Concentration of impurity for linearity and accuracy must be decided based on release and shelf-life specification. Here is the video which explains you how...
Generally, qualification threshold , monograph will guide us on impurity limits. As a general practice, you may have stringent limit for impurities at release to accommodate their instability till shelf life. Shelf life limit must be inline with qualification threshold , monograph requirements
-You can use Accelerated Stability sample with maximum level of impurities -Or near expiry RLD sample -you can go for FD study -Light exposure if the sample is light sensitive etc.
