STUDY OF THERMODYNAMICS AND KINETICS OF SORPTION OF METHYL SALICYLATE BY POLYVINYL CHLORIDE USING HIGH PRESSURE LIQUID CHROMATOGRAPHIC METHOD (HPLC)

The methodology used in the study of the thermodynamics and kinetics of sorption of low molecular weight solutes, commonly used in pharmaceutical formulations, by polymers used for packaging provides the basis of this research project. A high pressure liquid chromatographic method based on the frontal mode of development was investigated by using methyl salicylate as a probe in the aqueous solution and polyvinyl chloride served as the stationary phase of the HPLC system. In this method aqueous solution of methyl salicyclate was pumped through the polyvinyl chloride column at constant temperature and flow rate and the effluent concentration was related to the rate and extent of sorption. In order to compare the results obtained by the chromatographic method, the equilibrium and rate parameters for the sorption of methyl salicylate by polyvinyl chloride and plasticized polyvinyl chloride were first obtained by the static method. The values of the apparent partition coefficient obtained by the static method and by the chromatographic method based on the characteristic point showed good agreement for sorption by polyvinyl chloride. The frontal chromatographic method underestimated the magnitude of the apparent partition coefficient and the apparent diffusion coefficient for the sorption of methyl salicylate by the plasticized polyvinyl chloride. The apparent diffusion coefficient for the sorption of methyl salicylate by polyvinyl chloride could not be evaluated by the chromatographic method because of very slow diffusion into the polymer matrix.; The results of this study indicate that, although, the apparent partition coefficient and the apparent diffusion coefficient are somewhat underestimated by the frontal chromatographic method, it should still be a useful method for rapid evaluation of the thermodynamics and kinetics of sorption of pharmaceutically important solutes by polymers.