Use of thermoanalytical methods in quantification of drug load in mesoporous silicon microparticles

Thermally carbonised mesoporous silicon microparticles were produced and loaded with two active pharmaceutical ingredients, ibuprofen and antipyrine. By combining the results measured with TG and DSC, reliable estimations for the degrees of the drug loads were obtained. To distinguish the drug adsorbed on the surfaces of the microparticles from that absorbed into the pores, the principle of thermoporometry on the DSC measurements was employed. According to the principle, the drug held in the capillaries of porous material has a depressed melting temperature because of the higher pressure of the drug in cavities with a curved interface. On the other hand, the drug located on the external surface of the microparticles exhibits the normal melting of bulk drug. The loading degrees obtained with the thermoanalytical methods ( 31 and 26 mass% for ibuprofen and antipyrine, respectively) were comparable with the results obtained with helium pycnometry ( the corresponding values were 33 and 28 mass%). Nitrogen sorption studies were not reliable for quantitative determinations due to the inability of nitrogen to penetrate in all pores, which might be blocked by the drug on the surface of the microparticles.