ABSTRACT
Isothermal calorimetry is the measurement of heat absorbed or released by a chemical or physical process, at a constant temperature, with time. Isothermal microcalorimetry is the measurement of such heats on a microwatt scale and is a technique which has been commercially available for around 15 years (1). Microcalorimetry (henceforth taken to mean isothermal in this chapter) offers a range of advantages over many other analytical techniques. For example, the instrument does not degrade nor intrude upon the sample. Neither is it dependent on the physical nature of the subject under study. The sample can be a solid, liquid or gas or, indeed, any heterogeneous mixture. This means it is possible to study most pharmaceutical preparations directly, the only consideration being to ensure the subject will fit in the microcalorimetric ampoule. Microcalorimeters measure the heat changes for all the reactions occurring simultaneously within the sample. This property has both benefits and drawbacks; it allows the study of many complex reactions that are outside the scope of other analytical tools but can lead to complexities in the analysis of the data. It also means that poor sample preparation can lead to erroneous heat-flow signals.
