Puxty Graeme, Maeder Marcel, Radack Kyle P, Gemperline Paul J
Department of Chemistry, University of Newcastle, NSW, Australia.
Appl Spectrosc. 2005 Mar;59(3):329-34. doi: 10.1366/0003702053585444.
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(MeOH)H2O = 0.10+/-0.03), MeOH(H2O)4 (log K(MeOH)4H2O = -2.14+/-0.08), and MeOH(H2O)9 (log K(MeOH)9H2O = -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.
了解酒精和水混合物中形成的物种对于它们在液相色谱应用中的使用非常重要。在反相液相色谱中，溶质在色谱柱上的保留受流动相组成的影响，对于酒精和水流动相而言，还受游离酒精和水的含量影响。此前对甲醇（MeOH）和水混合物进行的类似近红外（NIR）光谱建模研究发现，存在多达四种物种，包括游离的MeOH和水以及通过氢键缔合形成的MeOH和水络合物。在这项工作中，一个平衡模型被应用于MeOH和水混合物的近红外测量。一台高效液相色谱（HPLC）泵与一个近红外流通池相连，以产生混合物组成的逐渐变化。这导致混合物分辨率比之前通过手动制备混合物所达到的更高。确定有五种物种对数据有贡献。一个由MeOH、H2O、MeOH(H2O)（log K(MeOH)H2O = 0.10±0.03）、MeOH(H2O)4（log K(MeOH)4H2O = -2.14±0.08）和MeOH(H2O)9（log K(MeOH)9H2O = -8.6±0.1）组成的平衡模型成功拟合了数据。该模型支持了之前工作的结果，并突出了随着混合物组成变化而逐渐形成的MeOH和水络合物。该模型还支持MeOH和水的混合物不是简单的二元混合物，这也是观察到的与预期洗脱行为偏差的原因。
