Microscopic Simulation of Solute Transfer in Reversed Phase Liquid Chromatography

Abstract

Solute retention in reversed phase liquid chromatography is driven by the free energy gradient on passing from the polar mobile phase into the nonpolar stationary phase. Only a partial understanding of retention exists currently. We present large scale molecular dynamics simulations of the transfer of a simple nonpolar solute from a water/methanol solvent mixture into a C 18 stationary phase at room temperature. In addition to a detailed examination of the local environment of the solute, we compute the excess chemical potential profile. The overall free energy change is consistent in magnitude with that expected for hydrophobic transfer from water rich to oil phases, but specific interfacial effects draw into question bulk partitioning models.

Changes in the structure of tethered chain molecules as predicted by density functional approach

“…The studies included scaling theories [13][14][15], classical self-consistent field methods [16,17], single chain mean-field methods [18], density functional theories [18][19][20][21][22] and computer simulations [23][24][25][26][27][28][29][30][31][32][33][34]. In our opinion, particularly important for further theoretical studies of systems involving tethered chains is the development of density functional theory (DFT) [20,21,[35][36][37][38][39][40][41][42] that is based on the approach proposed by Yu and Wu [43].…”

Influence of Residual Silanol Groups on Solvent and Ion Distribution at a Chemically Modified Silica Surface

“…With increasing acetonitrile content in the mobile phase, water is driven further outward to the bulk region, extending the interface width. In previous simulations of RPLC systems partitioning of the aqueous/organic mobile phase at the hydrophobic interface was observed for a C 18 -bonded phase in water/methanol, 12,20,[23][24][25][26] and for a C 8 -bonded phase in water/methanol and in water/ acetonitrile. 13,23 Solvent partitioning at the hydrophobic interface and the retreat of water toward the bulk region at increasing acetonitrile content in the mobile phase also persist in the ionic case ( Figure 2B).…”

New insights on the retention mechanism of non-polar solutes in reversed-phase liquid chromatographic columns

“…The elucidation of the retention mechanism in reversedphase liquid chromatographic columns has triggered intensive studies during the last two decades and up to now two principal mechanisms have been proposed [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]: adsorption of all constituents of the mobile phase, including the solute, on the tips or/and the stem of the hydrocarbon chains of the stationary phase and partition of the solute only molecules between the mobile phase and cavities formed within the hydrocarbon chains. In a recent study we have shown that the dominant retention mechanism in reversed-phase C 18 chromatographic columns is due to adsorption, whereas the partition is likely only for solutes with small and non-polar molecules [1].…”