I have been having difficulty with a related substance method transfer for a 60 mg pharmaceutical tablet. My values for % diastereomers relative to the parent peak are about half of the client's values. The 60 mg tablet is the same formulation but twice as large as a 30 mg tablet which transfered with no problems. The only difference between the two methods is that the 60 mg method does not require centrifuging the sample prior to final filtration. When the client takes some of our sample tablets, uses our draft method, with the same model HPLC system and column that we use, they get twice the % diastereomer peak area that we do. Any dilution or calculation error has been ruled out, as has any system problem since concurrent analysis of 30 mg sample produced consistent results (the 30 and 60 mg samples are prepared to the same concentration) Any ideas?

Have you tried your solutions on your clients kit and vice versa - soulds like an instrument problem rather than a method problem- I assume all other aspects of SST have been examined?

regards