It is commonly acknowledged that the retention of non-ionized polar analytes on polar stationary phases is governed by hydrophilic partitioning and surface adsorption. However, it has been difficult to evaluate whether partitioning or adsorption is the dominant mechanism for a specific polar compound on a polar stationary phase. We have developed a simple method based on the thermodynamic principle of partitioning to quantitatively investigate the retention contributed by the partitioning or adsorption mechanism. By varying phase ratio through changing salt concentration in the mobile phase, we were able to determine the distribution coefficients of cytosine between the adsorbed water layer and the mobile phase containing various levels of acetonitrile. The retention factors of cytosine attributed to partitioning and adsorption were quantitatively determined. The results demonstrate that the dominant retention mechanism for cytosine is hydrophilic partitioning on ZIC-HILIC, XBridge Amide and LUNA-HILIC columns.

众所周知，非电离极性分析物在极性固定相上的保留受亲水分配和表面吸附的控制。然而，很难评估是分配还是吸附是特定极性化合物在极性固定相上的主要机制。我们开发了一种基于分配热力学原理的简单方法，用于定量研究分配或吸附机制贡献的保留。通过改变流动相中的盐浓度来改变相比，我们能够确定吸附水层和含有不同含量乙腈的流动相之间胞嘧啶的分配系数。定量测定归因于分配和吸附的胞嘧啶保留因子。结果表明，胞嘧啶的主要保留机制是 ZIC-HILIC、XBridge Amide 和 LUNA-HILIC 色谱柱上的亲水分配。