Methods of Impurities Calculation
Methods of Impurities Calculation According to ICH guidelines impurities can be broadly classified into three categories as Organic Impurities, Inorganic Impurities and Residual Solvents. Related substances are defined as impurities derived from the drug substance and therefore not including impurities from excipients. Related substances include degradation products, synthetic impurities of drug substance and manufacturing process impurities from the drug product. Various concepts are used for the quantitation of impurities which are elaborated in this article. The following calculation approaches can be used: 1. External standard approach against quantitative RS for impurities. In this method quantitation is performed against an external standard of impurity itself. An external standard also serves as positive impurity peak identification rather than relying on relative retention times which are subject to reliability. Quantitation of impurities using this method pr