7.4. X-ray crystallography

Abstract

Publisher Summary X-ray diffractometry is a generally applied method in the pharmaceutical industry to investigate the polymorphism of drug substances, as well as to monitor the occasional changes of the applied modification during different steps of the formulation procedure. Although single-crystal X-ray diffractometers provide the most precise information on crystal structure of drug substances: unit cell data, molecular packing, hydrogen-bonds, conformation and absolute configuration, in the majority of cases the X-ray powder diffraction technique is applied for the identification and quantification of polymorphic phases because it does not need single crystals and it is a considerably less expensive method. The main application field of single-crystal X-ray crystallography is the determination of molecular structures. However, if a single-crystal diffractometer is available, the powder diffraction patterns calculated from the single-crystal data can be used to prove whether the patterns obtained with X-ray powder diffractometry were made of a pure phase or not and whether they were falsified by preferred orientation—that is, the intensity is smaller or greater than the calculated value.