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Different methods give different answers when calculating limits for impurities. The prediction interval method may be the best option.
Regulations require drug manufacturers determine the detection limit (DL) and quantitation limit (QL) of impurities in APIs and drug products. There are multiple ways of doing so, some of which are described in the International Conference on Harmonisation (ICH) guideline, ICH Q2 (R1) Validation of Analytical Procedures: Text and Methodology. Primarily, these methods are based upon the statistical uncertainties from a linear least squares regression calibration curve. However, different calculation methods give different answers. The following describes an example and a recommended best practice method.
Chris Burgess is managing director, Burgess Analytical Consultancy Limited, Barnard Castle, Co Durham, UK.
Volume 45, Number 11
When referring to this article, please cite it as C. Burgess, “Detecting and Determining Quantitation Limits for Impurities,” Pharmaceutical Technology 45 (11) 2021.