H-1-NMR MICROSCOPY OF TABLETS

A H-1-nuclear magnetic resonance (NMR) microscopy method was utilized for the first time to determine the porosity distribution of physicall y intact tablets. The main advantage of this newly developed method wa s that porosity cross sections through whole tablets or specific locat ions could be obtained without mechanically destroying the tested tabl et. This was achieved by filling tablet cavities with silicone oil und er vacuum. The amount of silicone oil locally within the tablet was th en determined by H-1-NMR microscopy, revealing the inverse inner struc ture. To reduce the measuring time, a paramagnetic gadolinium complex was added to the silicone oil. The cross sectional signals produced by H-1-NMR microscopy through the tablet were transformed into a color i mage by a specially designed computer graphic program. To improve the signal-noise ratio an algorithm of 3D-filtering was introduced. The ma ximal spatial resolution achieved with this method was about 95 mu m f or a cube's edge length corresponding to some 380 000 positions in a 9 -mm-diameter compression-coated tablet. Uneven porosity distributions within tablets, cracks, or cavities could be visualized with this newl y developed method. Different compaction mechanisms were observed with plastic- or brittle-type tablets. The different states of densificati on during compaction of powders could be detected. The integrity of co mpression coatings was determined to be dependent on the pressure load and the location of the core within the coat.