X-Ray Diffraction (XRD)

Materials appropriate for x-ray diffraction (XRD) analysis include powders, metals, pharmaceuticals and industrial minerals. A primary method for identifying crystalline materials is x-ray diffraction. When a solid sample is bombarded with x-rays, a random scattering of these x-rays occurs from the interaction with the atoms’ electronic structure. This interaction produces x-rays from the sample, some of which interfere with each other.

In certain directions, if the interference is constructive, an x-ray wave of enhanced intensity is produced; in other situations, the x-rays can cancel each other out and all intensity is eliminated. This additive scattering from a three-dimensional crystalline material is called diffraction.

Identification of the crystalline structure, based on the resulting diffraction pattern, is made using various computerized search programs, comparing the experimentally determined interatomic spacings with the JCPDS-ICDD database of reference compounds. Elemental analysis using the electron microprobe often assists in the search for a match with the reference library.

XRD allows the identification of compounds with differing crystalline structures, even though they have the same chemical composition, i.e., polymorphs.

Instrumentation

McCrone Associates uses two automated, computer-controlled Rigaku x-ray diffraction systems fitted with extensive data processing capabilities:

Rigaku MicroMax-007 X-ray diffraction system with Cu rotating anode x-ray source and SPIDER area detector for small particle analysis. The instrument can analyze small amounts (a few mg) of material in the form of powders (i.e., limited quantities of API), particles down to 10 µm in size, and some surfaces.