An investigation into the use of micro-thermal analysis for the solid state characterisation of an HPMC tablet formulation

The use of micro-thermal analysis (mu TA(TM)) as a novel means of different iating between components in a model tablet formulation is described. This technique involves a modification of atomic force microscopy (AFM) such tha t the standard AFM tip is replaced with a Wollaston wire, thereby allowing the probe to act as a thermistor and temperature probe. Consequently it is possible to map not only the topology but also the thermal conductivity of the sample. Furthermore, it is possible to apply a heating signal to the ma terial and thereby to perform thermal analysis on highly localised regions of the sample. Compacts were prepared comprising ibuprofen, HPMC E4M prem a nd 1:1 mixes of the two components and analysed using a mu TA(TM) micro-the rmal analyser. The surface topology and conductivity images of the three sy stems are reported. In addition, the ability of the technique to perform th ermal analysis on highly specific regions of the sample is described. The m ethod was able to differentiate between the components of the sample on the basis of micro-thermomechanical experiments. The implications of the use o f the technique for the study of pharmaceutical tablets is discussed. (C) 1 999 Elsevier Science B.V. All rights reserved.