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 !!

  • Hi

    What is inlet temperature?

    Without any injection, baseline okay or not..

  • How old is column?

    Did you check baseline with new column...

  • Hi Adrian,

    Please try following these step

    1. Injector: you check liner (change silica wood or replace a new one)

    2. Detector: Remove the column from detector, use a ferrule no hole insert to detector and run without sample.

    + If base line is good: condition your column ( 50C hold 15min, increase 5C/min to 240C hold 60min, decrease 5C/min to 50C hold 10min- end.

    + If base line still bad: cleaned detector is necessary.


  • 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.

  • Hi did any of these recommendations help solve your problem?  

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