text.skipToContent text.skipToNavigation

No assay value mentioned for a pharmacopoeial reference standard?

And the right answer is: It depends on the situation!

We know that there is still the “rumour” out in the analytical community, that you can take the assay of compendial standards as 100% when nothing is written on the label.

The reason for this rumour is a misinterpretation of a passage in USP's General Notices, which says under clause 5.80 [3]:

‘Unless a reference standard label bears a specific potency or content, assume the reference standard is 100.0% pure in the official application.’

The word ‘official’ is overseen by many users. A standard, which is solely used for identification in the compendium, is 100% pure (or in this case suitable) for that single official identification purpose. But the assay could not be taken as 100% for an unofficial quantification purpose outside the pharmacopoeia as well.

The EDQM does not apply the “no-assay-then-100%-rule” to their API reference standards, but to a small number of their impurity standards. They state the following in their FAQs:

‘Where can I find the assigned content of a Chemical Reference Standard used in an assay? 
The assigned content of a CRS assay is provided in the leaflet available ...
If a CRS has no assigned content, this should in no case be interpreted as if the content were 100 per cent. For assay purposes, the content explicitly assigned must be used and in no case should the user interpret this as if the content were 100 per cent.

However, when an impurity reference standard is used in a related substances test for the control of an impurity and if no assigned content is indicated, the purity of the reference standard, for the purpose of this estimation, is considered to be 100 per cent.’

So, when in doubt, send us an email to pharma.tech@lgcgroup.com, and we would be happy to help!





Refine your


Online Ordering made easy


Sign up to our email newsletter



Punchout session timeout warning

Your punchout session will expire in 1 min 59 sec.

Select "Continue session" to extend your session.