General chapter 2.2.46. Chromatographic separation techniques has been revised to incorporate the provisions of the pharmacopoeial harmonisation text, signed-off by the Pharmacopoeial Discussion Group (PDG) on 28 September 2021. The revised chapter is now available in the 11th Edition of the Europe Pharmacopoeia (Ph. Eur. 11.0, implementation date: 1 January 2023).
This general chapter applies to chromatographic analytical procedures and supplements the general chapters on Thin-layer chromatography (2.2.7), Gas chromatography (2.2.28), Liquid chromatography (2.2.29) and Size-exclusion chromatography (2.2.30). In addition to definitions of chromatographic features, it contains system suitability requirements for LC and GC procedures, complementing those given in the individual monographs.
The main changes made for harmonisation purposes are:
- the signal-to-noise ratio is based on a baseline of 20 times the peak width at half height but if this is not obtainable, a baseline of at least 5 times the width at half-height is permitted;
- the default symmetry factor range has been extended from 0.8-1.5 to 0.8-1.8; it applies to both tests and assays;
- the text now states that retention times and relative retentions are not requirements but are given for information in the monographs;
- the system repeatability requirement in the assay now applies to both active substances and excipients, with a target value of 100 per cent for a pure substance;
- with regard to adjustments of chromatographic conditions, it is stressed that such adjustments are made only on the basis of the pharmacopoeial procedure. The fact that compliance with the system suitability test is always required (but is no longer the only factor prompting adjustments), that additional verification tests may be required when adjustments are made to a pharmacopoeial procedure and that multiple adjustments would trigger the need for a risk assessment is also clearly stated;
- for liquid chromatography with isocratic elution, the harmonised conditions for adjustment of the stationary phase are stricter than in the former chapter; adjustments of column dimensions are now based on the L/dp ratio, as was already the case in United States Pharmacopeia (USP) chapter <621>, but with stricter requirements; harmonised conditions are also described for the adjustment of mobile phase composition, flow rate and injection volume;
- similar requirements and tolerances as for isocratic elution have been agreed for gradient elution in LC;
- in gas chromatography, the conditions for adjustment of the column dimensions, injection volume, split ratio, injection port and transfer-line temperatures (the latter two being new for Ph. Eur.) have been harmonised;
- the adjustments for supercritical fluid chromatography have been deleted as this technique is not used in any Ph. Eur. monographs.
As was the case in the former version of general chapter 2.2.46, system sensitivity is to be checked on the basis of a minimum signal-to-noise ratio. This default requirement only applies to LC and GC tests (and not assays) for monographs that include a reporting threshold (or a disregard limit, in older monographs).
Local requirements, i.e. specific to an individual pharmacopoeia, will be placed between white diamonds (◊◊). For the Ph. Eur. chapter, these requirements include synonyms for retardation factors and guidance for determining the signal-to-noise ratio (e.g. solution to be used). Lastly, the term “relative retention time” or “RRT” will not be used in the Ph. Eur.