Fully atomistic simulations of water/methanol mixtures of varying compositions (80/20 and 50/50) at chromatographic interfaces with different functionalizations are presented. The dynamical properties in terms of equilibration times and solvent exchange dynamics are characterized and found to depend on the different systems on the nanosecond time scale. The solvent density profile and the structuring of the stationary phase differ for derivatizations including (-CN, NO2, -NH2, -C 6H5) of the C18 chain. The time scale and intensity of the water exchange dynamics differs for the different realizations of the chromatographic systems and ranges from 200 to 500 ps. Water exchange rates depend on solvent composition as well as on the functionalization of alkyl chains. Simulations with acridine as a probe molecule provide atomistic insight into the slot model.