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GC-FID Mineral oil Baseline
Posted: Mon Apr 15, 2024 6:06 am
by CrisTheChemist
Hi Chromatographers,
I have a trouble with GC-FID analysis of mineral oils C10-C40 in water, soils, waste (ISO 16703). It is an instrumental problem not related to sample type or extraction.
I have been doing this analysis for many years, but now I have this problem that I have never seen before.
Sometimes the chromatogram of the blank or a std or a sample shows a negative band that goes below the starting level of chromatogram hence I can not integrate the classic large peak at the baseline.
I have just changed the column, the liner, the jet assy of the FID, but some days the problems doesn't appear, whereas other days the problem exist.
Do you have some similar experience?
I can share some chromatograms but I need your email address.
Really thank you
Re: GC-FID Mineral oil Baseline
Posted: Wed Nov 20, 2024 12:59 am
by propertylilac
CrisTheChemist wrote: ↑Mon Apr 15, 2024 6:06 am
Hi Chromatographers,
I have a trouble with GC-FID analysis of mineral oils C
10-C
40 in water, soils, waste (ISO 16703). It is an instrumental problem not related to sample type or extraction.
I have been doing this analysis for many years, but now I have this problem that I have never seen before.
Sometimes the chromatogram of the blank or a std or a sample shows a negative band that goes below the starting level of chromatogram hence I can not integrate the classic large peak at the baseline.
I have just changed the column, the liner, the jet assy of the FID, but some days the problems doesn't appear, whereas other days the problem exist.
Do you have some similar experience?
I can share some chromatograms but I need your email address.
Really thank you
Check FID flame stability and gas flow.
Ensure new GC column is properly conditioned.
Check for leaks at column connections and column cleanliness.
Check injector temperature and clean syringe.
Check for electronic noise or signal power stability.
Re: GC-FID Mineral oil Baseline
Posted: Thu Nov 21, 2024 8:23 am
by Benzene
Hello CrisTheChemist!
In the early 1980s, I experienced problems with negative signals or unstable baselines when using a high-resolution gas chromatograph (Carlo Erba Instruments, Model HRGC 5300 Mega Series), one of the best on the market at the time. Today it would be considered prehistoric.
Drawing from my experience in the GC laboratory, I'd like to offer the following advice:
- You must be sure that the gas flow rate is constant and that the gas is clean and free of contaminants. I encountered an issue with a nearly empty gas cylinder. I replaced it, and the problem disappeared.
Prepare the sample, ensuring it is not contaminated and selecting the optimal concentrations to avoid overloading the detector.
Check with your electrician to ensure the gas chromatograph is properly grounded using a Megger, and verify that there are no voltage fluctuations..According to the user's manual, I had a tolerance of +/- 2% for the power supply, which specified 230V at 50Hz.
To optimize the baseline settings and minimize electromagnetic interference, you'll need to make adjustments. Unfortunately, I'm not familiar with your specific laboratory setup, so I won't be able to provide personalized guidance.However, I would advise against bringing mobile phones near the GC.
To pinpoint the exact moment of the defect, analyse the chromatograms using standardised samples.
Monitor the temperature, humidity, and mechanical vibrations in the lab.
By applying these tips, you should be able to resolve the issues.
Good luck with your work! 
Krgds,
Benzene
Re: GC-FID Mineral oil Baseline
Posted: Thu Nov 28, 2024 1:20 am
by Zachary Warren
CrisTheChemist wrote: ↑Mon Apr 15, 2024 6:06 am
Hi Chromatographers,
I have a trouble with GC-FID analysis of mineral oils C
10-C
40 in water, soils, waste (ISO 16703). It is an instrumental problem not related to sample type or extraction.
I have been doing this analysis for many years, but now I have this problem that I have never seen before.
Sometimes the chromatogram of the blank or a std or a sample shows a negative band that goes below the starting level of chromatogram hence I can not integrate the classic large peak at the baseline.
I have just changed the column, the liner, the jet assy of the FID, but some days the problems doesn't appear, whereas other days the problem exist.
Do you have some similar experience?
I can share some chromatograms but I need your email address.
Really thank you
Verify the gas flow and flame stability of the FID. Make that the new GC column is conditioned correctly. Verify the cleanliness of the columns and for leaks at the connectors.