Adsorption of allopurinol and ketotifen by chitosan

The experimental work of studying the adsorption of ketotifen and allopurinol by chitosan focused on determining the solubilities and the adsorption isotherms of the adsorbates employed in this study. The adsorption of the aforementioned compounds by chitosan was studied using the rotating bottle method. The concentrations, both before and after the attainment of equilibrium, were determined with the aid of a reversed-phase high-performance liquid chromatography column. The results of these studies demonstrated that ketotifen and allopurinol are both adsorbed by chitosan. The nonlinear Langmuir-like and the Freundlich models both were applied to the experimental data. The correlation coefficients obtained from the nonlinear Langmuir-like model were better than those obtained from Freundlich model, suggesting that allopurinol and ketotifen interacted with certain specific binding sites on the chitosan surface. The allopurinol adsorption experiments indicated that the particle size of chitosan and therefore the surface area can significantly affect the Langmuir capacity constant, while the affinity constants are statistically the same. As expected from the solubility studies, the ketotifen adsorption experiments at 2 different pHs (7 and 10) showed that the adsorption affinity at pH 10 was much higher than at pH 7. What was not expected was that the capacity constants were significantly different, suggesting that further studies are needed using common ion buffers and multicomponent adsorption for the proper mechanism to be determined.