Persistant ghost peak????
<p> I wonder if someone could help us. We have had a few pump issues with our UPLC and the last time an engineer came he replaced the whole torpedo unit on primary pump B. He left the system in perfect working order (many thanks!). Unfortunately since then, we now have a strange peak in our chromatograms. It is not contamination in any of our solutions/mobile phases/sample solvent. The method is not heavily buffered, we use a gradient with ACN & 20mM potassium hexafluorophosphate pH 2.5. The sample solvent is a 50:50 mix of the mobile phase. We have performed wash after wash over several days, including the routine cleaning from sheet 715001908 REV. A. We have tried new columns, changed the sample syringe and needle and still it remains. Does anyone have any ideas of what it could be? Could it be something from the change of torpedo? Any help gratefully received.</p>