At its 160th session (March 2018) the Ph. Eur. Commission adopted a new version of one of its major general methods, which has undergone extensive revision. The chapter on Infrared Absorption Spectrophotometry (2.2.24) is one of the original cornerstones of pharmacopoeial testing, referenced in many general texts and more than 1200 individual monographs.
The chapter has been completely rewritten and its structure updated to include:
- the removal of monochromator instruments as they are now obsolete;
- an extended description of Fourier-transform spectrometers (FT-IR) using attenuated total reflection (ATR) and related criteria for the control of equipment performance;
- a new "principle" section, with distinction between near-, mid- and far-infrared;
- new sections on applications and limitations;
- a reduction from 7 to 4 band positions for verification of the wavenumber scale following the removal of monochromator instruments, and addition of slightly shifted band positions for ATR FT-IR instruments;
- guidance on the use of stored spectra and internal libraries;
- a description of procedures for the comparison of spectra.
It is highlighted that the new band positions – and the associated acceptable tolerances – proposed for the verification of the wavenumber scale have been established based on experimental data gathered during two series of round-robin tests by different laboratories using different instruments.
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