Soukup Jan, Jandera Pavel
Department of Analytical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, CZ 53210 Pardubice, Czech Republic.
Department of Analytical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, CZ 53210 Pardubice, Czech Republic.
J Chromatogr A. 2014 Dec 29;1374:102-111. doi: 10.1016/j.chroma.2014.11.028. Epub 2014 Nov 18.
Excess adsorption of water from aqueous acetonitrile mobile phases was investigated on 16 stationary phases using the frontal analysis method and coulometric Karl-Fischer titration. The stationary phases include silica gel and silica-bonded phases with different polarities, octadecyl and cholesterol, phenyl, nitrile, pentafluorophenylpropyl, diol and zwitterionic sulfobetaine and phosphorylcholine ligands bonded on silica, hybrid organic-silica and hydrosilated matrices. Both fully porous and core-shell column types were included. Preferential uptake of water by the columns can be described by Langmuir isotherms. Even though a diffuse rather than a compact adsorbed discrete layer of water on the adsorbent surface can be formed because of the unlimited miscibility of water with acetonitrile, for convenience, the preferentially adsorbed water was expressed in terms of a hypothetical monomolecular water layer equivalent in the inner pores. The uptake of water strongly depends on the polarity and type of the column. Less than one monomolecular water layer equivalent was adsorbed on moderate polar silica hydride-based stationary phases, Ascentis Express F5 and Ascentis Express CN column at the saturation capacity, while on more polar stationary phases, several water layer equivalents were up-taken from the mobile phase. The strongest affinity to water was observed on the ZIC cHILIC stationary phases, where more than nine water layer equivalents were adsorbed onto its surface at its saturation capacity. Columns with bonded hydroxyl and diol ligands show stronger water adsorption in comparison to bare silica. Columns based on hydrosilated silica generally show significantly decreased water uptake in comparison to stationary phases bonded on ordinary silica. Significant correlations were found between the water uptake and the separation selectivity for compounds with strong polarity differences.
使用前沿分析法和库仑卡尔费休滴定法，在16种固定相上研究了从乙腈水流动相中过量吸附水的情况。固定相包括硅胶和具有不同极性的硅胶键合相、键合在硅胶上的十八烷基和胆固醇、苯基、腈基、五氟苯基丙基、二醇以及两性离子磺基甜菜碱和磷酰胆碱配体、杂化有机硅胶和硅氢化基质。研究中纳入了全多孔和核壳两种柱型。柱对水的优先吸附可用朗缪尔等温线描述。尽管由于水与乙腈无限混溶，在吸附剂表面可能形成的是扩散而非紧密吸附的离散水层，但为方便起见，优先吸附的水仍以孔内假想单分子水层当量来表示。水的吸附量强烈依赖于柱的极性和类型。在饱和容量下，中等极性的硅胶氢化物基固定相Ascentis Express F5和Ascentis Express CN柱上吸附的水当量少于一个单分子水层，而在极性更强的固定相上，从流动相中吸附了几个水层当量。在ZIC cHILIC固定相上观察到对水的亲和力最强，在其饱和容量下，其表面吸附了九个以上的水层当量。与裸硅胶相比，键合有羟基和二醇配体的柱表现出更强的水吸附。与普通硅胶键合的固定相相比，基于硅氢化硅胶的柱通常显示出显著降低的水吸附量。对于极性差异较大的化合物，发现水吸附量与分离选择性之间存在显著相关性。
