Chemical characterization with XPS of the surface of polymer microparticles loaded with morphine

Hydrophilic matrices are a potentially useful option for the development of oral controlled–release formulations. The porous surface of these particles makes it possible to control or modify release of the active principle after administration. As a result, such formulations can be used in liquid controlled–release pharmaceutical formulations. We investigated a method of spontaneous drug encapsulation to prepare ethylcellulose polymer microparticles (since the polymer is synthetic rather than natural the final suspension is called pseudolatex) filled with morphine hydrochloride. Morphine is incorporated to water during the synthesis process and thus it is microencapsulated inside the micelles that give rise to the final microparticles. X-ray photoelectron spectroscopy (XPS), a technique that can identify elements in a sample without destroying it, was used for the chemical analysis of the surface of these microspheres. The results demonstrated the complete absence of morphine from the microsphere surface, which was taken as evidence that the drug had been completely encapsulated.