Our lab analyzes PAH compounds on a UV-VIS HPLC (EPA methods 610 and 8310). Lately I have been having problems getting the external check (second source) to pass. the recoveries for benzo-a-anthracene exceed the limits on both detectors. The continuing calibrations pass fine.

So far I have changed the solvents, the pump filter and used a second source from two different vials (one completely new), but still with the same results ?

Does anyone have more troubleshooting ideas and/or a solution ?

Thanks !