[Use of mercury porosimetry, assisted by nitrogen adsorption in the investigation of the pore structure of tablets].

The microstructure of pharmaceutical solid dosage forms (porosity, pore volume-size distribution, specific surface area) can be investigated by different methods. Mercury porosimetry and nitrogen gas adsorption have been widely used to characterize the pore structure of tablets because these methods enable the determination of porosity and pore size distribution in one step. The two techniques are based on different physical interactions and cover specific ranges of pore size. Mercury porosimetry determines mesopores and macropores, whereas gas adsorption covers the micropore range. The aim of this study was to investigate the relationship between the compression force and the structure of tablets containing theophylline. The porosity parameters determined with mercury porosimetry and nitrogen adsorption were compared. The results indicated a good correlation between the applied compression forces and the porosity parameters of the tablets. The pore volume-size distributions, the pore size frequencies and the specific surface areas obtained with mercury porosimetry and nitrogen adsorption were not equal, which can be attributed to the different measurement ranges and to the complexity of the pore structures. Our results allow the conclusion that mercury porosimetry, assisted by nitrogen adsorption as a complementary technique, is an acceptable method to achieve a proper characterization of the internal structure of tablets.