Macroscopic attenuated total reflection (ATR) infrared imaging is applied to study the dissolution of realistically sized hydroxypropyl methylcellulose (HPMC) tablets. The water intake into in situ compacted tablets and pre-compacted tablets was studied as a function of compaction pressure. Rigorous analysis of the imaging datasets show that the speed of water intake into HPMC tablet is approximately 4 μm/min and is hardly affected by the studied range of compaction pressures or the type of ATR crystal used (diamond or ZnSe). This constant speed of water intake implies that leakage ('creeping') of water into the space between the tablet and the ATR crystal does not occur. It is shown that the radius of the HPMC tablet initially expands to twice the original radius due to swelling.
Jaap van der Weerd and Sergei G. Kazarian, "Validation of Macroscopic Attenuated Total Reflection-Fourier Transform Infrared Imaging to Study Dissolution of Swelling Pharmaceutical Tablets," Appl. Spectrosc. 58, 1413-1419 (2004)