Abstract: An apparatus for optimizing the liquid chromatographic separation of a sample comprises means for performing liquid chromatographic separations at selectable values of an optimization parameter, such as the composition of the mobile phase. Based upon measured chromatographic data of the sample and upon a mathematical model, the retention behavior of the sample as a function of the optimization parameter is derived by data processing means and displayed on a display means. An input means permits the chromatographer to select from the displayed retention behavior a desired value of the optimization parameter. In response to such a selection, the resulting chromatogram for this value is calculated and displayed. By means of the displayed retention behavior and the corresponding chromatograms, the chromatographer can quickly locate a value of the optimization parameter for which optimal results can be expected. Then, a chromatographic separation of the sample is performed with the selected value.