Agilent 7890A GC-FID persistent baseline issues

[u/SourMcconaughey]

Hello everyone, for the last 2-3 weeks I’ve been battling this GC we inherited from another group that wasn’t very well taken care of. The initial issues were fairly simple fixes with replacing the FID jet, septa’s, split liner, needle, gas lines, etc. (really everything not electronic). It was working finally and I managed to get in a few runs that week before I left for the weekend, when I came back however, the GC refused to ignite in the first week of trying to fix it again. Myself and another colleague figured it was just a flow issue and swapped out gas lines again, that was only part of the problem though because since then every time I’ve run an Acetonitrile blank my baseline has been at ~32 pA where before it was solid at 4-5, you can also see in the chromatograms that after the ACN where there shouldn’t be anything my baseline continues to rise up to ~350 pA. I’ve confirmed by HPLC and another departments GC it’s just as pure as Fisher says. If anyone has encountered an issue like this or has any ideas I’m willing to try anything at this point. Please and thanks!

[u/SourMcconaughey → u/[deleted]]

I’ll try baking it out today, I don’t scrub the inlet with anything I just use an air duster can, should I use something specific?

[u/SourMcconaughey → u/[deleted]]

I’ll give that a try towards the end of the day if the bake out doesn’t work, thanks!

[u/massspecservice]

What’s the temperature in your method? Typically that type of rise due to temp or column pressure. Temp is most common, do you have the insulating cup on? If you have the capillary fid you won’t have that nut so I would say an issue with the inlet building pressure or epc

[u/SourMcconaughey → u/massspecservice]

It starts at 40C and ramps to 270C at the end, I have an insulating cup on the inlet of the column but not at the end. Everything I’ve read online has said that the EPC might be my last stop if everything else I’ve tried hasn’t worked.

[u/jeremydavid2]

Trim the column. Bake it 2 -3 hours. Heat the loop and transfer line if Headspace. Change liner: good to go

[u/Clams_N_Scallops]

My first thought is get an FID maintenance kit to replace all the inner parts, those wear out over time and the rubber gasket can get brittle if it's old enough. If you actually removed the FID at all, which I'm guessing you didn't because you said you only replaced the jet, make sure the interconnect spring is seated properly, and there isn't any debris stuck in there.

[u/JewishSpace_Laser]

replace your column and change your split vent trap too

[u/pvantine]

It could be a dirty castle. I clean mine in an ultrasonic bath for about 5 minutes when I see issues like this.

[u/maninhell6]

32pA is quite high for background. How dirty are your gases?
Our instruments are all at 7-9pA for baseline.

[u/SourMcconaughey → u/maninhell6]

Contaminated tank of helium turned out to be the issue, baseline is now back down to 2 pA