The baseline jumps by 10 pA at once

[Yuliia]

Good day to all,

I work with the Agilent 7890A. We plan to determine fatty acids in blood plasma. I am not an expert in this matter, so I have to study everything practically from scratch. Unfortunately, no one works on the device and could suggest something. Therefore, I only hope for help on the forum.
A few months ago, problems with the baseline suddenly began. Every time after turning off the device, the next time it was turned on, it rose by 10 pA. At first, it was possible to return it after half a day of operation of the device in the stabilization and column conditioning mode. But over time, this process became more and more prolonged. I stopped turning off the device on weekends and leaving it in sleep mode. Again, this helped for some time, but then everything began to worsen again. What is typical is that every 45 minutes such steps are observed on the baseline.

https://ibb.co/7trzKwb

The last time, the baseline suddenly jumped by 10 pA right during the analysis. The baseline has stopped falling below 20 altogether; it stays at 20.5-21 all the time. This is the problem, and I don’t know what is causing it...

https://ibb.co/QQXvgf0

[DR]

Please provide more information about your method and especially your sample prep.

Have you tried a clean liner?

Blood plasma is not a nice thing to be injecting into a GC. I'm certain you're doing things to clean up the samples, but it may be that you're just polluting one (or both) ends of the column over time.

Assuming it's a capillary column, do things improve if you trim either end?
Please try this if you have not yet done so.

[Yuliia]

Initially, we used this method.
Column: Agilent J&W DB-FATWAX Ultra Inert, 30 m × 0.25 mm, 0.25 μm
Carrier gas: Helium, constant flow mode. 30 cm/s
Inlet: 250 °C, split ratio 50:1
Oven:
40 °C (2 minutes),
55 °C/min to 171 °C (25 minutes),
10 °C/min to 215 °C (25 minutes)
FID: 280 °C, Hydrogen: 40 mL/min
Air: 400 mL/min
Make-up gas: 25 mL/min

But later problems with the peak release time began - it began to shift further and further. Therefore, the method was slightly modified (add a change in the flow)

Ramped flow: 1.4 ml/min (25 min)
0.2 ml/min to 1.8 (30 min).

As for the sample preparation method, we are looking for the most effective one, so they are changing all the time.
One of the latest is extraction using the Bligh and Dyer method, and then derivatization with BF3/MeOH.

[Yuliia]

We have already changed the liner and septum, cleaned the FID, cut the ends of the column several times. Nothing has changed((

[antonk]

Blood plasma contains huge amount of proteins >1000 DA.

https://www.empbiotech.com/chromatograp ... tionation/

It looks like you periodically see the peaks of these components.

What I can propose - centrifugation of your samples or gel-separation.
Or derivatize fatty acids and use headspace.

[Yuliia]

Blood plasma contains huge amount of proteins >1000 DA.

https://www.empbiotech.com/chromatograp ... tionation/

It looks like you periodically see the peaks of these components.

What I can propose - centrifugation of your samples or gel-separation.
Or derivatize fatty acids and use headspace.

Sorry, I didn't quite understand where you saw peaks of proteins?

I wrote above that we perform lipid extraction using the Bligh and Dyer method then carry out derivatization with BF3/MeOH.
The last chromatogram with a sharp baseline jump was from a sample with a different derivatization method (by MeONa).

Maybe I didn't write it clearly enough. The baseline rises every time the device is turned on after sleep mode. And these "steps" that appear every 45 minutes appear all the time when the device is just turned on and no analysis is carried out.

[Yuliia]

hello, Air for FID is compressor or gas cylinder. I see this problem when compressor start run and end, and compressor have bad moisture filter.

Thank you very much! We really haven't checked this.