Abstract

An understanding of the species that form in mixtures of alcohol and water is important for their use in liquid chromatography applications. In reverse-phase liquid chromatography the retention of solutes on a chromatography column is influenced by the composition of the mobile phase, and in the case of alcohol and water mobile phases, the amount of free alcohol and water present. Previous and similar modeling studies of methanol (MeOH) and water mixtures by near-infrared (NIR) spectroscopy have found up to four species present including free MeOH and water and MeOH and water complexes formed by hydrogen bonding associations. In this work an equilibrium model has been applied to NIR measurements of MeOH and water mixtures. A high-performance liquid chromatography (HPLC) pump was coupled to an NIR flow cell to produce a gradual change in mixture composition. This resulted in a greater mixture resolution than has been achieved previously by manual mixture preparation. It was determined that five species contributed to the data. An equilibria model consisting of MeOH, H₂O, MeOH(H₂O) (log K_H2O^MeOH = 0.10 ± 0.03), MeOH(H₂O)₄ (log K_4H2O^MeOH = −2.14 ± 0.08), and MeOH(H₂O)₉ (log K_9H2O^MeOH = −8.6 ± 0.1) was successfully fitted to the data. The model supports the results of previous work and highlights the progressive formation of MeOH and water complexes that occur with changing mixture composition. The model also supports that mixtures of MeOH and water are not simple binary mixtures and that this is responsible for observed deviations from expected elution behavior.

Terahertz sensing of highly absorptive water-methanol mixtures with multiple resonances in metamaterials

Min Chen, Leena Singh, Ningning Xu, Ranjan Singh, Weili Zhang, and Lijuan Xie
Opt. Express 25(13) 14089-14097 (2017)

Rapid, accurate, and precise concentration measurements of a methanol–water mixture using Raman spectroscopy

Daniel D. Hickstein, Russell Goldfarbmuren, Jack Darrah, Luke Erickson, and Laura A. Johnson
OSA Continuum 1(3) 1097-1110 (2018)

Model for Infrared Emission of Water Vapor/Aerosol Mixtures

H. R. Carlon
Appl. Opt. 10(10) 2297-2303 (1971)

Determination of 1-propanol, ethanol, and methanol concentrations in water based on a one-dimensional phoxonic crystal sensor

Samar M. Shaban, Ahmed Mehaney, and Arafa H. Aly
Appl. Opt. 59(13) 3878-3885 (2020)

The Infrared Absorption Spectra of Mixtures of Alcohol and Water

Dudley Williams, R. D. Weatherford, and E. K. Plyler
J. Opt. Soc. Am. 26(4) 149-152 (1936)