1 Introduction

The use of isothermal microcalorimetry is now widely accepted as a powerful tool for the study of a vast array of systems within industry. Microcalorimetry is routinely used for compatibility studies ^[1] (active excipient, excipient excipient interactions), stability ^{[2] , [3]} (shelf-life), degradation, ^[4] physical properties such as polymorphism ^[5] and crystallinity, ^[6] and can be used to probe surface characteristics of solid materials; ^[7] some of these concepts are dealt with in more detail (with particular attention to pharmaceutical issues) by Beezer in Chapter 9. Generally, the information sought on a given system is related to the kinetics of that system ( e.g. shelf-life). It is essential therefore that accurate/quantitative information can be derived for parameters such as rate and the rate constant. Also important is the quantity of material undergoing change in the system, which can be explored through the magnitude of the calorimetric signal and calculation of the enthalpy for that reaction. Knowledge of these parameters then allows a host of other thermodynamic and kinetic information to be derived from the system under study. ^{[3] , [8] [11]} A large proportion of calorimetric studies are performed using static/batch techniques, however, studies using batch mode techniques are generally unsuitable for the study of reactions that have a relatively short half-life such that the reaction is complete before the preparatory work required for static systems is carried out ^[3] (approximately 1 h), such as some...