Chromatography Forum

I am observing unusual chromatographic artifacts on one of our Agilent 6890 GCs.

Instrument: Agilent 6890 GC

FID Detector

Direct Injection

Helium Carrier gas

Totalchrom software

The artifacts show up after multiple injections and continue to multiply. The initial injection is fine, and the problem goes away if the system sits idle for an extended period of time.

The problem persists across multiple different columns.

The problem persists across multiple different diluents (ACN and DMSO).

The problem does not persist when moved to another instrument (8890)

This exact method was run successfully on this instrument previously without issue.

See example here:

https://ibb.co/4Z8JgpSk

Here's an example of a chromatogram which includes a cool down back to initial temperatures. Notice that the artifacts re-appear at the end of the run when cooled back down to 40c:

https://ibb.co/G41pD3FL

I've never seen anything like this before. I'm at a loss as to what is happening or how to address it.

Septum, liner, any wool etc. in liner, retention gap, syringe -
have you cleaned silanized or replaced any/all of these items?
Each of these is a potential source of contamination and bleed.

Septum, liner, any wool etc. in liner, retention gap, syringe -
have you cleaned silanized or replaced any/all of these items?
Each of these is a potential source of contamination and bleed.

Yes, the septum, liner (including the glass wool), syringe and column were replaced.

The problem persists.

I have to say, I've been doing this stuff for nearly 40 years and I've never seen that either. My suspicion is that it's a noise problem. Have you tried taking your detector apart and cleaning all of the parts?

I have to say, I've been doing this stuff for nearly 40 years and I've never seen that either. My suspicion is that it's a noise problem. Have you tried taking your detector apart and cleaning all of the parts?

Right! I have been at this for nearly 20 years and it's new to me!

I have not cleaned the detector yet. However, the issue seems to be intermittent. We have run perfectly fine analyses on this machine prior to and after this. The GC is running right as I type this and those artifacts are not showing up. If it was a detector contamination issue, I would expect it to show up all the time.

But, I'm out of ideas, so I might just take the inlet and detector apart and clean them now.

Intermittent in the sense that it occurs intermittently only during cooldown, or it occurs intermittently randomly through the run?

Intermittent in the sense that it occurs intermittently only during cooldown, or it occurs intermittently randomly through the run?

Intermittent in the sense that full sequences can be run without the issue.

When it does appear, it appears with a seemingly regular pattern, that replicates more as additional injections are run. It's almost regular enough to make me think it's an electronic issue, but it does seem to be affected by oven temperature.

Occasional contaminant in sample vials? Do you rinse them with sample and dump a time or two before filling them?

Those look just like the distorted peaks that you get when there is liquid solvent on the column.

What do you mean by "direct injection"?

What column are you using, and what is its temperature programme, and flow rates.

Peter

This looks like normal chromatogram with working heart-cutting valve.

Your actual "valve" may be a crack in column, which "starts" at specific conditions. Try replace column.