With the First Supplement to USP 30/2007, the General Chapter <11> USP Reference Standards was revised. Up till now, in case of USP Reference Standards used in quantitative applications, the purity was always supposed to be 100% if no other percentage was indicated (mostly after the standard had been dried). The new Chapter <11> now includes a "calculation value". From now on, reference standards used in assays will have a calculation value with three significant figures, whereas Reference Standards for limit tests will be labelled with two significant figures.

The calculation value of a Reference Standard used in quantitative applications is determined by means of a collaborative study. Here, the method of choice is a mass balance analysis using independently determined components, such as moisture, solvent residues, or inorganic residues.

Older lots of USP Reference Standards will not be re-labelled with a calculation value. In this case, users should continue to apply the purity default value of 100%.

The calculation values will not be assigned to standards used in qualitative applications. Unfortunately, there will still be no certificates of analysis for the Reference Standards. The First Supplement to USP 30 comes into force on 1 August 2007.

Author:
Dr Günter Brendelberger
On behalf of the European Compliance Academy (ECA)