Dai Jun, Yang Xiqin, Carr Peter W
Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455-0431, USA.
J Chromatogr A. 2003 Jul 11;1005(1-2):63-82. doi: 10.1016/s0021-9673(03)00929-4.
In this study, we compare the separation of basic drugs on several octadecyl silane bonded silica (ODS) phases and a polybutadiene-coated zirconia (PBD-ZrO2) phase. The retention characteristics were investigated in detail using a variety of cationic drugs as probe solutes. The ODS phases were selected to cover a relatively wide range in silanol activity and were studied with ammonium phosphate eluents at pH 3.0 and 6.0. Compared to any of the ODS phases, the PBD-ZrO2 phase showed very significant differences in selectivities towards these drugs. Due to the presence of both reversed-phase and ion-exchange interactions between the stationary phase and the basic analyte on ODS and PBD-ZrO2, mixed-mode retention takes place to some extent on both types of phases. However, very large differences in the relative contributions from ion-exchange and reversed-phase interactions on the two types of phases led to quite different selectivities. When phosphate is present in the eluent and adsorbs on the surface, the PBD-ZrO2 phase takes on a high negative charge over a wide pH range due to phosphate adsorption on its surface. On ODS phases, ion-exchange interactions result from the interactions between protonated basic compounds and ionized residual silanol groups. Since the pH of the eluent influences the charge state of the silanol groups, the ion-exchange interactions vary in strength depending on pH. At pH 6.0, the ion-exchange interactions are strong. However, at pH 3.0 the ion-exchange interactions on ODS are significantly smaller because the silanol groups are less dissociated at the lower pH. Thus, not only are the selectivities of the ODS and PBD-ZrO2 phases different but quite different trends in retention are observed on these two types of phases as the pH of the eluent is varied. More importantly, by using the large set of "real" basic analytes we show the extreme complexity of the chromatographic processes on the reversed stationary phases. Both the test condition and solute property influence the column performance. Therefore, use of only one or two probe solutes is not sufficient for column ranking.
在本研究中，我们比较了几种十八烷基硅烷键合硅胶（ODS）固定相和聚丁二烯涂层氧化锆（PBD-ZrO₂）固定相上碱性药物的分离情况。使用多种阳离子药物作为探针溶质详细研究了保留特性。选择ODS固定相以覆盖硅醇活性相对较宽的范围，并在pH 3.0和6.0的磷酸铵洗脱液中进行研究。与任何一种ODS固定相相比，PBD-ZrO₂固定相对这些药物的选择性表现出非常显著的差异。由于在ODS和PBD-ZrO₂固定相上，固定相与碱性分析物之间同时存在反相和离子交换相互作用，在这两种类型的固定相上都在一定程度上发生了混合模式保留。然而，两种类型固定相上离子交换和反相相互作用的相对贡献存在很大差异，导致选择性截然不同。当洗脱液中存在磷酸盐并吸附在表面时，由于磷酸盐在其表面的吸附，PBD-ZrO₂固定相在较宽的pH范围内呈现高负电荷。在ODS固定相上，离子交换相互作用源于质子化碱性化合物与离子化残留硅醇基团之间的相互作用。由于洗脱液的pH影响硅醇基团的电荷状态，离子交换相互作用的强度随pH而变化。在pH 6.0时，离子交换相互作用很强。然而，在pH 3.0时，ODS上的离子交换相互作用明显较小，因为在较低pH下硅醇基团的解离程度较低。因此，不仅ODS和PBD-ZrO₂固定相的选择性不同，而且随着洗脱液pH的变化，在这两种类型的固定相上观察到截然不同的保留趋势。更重要的是，通过使用大量“真实”的碱性分析物，我们展示了反相固定相上色谱过程的极端复杂性。测试条件和溶质性质都会影响柱性能。因此仅使用一两种探针溶质不足以对色谱柱进行排名。
