Preparative high performance liquid chromatography (PHPLC) is used for separation of compounds with very similar physical and physico-chemical properties. The separation of the above mentioned compounds by traditional chemical engineering processes cannot be done or only with low efficiency. A mathematical model describing separation, and computer programme on a PC based on that model provide respectful support during the elaboration of a preparative liquid chromatographic process, which with the help of a number of experiments, can be reduce the demand of chemicals and result in cost savings. Authors present in this publication a mathematical model based on multicomponent adsorption equilibrium (competitive Langmuir isotherm) of displacement preparative liquid chromatography and its numerical solution, PC programme and the results of computation.