LOQ from [ ] to % area (Disregard areas)

[androzmm]

I'm currently validating a USP method for impurities, I spiked certain know impurity and based on S.D. and slope I got 0.020mg/mL and 0.016 mg/mL in a second HPLC so my avg was 0.018mg/mL of concentration, the recovery was within 80% to 120%, how can I extrapolate this value to % of areas so I can describe what percentage of the impurity can be disregarded if it is bellow that percentage?

[DR]

First off, you want an occasional peak whose area will correspond to a little less than your LOQ. This keeps reviewers and auditors happy. That said, it depends on how your company sets LOQs and possibly on any relative response factors that are in play.

Typically, I look at the LOQ for unknowns, look at the main peak area for samples and multiply that by the LOQ, then I rule out any peaks that are not at least ~75% of that.