ABSTRACT
X-ray patterns can be obtained using either a powder diffractometer or a camera. Diffractometers find widespread use in the analysis of pharmaceutical solids. X-ray powder diffractometry (XRD) is the technique of choice to identify different polymorphic forms of a compound. X-rays are electromagnetic radiation lying between ultraviolet and gamma rays in the electromagnetic spectrum. XRD is widely used to determine the degree of crystallinity of pharmaceuticals. Conventionally, XRD patterns are obtained at room temperature under ambient conditions. Variable temperature XRD is a technique where XRD patterns are obtained while the sample is subjected to a controlled temperature program. XRD is an excellent technique to study drug-excipient interactions, provided the drug and the excipients are crystalline. The use of a cooling accessory permits XRD patterns to be obtained under subambient conditions. In pharmaceutical systems, the greatest utility of the technique is to monitor the crystallization of solutes in frozen solutions.
