4 Replies Latest reply on Nov 1, 2018 8:12 AM by gchaplain

    Issue with GCD

    memfarmer

      After sitting in standby mode for awhile (days), when my GCD first turns on the filaments (after a 3 min solvent delay) there is immediately a broad peak that lasts perhaps 10-15 seconds, and it presents very different masses depending if you sample it at the beginning, middle or end. It is weaker on the subsequent samples, but never seems to go away altogether. I assume this is from junk accumulating on the filaments that then burns off. But why does it always seem to be there?

        • Re: Issue with GCD
          james_jenkins

          Hi memfarmer,

          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.

          Regards

          James

          • Re: Issue with GCD
            m4esti

            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

              • Re: Issue with GCD
                memfarmer

                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.

                Chuck Garner

                U of Memphis

                  • Re: Issue with GCD
                    gchaplain

                    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.