The use of micro-thermal analysis as a means of in situ characterisation of a pharmaceutical tablet coat

The technique of micro-thermal analysis (MTA) has been applied to a commercial sugar coated ibuprofen tablet in order to identify the ability of the method to differentiate between the coat and the tablet core and to characterise the thermal properties of both components using localised thermal analysis. Thermal conductivity measurements in conjunction with intensity histogram analysis indicated that differentiation across the coat/core interface was possible, with a bimodal distribution of pixel intensities corresponding to thermal conductivity noted. Localised thermal analysis studies indicated that the bulk response was dominated by the incorporated ibuprofen, with a discontinuity seen at ca. 70–80°C, corresponding to the published melting point of the drug. The coat showed a discontinuity at ca. 220°C that may be reasonably ascribed to the melting process. It was also noted that the coat showed a small discontinuity at a temperature corresponding to the melting of ibuprofen. In summary, the technique was shown to be capable of identifying the core/coat interface using thermal conductivity measurements, while localised thermal analysis experiments enable the operator to perform thermal analysis experiments on the individual components in situ.