Annoying regular ghost peaks?

Question

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?

THANX

dmarchini · Accepted Answer

Thanx guys, I have

-cleaned the inlet section with cotton swabs and isopropyl alcohol (body of injector/reducing nut)

-replaced the split vent cartridge (it was like 5 years old..)

-replaced liner and septum using advanced green septa

-thermal heated the column then

but...I found ferrules pieces between the gold seal and the liner!

Now everything is good and my baseline is perfect.

Thanx guys!

shawntravis · Answer

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.

jasonellis · Answer

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

james_jenkins · Answer

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

Annoying regular ghost peaks?

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