10 Replies Latest reply on Jun 1, 2018 8:33 AM by bigbear

    Annoying regular ghost peaks?

    dmarchini

      Hi guys, I'm experiencing regular times ghost peaks starting at 120°C to 295°C.....my setup is GC-FID 6890, Low pressure drop, Ultra Inert Liner with glass wool, column HP1 widebore.....

       

      I have cutted the inj/det 5 inches of column, heated at 295°C with 1mL/min Nitrogen flow, changed the liner...but nothing has changed.

       

      The column is new, I only injected few samples of "ketones" in acetone.

       

      The analysis below is a vial of HEXANE; I have those regular ghost peaks injecting acetone or acetonitrile as well.

       

      What I have to do?ghostpeaks.jpg

       

      THANX

        • Re: Annoying regular ghost peaks?
          james_jenkins

          Hi dmarchini,

          I did some rough calculations , can you confirm the head pressure on the inlet at the above conditions? To me, after some rough calculations,  it seems like it would be too low for efficient sample transfer. A complete listing of your method would be helpful in understanding what is happening.

          Regards

          James

            • Re: Annoying regular ghost peaks?
              dmarchini

              Thanx James, here we go!

               

              gc9b.jpg

                • Re: Annoying regular ghost peaks?
                  james_jenkins

                  Can we get the oven program as well? Have you tried an injection with out injecting, essentially a blank run? You can remove the syringe from the injector and perform a run. This removes the effect of solvent and needle from the inlet. A test to see if we still get the little peaks.

                    • Re: Annoying regular ghost peaks?
                      dmarchini

                      Hello James, in attachment you can see the temp parameters: I experience ghost peaks also in the blank injection.

                      maybe I have yet corrupted the column phase?!

                      GC9C.jpg

                        • Re: Annoying regular ghost peaks?
                          james_jenkins

                          The peaks are very small as well as the signal response.I would try thermally conditioning the column for an hour or more at 10 degrees above the max of your run and try again.

                          James

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                          • Re: Annoying regular ghost peaks?
                            shawntravis

                            I agree with james_jenkins that an easy first step is to heat up the column for a bit and thereafter acquire another no injection run.  After that, you may also try multiple solvent injections to "rinse" the inlet and column (start with something like 10 solvent runs and then make another no injection run afterwards to reevaluate how big the peaks still are to decide whether to continue running more solvent or move onto changing parts).

                             

                            Please confirm that your blank run was acquired without a syringe in place as this will change the troubleshooting path if there was an actual injection made.

                             

                            Assuming no injection was made, as a next step, I would advise performing inlet maintenance on your SSL inlet (replace septum, inlet liner with oring and gold seal at the bottom of the inlet).  There could be chunks of septum material in the liner or sitting on top of the gold seal that have retained sample material from previous injections.  This sample material is then included in any runs you make.  This would typically be seen as increased baseline not peaks because this material should be added to the carrier gas stream all the time at the same rate and not intermittently as an injection would be, but replacing those items is easier compared to the next steps.  If the initial maintenance does not work, then expand the maintenance to include swabbing out with solvent the bottom portion of the inlet where the liner goes (gold seal and its reducing nut removed for this step) as well as cleaning or replacing the split vent line and replacing the split vent filter, then run another no injection.

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                    • Re: Annoying regular ghost peaks?
                      jasonellis

                      Ghost peaks that elute in a series like this are generally related to septum bleed. The regularly spaced peaks are indicative of a homologous series of siloxanes bleeding off of the silicone septa material. This could be coming from the septum itself or could be from septum chunks in the inlet and/or liner.

                       

                      What inlet septa material do you use? I recommend the Agilent Advanced Green or BTO septa.

                       

                      Have you tried changing the liner and gold inlet seal?

                       

                      Best regards,

                      Jason

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