The main focus of the research presented in this thesis is to develop a robust and easy-to-use photocalorimeter to allow a quantitative assessment of the photostability of pharmaceutical compounds. As a result, a novel photocalorimeter was successfully developed. Initially a Xe-arc lamp was used as a light source, but this was found to be problematic, rendering quantitative analysis of data challenging. A novel approach using light-emitting diodes (LEDs) as a light source was developed; this approach demonstrated much potential in photostability testing. Using the prototype systems a suitable method to allow measurement of the radiant energy delivered to the sample during a photochemical process was investigated. The best system appeared to be the photodegradation of 2-nitrobenzaldehyde (2NB). Although promising as a test and reference reaction, it was found that 2NB was sensitive to non-photochemical processes and the reaction was complex which means further work on its application in this area must be undertaken. The application of chemometric analysis as an approach to interpret complexity in Isothermal Calorimetric data was then studied. A three-step consecutive reaction was used to demonstrate the applicability of principal component analysis to determine the number of reaction steps and reaction parameters in a process. The application of photocalorimetry for the study of a known photosensitive drug, nifedipine was investigated. The photolysis of nifedipine in solution was studied under full spectrum lighting and under specific wavelengths for the determination of causative wavelength (s). The data showed the photodegradation of nifedipine to be particularly sensitive at 360 nm. No significant photosensitivity was detected above 370 nm. Finally a novel autobalance power supply, currently under development, designed to improve the performance of the photocalorimeter is described
