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 (μTA™) as a novel means of differentiating between components in a model tablet formulation is described. This technique involves a modification of atomic force microscopy (AFM) such that 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 material and thereby to perform thermal analysis on highly localised regions of the sample. Compacts were prepared comprising ibuprofen, HPMC E4M prem and 1:1 mixes of the two components and analysed using a μTA™ micro-thermal analyser. The surface topology and conductivity images of the three systems are reported. In addition, the ability of the technique to perform thermal analysis on highly specific regions of the sample is described. The method was able to differentiate between the components of the sample on the basis of micro-thermomechanical experiments. The implications of the use of the technique for the study of pharmaceutical tablets is discussed.