Simultaneous Measurements of X-ray Diffraction (xrd) and Differential Scanning Calorimetry (dsc) Data under Controlled Humidity Condition: Instrumentation and Application to Studies on Hydration, Dehydration, and Rehydration Processes of Pharmaceutical Compounds

Hydration and dehydration reaction processes of many organic and inorganic compounds accompany phase changes, and X-ray diffraction (XRD) is a very powerful technique for studying the reaction processes. Thermal analysis is another important technique often used to obtain information needed for understanding the reaction processes. Commercially available instruments for XRD and thermal analysis had been developed separately, and an XRD instrument is commonly used only for XRD analysis and a TG-DTA (thermogravimetry-differential thermal analysis) instrument for thermal analysis. A comparison between XRD data and thermal analysis data will provide a deep understanding of the hydration and dehydration reaction processes. However, these reaction processes are generally kinematical, depending on their thermal history and environmental factor such as humidity, as will be shown later in the results and discussion section [1, 2]. Therefore, it is of fundamental importance to measure XRD data and thermal analysis data at the same time and under the same environmental conditions, in particular, when the humidity is involved as one of the environmental factors in the reaction processes. Fawcett et al. reported the construction of an instrument for simultaneous measurements of XRD data and differential scanning calorimetry (DSC) data under the same temperature and atmospheric conditions. The instrument was equipped with a position sensitive proportional counter (PSPC) for rapid scanning of whole patterns during elevation or falling of the temperature, and it was used for studying performances of polymers and catalysis [1, 3]. Other instruments, developed for XRD-DSC studies, were equipped with a rotating anode generator and a scintillation counter [4] or a combined system of synchrotron radiation with PSPC [5]. Recently, we developed a new XRD-DSC instrument, as a commercially available laboratory system, by assembling a DSC unit on a standard XRD goniometer in order to achieve a design concept of reliable and simple in operation [6, 7]. A humidity control unit could also be equipped with the present system, and it can be used for studying hydration and dehydration processes of organic and inorganic materials such as pharmaceutical compounds, some of which are unstable under high humidity conditions. In this paper, special features of the instrument are described, and examples on studying hydration, dehydration and rehydration processes of trehalose dihydrate under various humidity conditions are presented. THE RIGAKU JOURNAL VOL. 21 / NO. 1 / 2004, 25–30