Chromatography Forum

I've been having some issues with my 6850 GC which have me stumped. This is what chromatograms looked like just before the problem occured
method is FAMES

July 17th

sample

another sample
July 25th

standards

after the problem occured the chromatograms started to look like this

September 1st

sample

standard

Replaced split vent trap (new trap looks slightly different to old), baked out column

September 10th

sample

another sample

another sample

replaced H2 hydrocarbon trap, cleaned inlet with brush and methanol, removed copper tube going off to split vent and cleaned with methanol

Today

sample

any ideas what else to try? I've done what Agilent recommended they have no other suggestions apart from paying an engineer to fix it.
one other thing that was suggested to me which I haven't tried yet is cleaning of the FID jet

Is your syringe OK ? (compare solvent peaks).
Clean FID jet.
Check gas flows through FID.

You have dramatic loss of sensitivity and a huge in increase in retention time (presuming that the peaks that do appear are the same substances on before and after chromatograms.

Check that the gas flow through the column is what it is supposed to be by injecting a plug of lighter gas and measuring how long it takes to elute.

Check for leaks with a leak seeker, not with any onboard GC diagnostics.

Have you changed liners and gold seal as part of your troubleshooting ?

Is your oven really following the right temperature programme ?

Peter

Hello

I'd check:

1.Leak test for inlet
2.Check syringe (do simple pressure test- fill syringe with methanol and put needle to used septa to see if there is resistance)
3.Inject methanol (about 3ul to see if peak comes out)
4. check detector gases flows
5. check if column is not broken (somewhere on metal cage)
6. check distance for column in inlet (4mm) and FID (about 1-2mm below jet)

Regards

Tomasz Kubowicz

Hello

I'd check:

1.Leak test for inlet
2.Check syringe (do simple pressure test- fill syringe with methanol and put needle to used septa to see if there is resistance)
3.Inject methanol (about 3ul to see if peak comes out)
4. check detector gases flows
5. check if column is not broken (somewhere on metal cage)
6. check distance for column in inlet (4mm) and FID (about 1-2mm below jet)

Regards

Tomasz Kubowicz

This all looks sensible. The last time I saw an issue like this I found that the column had been accidently cooked and most of the column destroyed. Try swapping to another column

I'd be happy to see chromatogram parts from the injection to 5 min.

These after a problem occured and those before.

Hello

I'd check:

1.Leak test for inlet
2.Check syringe (do simple pressure test- fill syringe with methanol and put needle to used septa to see if there is resistance)
3.Inject methanol (about 3ul to see if peak comes out)
4. check detector gases flows
5. check if column is not broken (somewhere on metal cage)
6. check distance for column in inlet (4mm) and FID (about 1-2mm below jet)

Regards

Tomasz Kubowicz

Hi Tomasz, thanks for your reply

1. Do you mean test the inlet with a leak detector?
2. When you say put needle to used septa to see if there's resistance, I don't understand what to do. Inject into a used septa?
4. On the software the total inlet flow is 0.1-0.3 below the setpoint, H2 pressure is also always below setpoint. It seems the column nut is a little bent causing the column to not interface with the inlet properly. Maybe this is the cause?
5. How do I know if it's broken?
6. In the Agilent videos they say it should be 6-8mm but I've also heard 4-6mm

This all makes it sound much more likely that you have a massive leak at the column connection to the inlet. You must check for leaks there with a leak seeker - you can get one from any of the instrument companies, Supelco, Restek etc. In the meantime check the retention time of lighter gas if you have not done so already.

Peter