Australian Centre for Research on Separation Science (ACROSS), School of Chemistry, Monash University, Melbourne, Victoria 3800, Australia.
Department of Chemistry, San Jose State University, San Jose, CA 95192, USA.
Anal Chim Acta. 2016 Apr 15;916:102-11. doi: 10.1016/j.aca.2016.02.013. Epub 2016 Feb 20.
In this study, the surface charge properties of perfluorinated C8 (PerfluoroC8) and undecanoic acid (UDA) modified silica hydride stationary phases have been investigated. The zeta potential values of these stationary phases were measured in aqueous/acetonitrile mobile phases of different pH, buffer concentrations and acetonitrile contents. The retention behaviour of several basic, acidic and neutral compounds were then examined with these two stationary phases, with U-shaped retention dependencies evident with regard to the organic solvent content of the mobile phase. Plots of the logarithmic retention factor versus buffer concentration revealed slopes ≥ -0.41 for both stationary phases, indicating the involvement of mixed mode retention mechanisms with contributions from both ionic and non-ionic interactions. Using a linear solvation energy relationship approach, the origins of these interactions under different mobile phase conditions were differentiated and quantified. The PerfluoroC8 stationary phase exhibited stronger retention for basic compounds under high acetonitrile content mobile phase conditions, whilst stronger retention was observed for all compounds with the UDA stationary phase under high aqueous content mobile phase conditions. The more negative zeta potentials of the UDA stationary phase correlated with higher total charge density, surface charge density and charge density at the beta plane (the outer plane of the double layer) compared to the PerfluoroC8 stationary phase. With mobile phases of low buffer concentrations, more negative zeta potential values were unexpectedly observed for the PerfluoroC8 stationary phase with slight increases in the C descriptor value, reflecting also the greater accessibility of the analytes to the stationary phase surface. Comparison of the retention behaviours on these phases with other types of silica hydride stationary phases has revealed different patterns of selectivity.
在这项研究中，研究了全氟辛基（PerfluoroC8）和十一烷酸（UDA）修饰的硅氢化物固定相的表面电荷特性。在不同 pH 值、缓冲浓度和乙腈含量的水/乙腈流动相中测量了这些固定相的动电位值。然后，使用这两种固定相研究了几种碱性、酸性和中性化合物的保留行为，对于流动相中的有机溶剂含量，呈现出 U 形保留依赖性。以缓冲浓度为对数保留因子作图，对于两种固定相，斜率均≥-0.41，表明存在混合模式保留机制，其中包括离子和非离子相互作用的贡献。使用线性溶剂化能关系方法，区分并量化了不同流动相条件下这些相互作用的起源。在高乙腈含量的流动相条件下，全氟辛基固定相对碱性化合物表现出更强的保留，而在高含水量的流动相条件下，UDA 固定相对所有化合物表现出更强的保留。与全氟辛基固定相相比，UDA 固定相的动电位更负，这与更高的总电荷密度、表面电荷密度和β平面（双层的外层）上的电荷密度相关。对于缓冲浓度低的流动相，出乎意料的是，全氟辛基固定相的动电位值更负，而 C 描述符值略有增加，这也反映了分析物更接近固定相表面。与其他类型的硅氢化物固定相的保留行为比较表明，存在不同的选择性模式。
