<941> X-Ray Powder Diffraction

Type of Posting: Notice of Adoption of Harmonized Standard

Posting Date: 30-Apr-2021

Official Date: 01-May-2022

Expert Committee: General Chapters–Physical Analysis (GCPA)

Coordinating Pharmacopeia: European Pharmacopeia

The revision to the harmonized standard for 〈941〉 Characterization of Crystalline and Partially crystalline Solids by X-Ray Powder Diffraction (XRPD) has been approved by the Pharmacopeial Discussion Group (PDG) as described in its PDG Stage 4 sign-off cover sheet. The chapter has been formally approved by the General Chapters–Physical Analysis Expert Committee in accordance with the Rules and Procedures of the Council of Experts.

The changes from the current version of the chapter are:

  • In the beginning of the monograph, added the statement: “Portions of this monograph that are national USP text, and are not part of the harmonized text, are marked with symbols  symbol to specify this fact.
  • Introduction
    • In the first paragraph the term “crystallite” is clarified, and the particle orientation was replaced with preferred orientation.
  • Principle
    • In the first paragraph the phrase “scattered X-rays” was changed to “elastically scattered X-rays”.
    • The second paragraph was clarified to indicate that the discussion is for a polycrystalline powder.
    • Deleted “crystallinity” and added “microabsorption” for the factors that affect the intensity in the third paragraph. Additional minor editorial changes were done.
    • Figure 2 was replaced with a better-quality figure.
    • Minor editorial changes were done in the last paragraph.
  • Instrument
    • Minor editorial changes were done in the first paragraph of Instrument set-up sub-section for clarification.
    • In the second paragraph the term “parallel collimator” was replaced with the term “Soller slit,” which is a better representation of the component. It was further clarified that the receiving slit is used only when a 0D detector is present. The revision also added hybrid photon counting detectors as more common detectors.
    • In the X-Ray radiation sub-section, the definition of polychromatic radiation as “Bremsstrahlung or white radiation” was added. Silver was also added as a utilized principal radiation source. The cobalt description as most used anode for organic substances was deleted. 
  • Control of the Instrument Performance
    • Silicon powder or α-alumina (corundum) were added as examples of certified reference materials.
  • Qualitative Phase Analysis (Identification of Phases)
    • The comparison of diffraction patterns to “comparison data” was changed to comparison to “reference data”.
    • The recommended diffraction pattern in a 2θ-range for most organic crystals was changed from “as near 0° as possible to at least 40°” to “as near to 0° as possible to at least 30°”.
  • Quantitative Phase Analysis
    • The last paragraph was changed to state that: “Amounts of crystalline phases as small as 10 % may usually be determined in solid matrices, and in favorable cases amounts of crystalline phases less than 10 % may be determined”.
  • Estimate of The Amorphous and Crystalline Fractions 
    • The definition of the terms for the % crystallinity formula in the second bullet were revised for clarification.

Should you have any questions about this General Chapter, please contact Edmond Biba (301-230-3276 or exb@usp.org). For any questions about the PDG and its processes, please contact Richard Lew at (240-221-2060 or rll@usp.org).