I am curious to see if this carryover problem was ever resolved. I am currently running an HPLC method with 0.05% HFBA. The HFBA does show excellent separation for my parent compound and related substances as well as gives me adequate retention of an early eluter from the void volume. My problem is a carryover that I am seeing with the parent compound. I have isolated the carryover to the HPLC column. I have rinsed with 100% ACN (with 0.05% HFBA) and yet the carryover persists. I know it has to be the parent compound since when I change gradient, the carryover peak appears at the same retention time as the parent compound. If I switch over to TFA, then the problem goes away and I no longer have the carryover. However the TFA is not as good of a separator (2 carbon vs 4 carbon), the early eluter is much closer to the solvent front than I am comfortable with, and I see a much noisier baseline with the TFA. Any ideas of what might be happening or how to eliminate the carryover problem with the HFBA?