The influence of the pH, the concentration, and the nature of the buffer on the retention and overloading behavior of propranolol (pK a =9.25) on Kromasil-C 1 8 was studied at 2.75<pH<6.75, using four buffers (phosphate, acetate, phthalate, and succinate), at three concentrations, 6, 20, and 60mM. The propranolol band profiles were recorded for three sample sizes, less than 1μg and 375μg (sample less concentrated than the buffer), and 7500μg (band more concentrated than the buffer). Results showed that the buffer concentration, not its pH, controls the retention time of propranolol, in agreement with the chaotropic model. The retention factor depends also on the nature of the buffer, particularly the valence of the basic anion. At moderate loading, the band profiles are well accounted for by a simple bilangmuir model (no adsorbate-adsorbate interactions) with the monovalent anions H 2 PO 4 - (pH 2.75), HOOC Ph COO - (pH 2.75), HOOC CH 2 CH 2 COO - (pH 4.16) and CH 3 COO - (pH 4.75), and by a bimoreau model (significant adsorbate-adsorbate interactions) with the bivalent anions - OOC Ph COO - (pH 4.75), - OOC CH 2 CH 2 COO - (pH 5.61) and HPO 4 2 - (pH 6.75). The isotherm were determined using the inverse method. The results show that both the saturation capacity and the equilibrium constant on the low-energy sites increase with increasing buffer concentration, a result similar to that observed with neutral salts. For bivalent anions, the adsorbate-adsorbate interactions are much stronger on the low than on the high energy sites. The density of high energy sites is lower and the equilibrium constant on the low energy sites are higher with bivalent than with univalent anions. These results are consistent with the formation of a propranolol-buffer (2:1) complex with bivalent anions.