Replacement of the wet chemistry “heavy metals” limit tests with more modern analytical methodology and conformance to new and specific limits for individual elements was a dramatic, although anticipated, change in the regulation.
The ICH recognized that prior to the Q3D Guidance, regulation of elemental impurities fell under Guideline Q3A for inorganic impurities. Existing pharmacopoeial procedures included the Heavy Metals test, Residue on Ignition/Sulfated Ash test and other wet chemistry tests. The problem with these procedures was that they were non-specific and were never intended to detect the low-level residual metal catalysts and reagents used in some modern synthetic processes. In addition, the acceptance criteria were based upon historical precedent and, although risk factors for metal contamination had changed significantly throughout the 20th century, the existing limits had not changed accordingly and had little toxological basis.