University of Wisconsin - River Falls, River Falls, WI, USA.
J Chromatogr A. 2011 Oct 7;1218(40):7110-29. doi: 10.1016/j.chroma.2011.07.085. Epub 2011 Aug 3.
The contribution of cation exchange to solute retention for type-B alkylsilica columns (made from high-purity silica) has been examined in terms of the hydrophobic-subtraction (H-S) model of reversed-phase column selectivity. The relative importance of cation exchange in the separation of ionized bases by reversed-phase chromatography (RPC) varies with (a) column acidity (values of the column cation-exchange capacity C), (b) mobile-phase pH and buffer concentration, and (c) the nature of the buffer cation. The effects of each of these separation variables on cation retention were examined. The contribution of cation exchange (and other ionic interactions) to solute retention is represented in the H-S model by properties of the solute (κ') and column (C), respectively. Values of κ' for 87 solutes have been examined as a function of solute molecular structure, and values of C for 167 type-B alkylsilica columns have been related to various column properties: ligand length (e.g., C(8) vs. C(18)) and concentration (μmol/m(2)), pore diameter (nm), and end-capping. These results contribute to a more detailed picture of the retention of cationic solutes in RPC as a function of separation conditions. While previous work suggests that the ionization of type-B alkylsilica columns is generally negligible with mobile-phase pH<7 (as a result of which cation exchange then becomes insignificant), the present study provides evidence for cation exchange (and presumably silanol ionization) at a pH as low as 3 for most columns.
已根据反相色谱柱选择性的疏水取代（H-S）模型，考察了 B 型烷基硅烷柱（由高纯度硅胶制成）中阳离子交换对溶质保留的贡献。反相色谱法（RPC）中离子化碱基分离时，阳离子交换的相对重要性随（a）柱酸度（柱阳离子交换容量 C 的值）、（b）流动相 pH 值和缓冲液浓度以及（c）缓冲阳离子的性质而变化。考察了这些分离变量对阳离子保留的影响。H-S 模型中，溶质（κ'）和柱（C）的特性分别代表了阳离子交换（和其他离子相互作用）对溶质保留的贡献。考察了 87 种溶质的 κ'值与溶质分子结构的关系，并将 167 种 B 型烷基硅烷柱的 C 值与各种柱性质相关联：配体长度（例如 C(8)与 C(18))和浓度（μmol/m(2))、孔径（nm）和端基封闭。这些结果有助于更详细地了解 RPC 中阳离子溶质保留作为分离条件的函数。尽管之前的工作表明，当流动相 pH<7 时（由于这种情况，阳离子交换变得无足轻重），B 型烷基硅烷柱的离子化通常可以忽略不计，但本研究为大多数柱在 pH 低至 3 时的阳离子交换（和可能的硅醇离子化）提供了证据。
