Hi people, I am currently using Waters Acquity UPLC coupled with TQS to study Plasmalogen (both phosphatidylcholine and phosphatidylethanolamine) and I am experiencing carryover issues when doing target profiling (MRM), such problem did not exist in global run. I've changed to a new column and the very first run had appearances of the carryover from previous plasmalogen samples, so i doubt the problem is with the column. Problem doesnt get any better despite washing ion source of MS.

Intensity decreased over blank injections, and peaks still appear when performed zero-volume injection.

100% ACN is used as strong wash and 95% H2O + 5% ACN is used as weak wash. Strong needle wash consists of 100% IPA and Weak needle wash consists of 90%H2O + 10% ACN. Mobile phase A is 40% H2O + 40% Methanol + 10% ACN while Mobile Phase B is 100% IPA. Other lipid compound studies uses same solvent composition and did not have carryover issue. So I think the problem is that the solvents are not that effective in getting rid of plasmalogen?

The column I am using now is Waters Acquity CSH C18 Microflow column, flow rate is set at 0.1mL/min and temp at 45 dC.

Not sure the problem lies with sample loop or unsuitable wash solvent? Hope some experts here can give me some suggestions.

Thanks in advance!