THE KINETICS OF ADSORPTION OF SOME ORGANIC CATIONS ON TO AN INSOLUBLESODIUM POLYPHOSPHATE

The kinetics of adsorption of the hydrochlorides of chlorpromazine, pr opranolol, quinine, and quinidine on to an insoluble sodium polyphosph ate, Maddrell's phosphate type II (MPI), have been studied in vitro. T he data have been fitted to a three-compartment model, in which one co mpartment represents the aqueous solution of adsorbate and the other t wo compartments represent hypothetical adsorption sites. One site is l abile, i.e., adsorption (and desorption) occur very rapidly, while the second sire is a sink at which the adsorption density slowly increase s until it eventually dominates the total adsorption density. The init ial adsorption rates of the cations increase with temperature and, wit h the exception of quinidine, are very rapid. The adsorption densities obtained for the drugs substantially exceed the predicted densities a nd it is suggested that the drugs may form an adhesive layer of insolu ble (drug-polyphosphate) complex at the MPI surface which then acts as a diffusion barrier to further uptake.