The current USP standard method, 231, for determining ‘heavy metals’ in pharmaceutical ingredients and products involves precipitating metal sulphides out of an aqueous solution, then visually comparing the colour of the test sample with that of a standard lead solution.
Although widely accepted and used in the pharmaceutical industry, these methods based on the intensity of the colour of sulphide precipitation are increasingly viewed to be non-specific, insensitive, time-consuming, and labour intensive and do not provide an adequate recovery of the elements being tested.
Because of these limitations the USP is proposing to replace test 231 by a method that uses inductively coupled plasma emission spectroscopy (ICP).
The ICP method will test for Al, Sb, As, Be, B, Cd, Cr, Co, Cu, In, Ir, Fe, Pb, Li, Mg, Mn, Hg, Mo, Ni, Os, Pd, Pt, Rh, Rb, Ru, Se, Sr, Tl, Sn, W and Zn.
The proposed revision will eliminate the specificity issue, provide greater sensitivity down to part-per-billion (ppb) levels and will evaluate the drug sample for an additional 21 elements.
Warwick Analytical Service, based on the University of Warwick Science Park in Coventry, UK, operates in an ISO 17025 and GMP compliant environment. It follows strict operating procedures, which ensures the delivery of top quality ICP data consistently.
The company is equipped with high-resolution ICP instrumentation and says it is able to resolve the most complex spectra and analyse even the most difficult samples.
Routine detection limits are low for most elements (typically <10ppb) and multi-element determinations can be achieved rapidly and precisely, the firm says.
