This sounds more like you are catching the end of a solvent peak, try lengthening the solvent delay to 3.5 minutes as an experiment.
If is the same method you have been using. Might need to trim off column and do inlet maint. Like James said some how solvent inject peak is being retained, might be residue holding it up.
Mitch: I did a blank run with no injection made, and the peak was still there. I’ve enclosed a scan of it and the MS it gives. Notice how it rises up at first, rather than dropping off continually (like retained solvent would do). Do you recognize the masses at all? I wonder if it could be contamination from vacuum pump (or diffusion pump) oil, or maybe PFK if the solenoid isn’t closing securely? Thanks.
U of Memphis
If it is an MS problem it should be there throughout the entire run, so you would see it across the whole chromatogram. However like James and Mitch state, it is likely carry over in the inlet.
What solvents do you typically inject with and what is the main analyte you look for? Because it comes off the column so early would suggest a light compound with minimal column retention.
I would check under the septum for any residue (already changed the liner), inspect and change the gold seal, potentially change the split vent trap, and if they don't work, I'd even clean the split vent line with a volatile solvent then evaporate it off.
have you done any inlet management? I would recc removing and flushing split lne and scrubbing inlet