanol, methanol, and acetic acid, respectively.