Retention properties of a spacer-bonded propanediol sorbent for reversed-phase liquid chromatography and solid-phase extraction

Abstract

The characteristic kinetic and retention properties of a silica-based, spacer-bonded propanediol sorbent for solid-phase extraction are described. The solvation parameter model is used to characterize the retention properties of the sorbent with methanol, propan-2-ol, acetonitrile and tetrahydrofuran in water as mobile phases. Retention occurs because of a more favourable cavity term for the solvated sorbent and because of more favourable stationary phase interactions with solutes containing π-and n-electrons. The capacity of the solute for dipole-type interactions is not important for most mobile phase compositions investigated, whereas all hydrogen bond-type interactions result in reduced retention. Plotting the system constants as a function of mobile phase composition provides a simple mechanism for interpreting the change in capacity of the chromatographic system for retention in terms of changes in the relative weighting of fundamental intermolecular interactions. A comparison is also made with a silica-based, cyanopropylsiloxane-bonded sorbent with the same range of mobile phase compositions. For solid-phase extraction, the difference in polar interactions between the two sorbents is unable to offset completely the differences in ease of cavity formation such that retention will always be larger for the cyanopropylsiloxane-bonded sorbent when the sample solvent is predominantly aqueous. These conclusions do not apply to normal-phase conditions where retention by the stationary phase is governed by the capacity of the sorbent for polar interactions and the relative ease of cavity formation is generally unimportant.