Method validation is an essential step in confirming by examination and providing objective evidence that the method used is suitable.
In the context of PE 2.4.20, you are looking to analyze metal residues from catalysts or reagents in pharmaceutical products
In addition, as of January 2018, the guidelines set forth in the ICH Q3D: Elemental Impurities guideline became applicable to all human drugs on the market. In addition, analytical methods can be developed using the general chapter Determination of Residues of Catalysts or Metal Reagents 2.4.20 (Figure 8: Extract from Ph. Eur. 8th Edition – Volume I).