Unexpected base line (GC FID)

Hello everyone!! I am new to this forum

I have been given an Agilent GC/FID 7890B and asked to set a fatty acid analysis method.

The thing is that I have been having problems with the base line recently and since I am new to GC chromatography I don't know what is causing it and how to solve it.

Column: HP-88 60 m x 0,25 mm, 0,2 µm ; Oven inicial temp: 125 ºC ; Oven max temp: 220 ºC ; Carrier gas: He ; Detector: FID 260 ºC ; Sample solvent: n-Hexane

If there is anything else important that I should mention let me know!

So, a month ago this is how a run of a 10 ppm 37-FAME sample would look like:

And this is how a 10 ppm 37-FAME sample looks like right now:

And if this is any helpful here is an image of a Blank sample on the same run as the previous sample:

I would appreciate any help or criticism !!

Parents
  • Adrian - do you have a compressor attached to the air line on your FID? I've seen similar traces to the middle one when a compressor is making life hard for the FID's EPC to balance pressure going to the FID's flame. If you've got a cylinder air then it might be worth switching to that. Also, check your gas purity and gas trap situation. 17pA is pretty normal as an FID baseline but if it's moving around you might have some contamination too.

Reply
  • Adrian - do you have a compressor attached to the air line on your FID? I've seen similar traces to the middle one when a compressor is making life hard for the FID's EPC to balance pressure going to the FID's flame. If you've got a cylinder air then it might be worth switching to that. Also, check your gas purity and gas trap situation. 17pA is pretty normal as an FID baseline but if it's moving around you might have some contamination too.

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