Effect of Acetonitrile on the Solute Distribution at the Heterogeneous Interface Region between Water and Hydrocarbonaceous Silica Revealed by Surface-Bubble-Modulated Liquid Chromatography

Abstract

The interface between water and a hydrocarbonaceous material is important because of its usefulness for separation of a variety of chemical compounds. In order to change the magnitude of accumulation of the compounds at the water/hydrophobe interface, water miscible organic solvents such as acetonitrile are often added to the aqueous solution. However, the origin of the effect of the organic solvents on the separation of solute compounds has not been fully elucidated. We used surface-bubble-modulated liquid chromatography to investigate the spatial distribution of various organic compounds on an alkyl-bonded silica in contact with an acetonitrile–water mixture (0–5% (v/v)). Our results show that the dependences of the bulk liquid-to-aqueous/alkyl chain interface and bulk liquid-to-alkyl bonded layer distribution coefficients for organic compounds on acetonitrile concentration in aqueous solution are quite different from each other. It has been revealed that acetonitrile slightly partitions into the interior of the alkyl chain layer, whereas it preferentially accumulates at the interface although the interfacial liquid layer at the interface consists of not only acetonitrile but also water. The addition of acetonitrile to the aqueous solution causes a distinct decrease of accumulation of the compounds having hydrophilic groups, while the change in retention of hydrophobic compounds is rather small.

Characterization of the Interfacial Liquid Layer Formed on Hydrophobic Packing Material Surfaces by Liquid Chromatographic Analysis of the Distribution of Ions and Molecules

“…This is because most chromatographic and spectroscopic methods cannot directly extract the information for the effect of the interface on the analyte or solvent distribution from the data obtained. On the other hand, we developed a new type of liquid chromatography, surface-bubble-modulated liquid chromatography (SBMLC), and demonstrated that SBMLC enables us to experimentally determine the respective contributions of the liquid/bonded layer interface and the bonded phase to the overall retention of the compound in the reversed-phase systems. − The experimental results obtained by SBMLC agreed well with the observation from the MD simulation. ,, …”

“…Determination of the Volume of the Interfacial Liquid Layer Formed on the Surface of the Alkyl-Bonded Phase. The bulk liquid phase volume in an RPLC column, V BL , can be determined using small inorganic ions with the same charge as probes according to the following equation [23][24][25][26][27][28]34 = −…”

Stationary-Phase Contributions to Surface Diffusion in Reversed-Phase Liquid Chromatography: Chain Length versus Ligand Density

“…The analyte-specific properties of the profiles, discussed in-depth in earlier work, , are of minor relevance here. (Recent studies focusing on mechanistic details of analyte retention can be found here. − ) Apart from the expected overall decrease in analyte density at z < z sp due to the increased elution strength of the mobile phase, changes in the analyte density profiles between 70/30 and 20/80 (v/v) W/ACN are related to changes in interfacial width.…”

Molecular Dynamics Study of the Relation between Analyte Retention and Surface Diffusion in Reversed-Phase Liquid Chromatography

“…This observation agrees with results from a recently developed technique, surface bubble-modulated liquid chromatography. 49,50 The relative contributions from partitioning and adsorption to retention (Table S4) show only little variation with the W/ACN ratio of the mobile phase, but they reflect analyte properties. Partitioning contributes (averaged over all W/ACN ratios) 31% to ethylbenzene retention, 27% to benzene retention, 14% to acetophenone retention, and 6% to benzyl alcohol retention in the RPLC mesopore model.…”