X-Ray Diffraction – XRD

Introduction to XRD

X-ray diffraction (XRD analysis or XRPD analysis) is a unique method in determination of crystallinity of a compound. XRD is primarily used for

  • ID of crystalline material (used for regulatory purposes or during development.) 
  • ID of different polymorphic forms (“fingerprints” ).
  • Distinguishing between amorphous and crystalline material
  • Quantification of the percent crystallinity of a sample

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Knowledge about crystallinity is highly relevant, as a crystalline form is usually preferred in development: In contrast to amorphous material, a crystal has well-defined properties (melting point, solubility and IDR) – parameters that should be known in order to control your final product. The XRD method is described in Ph. Eur 2.9.33. The result from an XRD analysis is a diffractogram showing the intensity as a function of the diffraction angles.  Positive ID of a material using XRD analysis is based on accordance between the diffraction angles of a reference material and the sample in question.

Instrument and measuring principle

XRD analysis is based on constructive interference of monochromatic X-rays and a crystalline sample: The X-rays are generated by a cathode ray tube, filtered to produce monochromatic radiation, collimated to concentrate, and directed toward the sample. The interaction of the incident rays with the sample produces constructive interference (and a diffracted ray) when conditions satisfy Bragg’s Law (nλ=2d sin θ). This law relates the wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in a crystalline sample.

The characteristic x-ray diffraction pattern generated in a typical XRD analysis provides a unique “fingerprint” of the crystals present in the sample. When properly interpreted, by comparison with standard reference patterns and measurements, this fingerprint allows  identification of the crystalline form.

Technical info
Instrument Bruker AXS D8 Advance X-ray diffractometer with CuKa radiation, operated at 40 kV, 250 mA
Operating range 2-40 °2Theta (if required up to 150 °2Theta)
Temperature RT (temperature chamber available)
Humidity Ambient (humidity chamber available)
Sample amount App. 10 mg

XRD diffractogram

A diffractogram from an XRD analysis