asymmetry of a peak such that, relative to the baseline, the front is steeper than the rear. In paper chromatography and in thin-layer chromatography, the distortion of a zone showing a diffuse region behind the zone in the direction of travel.
Sources:
Orange Book, 2nd ed., p. 96 (https://media.iupac.org/publications/analytical_compendium/)
PAC, 1993, 65, 819. 'Nomenclature for chromatography (IUPAC Recommendations 1993)' on page 837 (https://doi.org/10.1351/pac199365040819)