Adsorption mechanisms of small aromatic compounds in cross-linked dextran gel

A series of 12 small aromatic compounds, along with glucose and cellobiose, was selected to analyze how structural and physicochemical properties influence the adsorption of small aromatic compounds onto cross-linked dextran resin (Sephadex® G-25) in aqueous chromatography. This group of compounds contain structural features that are common in phytochemicals, such as methoxy, hydroxyl and hydroxymethyl groups and glucosides. Retention factors of these compounds were measured in similar conditions at different temperatures and compared with their structural and physicochemical information. Enthalpy-entropy compensation plot distinguished groups of compounds that are expected to have differing adsorption mechanisms. Retention factors at 21°C varied for the aromatic compounds from 1.27, for benzyl ß-D-glucopyranose, to 2.48 for 3-methoxyphenol. Temperature increase from 21°C to 50°C had a mild effect on the strength of π-interaction mediated adsorption. However, it diminished hydrogen bonding related adsorption effects in the aromatic compounds. An explanation of the variations in the adsorption strength is proposed based on the structure effects of the compounds. Inductive- and resonance effects affecting π-interaction are considered together with hydrogen bonding and steric effects. An incremental adsorptivity model is used to demonstrate how the observed retention factors originate from these structure effects, and how they account for the differences with the measured retention factors in different temperatures.