Hello to all. My department is trying to standardize the way we report levels of impurities in HPLC methods. I have a couple of questions. What should we set as a minimum area % for reporting known and unknown impurities? Some of our methods utilize 0.02% others 0.05% for minimum levels. (This question arises out of a stability frame of mind -- if peaks grow we want to know from what level and how fast...) Also, in instances where an impurity may be present in one sample prep but not in the other, how do you report? (Do you recommend reporting as NMT amount found in the first injection? Do you average the determined amount in first result against whatever you set as your minimum reporting level? or Do you average against zero?) Thanks in advance for your comments.