Adsorption at the Water/Hydrophobe Interface versus Partition into the Interior of the Hydrophobe: Quantitative Evaluation of the Solute Retention Selectivity at the Water/Hydrocarbon Interface

作者：Nakamura Keisuke; Saito Shingo; Shibukawa Masami^*

来源：Journal of Physical Chemistry C, 2018, 122(8): 4409-4418.

DOI：10.1021/acs.jpcc.7b12413

Molecular level understanding of the chemistry at the water/hydrophobe interface is crucial to chemical separation processes in aqueous media, such as reversed-phase liquid chromatography and solid phase extraction. However, direct observation of the behavior of molecules and ions at the interface in reversed-phase separation systems still remains a major challenge, and probing techniques that provide the spatial information of the distribution of molecules and ions are required. In this paper, the molecular distribution between the aqueous solution and alkyl-bonded silica particles is studied by surface-bubble-modulated liquid chromatography (SBMLC). We determine the distribution coefficients of various organic compounds referring to their accumulations onto the water/alkyl chain interface and into the alkyl chain layer from the bulk water by SBMLC. The bulk water-to-alkyl chain layer distribution coefficient is corrected for the contribution of the end capped silica surface to the solute retention using end-capped C-8- and C-18-bonded silica columns. The experimental data provide a picture of the spatial distribution of organic molecules in alkyl-bonded silica particles exposed to water. It has been revealed that the water/alkyl chain interface exhibits an accumulation selectivity for organic compounds which is quite different from that of the interior of the alkyl chain layer and the overall separation selectivity of the reversed-phase systems is determined by the relative sizes of the aqueous/hydrophobe interface and the hydrophobe.

• 出版日期2018-3-1