An elution procedure in which the stationary phase is more polar then the mobile phase. This term is used in liquid chromatography to emphasize the contrast to reversed-phase chromatography.
Source:
PAC, 1993, 65, 819. 'Nomenclature for chromatography (IUPAC Recommendations 1993)' on page 826 (https://doi.org/10.1351/pac199365040819)