How can I reduce Tailing for Atomoxetine, Reboxetine, and Maprotiline in a Reversed Phase C18 HPLC method? I am using a pH 4 Phosphate/Acetic Acid Buffer.
Atomoxetine, Reboxetine, and Maprotiline all have Amine Groups. Standard C18 phases may have Residual Silanols on the surface which can interact Electrostatically with the Amines from these analytes. These interactions are one of the most common causes of Tailing.
Suggestion: Try operating at a lower pH where these Silanols are not Ionized. Use 0.1% Formic Acid in the Mobile Phase instead of the pH 4 Phosphate/Acetic Acid Buffer.
As for the Column, the Cogent Bidentate C18™ Column would be a good choice. Unlike conventional C18 Phases, the Cogent Bidentate C18™ is based on Cogent TYPE-C Silica™ which is virtually free of residual Silanols. Therefore, the adverse Silanolic Interactions that may cause Tailing can be avoided altogether.