A Molecular Dynamics Study of a Reversed-Phase Liquid Chromatography Model

Published

February 1, 1999

Author(s)

J T. Slusher, Raymond D. Mountain

Abstract

We describe a molecular dynamics simulation study of a model of the reverse-phase chromatographic system. The model consists of a slab of aqueous solvent sandwiched between two walls having attached C₈ hydrocarbon chains at a surface coverage of 5.09 mol/m² or 32,6 {Angstrom}² / chain. Long-ranged Coulombic interactions are taken into account using the Ewald sum method of Rhee, et al. [Phys. Rev. B, 40, 36, 1989]. The density and solvent orientation profiles are computed as a function of distance from the walls. The density profiles are found to be sensitive to the treatment of the long-ranged electrostatic interactions. The presence of an organic cosolvent (methanol or acetonitrile) at 30.8 mole % has little effect on the chain structure, which is largely collapsed against the walls. We also estimate the change in residual Helmholtz free energy along the pore width for a methane solute in the acetronitrile/water system, which indicates that a substantial portion of the free energy driving force for retention occurs in an organic-rich layer of solvent adsorbed to the hydrocarbon phase.

Citation

Journal of Physical Chemistry B

Volume

103

Issue

No. 8

Pub Type

Journals

Keywords

acetonitrile, Helmholtz free energy, liquid chromatography, liquid-liquid interface, methanol, molecular dynamics, water

Citation

Slusher, J. and Mountain, R. (1999), A Molecular Dynamics Study of a Reversed-Phase Liquid Chromatography Model, Journal of Physical Chemistry B (Accessed December 13, 2024)