MICROSCOPIC SIMULATION OF SOLUTE TRANSFER IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY

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