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Application of X-ray powder diffraction in pharmaceutical sciences Dr. Peter Sieger, Boehringer Ingelheim Pharma KG The tendency for pharmaceutical solids to crystallize in multiple crystal forms and the significance of this phenomenon (polymorphism) have been demonstrated (ref. 1, 2). Since polymorphism can affect the chemical, biological and pharmaceutical properties of a drug, it is very important to detect polymorphic, solvated or amorphous forms of the drug substance. Solid state properties, like crystallinity, thermal and hygroscopical behaviour as well as the tendency to form different crystalline modifications (polymorphism) under varying crystallisation conditions is of special interest for the developability of a new active pharmaceutical compound. X-ray powder diffraction is a very powerful and widely used analytical tool among the variety of existing techniques to study these properties. X-ray powder diffraction is used in simple routine experiments to measure crystallinity and/or phase purity, in temperature and/or humidity dependent experiments to study solid state phase transformations under the influence of varying temperature and/or humidity and in collecting highly resolved diffraction data for elucidation of structures which can not be solved from single crystal data. The last issue is certainly the most challenging task because pharmaceutical solids normally crystallize in large molecular structures (sometimes with several thousand Å3 volume) with low symmetry (more than 90 % of the compounds crystallize in monoclinic or triclinic space groups) and in addition the scattering properties are normally also very low. References: |
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