Characterisation of the Ion Exchange Reaction Between Propranolol-H+ or K+ with Amberlite™ IRP 69 Resin by Both, Isothermal Titration Calorimetry and (Flame) Photometric Equilibrium Analysis

The model system propranolol hydrochloride (PROP-HCl)/Amberlite was studied in terms of equilibrium concentrations and amount drug bound to the ion exchanger, and compared to the system potassium chloride (KCl)/Amberlite. It was found that both the affinity and exchange capacity of Amberlite for PROP-H+ ions is higher than for K+. Specific heat effects of the exchange reaction measured by isothermal calorimetry and spectroscopy revealed that even at the lowest degree of loading with propranolol, the heat effects surprisingly change continuously with the degree of loading, while they are constant for potassium. Involvement of non-specific forces in the binding of propranolol- H+ to Amberlite is discussed as a possible reason for this behaviour.