Solid state forms of complex molecular structures have diffraction patterns characterized by many and overlapped reflections. In such cases, data interpretation can be quite demanding and explains why for many years XRPD has been almost uniquely employed as a fingerprinting technique, both for qualitative and quantitative assessments.
During the last 10-15 years, an impressive development in instrumentation, computer technology and powder diffraction experimental techniques [13,14] and methodologies [15-22] took place, which upgraded XRPD from a support technique to a fundamental one. Furthermore, the recent development of total scattering techniques (i.e. techniques that interpret both Bragg and diffuse elastic scattering) has extended the use of powder diffraction to nano- or non-crystalline (i.e. liquid and amorphous) materials [23-25].
SR-XRPD has major advantages over laboratory XRPD
Laboratory XRPD is suitable for routine and structural analyses of medium difficulty. However, the identification of polymorphs with similar structure, their quantification in complex mixtures or the detection of low levels of impurities (less than a few %) require SR-XRPD.
The experimental artefacts that characterize laboratory XRPD prevent it in such cases to ascertain the structural and microstructural properties of pharmaceutical compounds [4, 22, 23]. Furthermore, SR-XRPD allows the detection of unexpected structural changes or unknown forms during manufacturing conditions, e.g. in the field of pharmaceuticals, kinetic studies at the msec scale and the application of XRPD to more complex systems, e.g. biologicals molecules.