Gas chromatography-spike in baseline

[mandytan]

I conducted a Gas Chromatography experiment using Flame Ionisation Detector (FID).A capillary column was used;injection volume 1uL; split flow1
1)Blank
2) Standard
3) Sample
4)Blank
5)Standard
The above was injected into the system.

In 2)Standard chromatogram,a sharp, thin peak was observed between the 2 principal peaks. This peak had area count of less than 100.
This sharp peak was also seen in 4)Blank.

However, this sharp peak was not present in 5)Standard chromatogram.
Can you suggest a reason for this sharp spike/peak seen in 2) and 4)?

[Don_Hilton]

It could be from carbon in the FID. Examination of the jet may not be a bad idea.

[mandytan]

Hi Don,
Can you kindly advise how to tell if the jet is the reason for this "peak"?
Since this "peak" does not co-elute with other peaks, can we say that the sample results can be accepted? The integrity of the results will not be compromised as we will exclude the integration of this "peak" in the chromatograms?

Thanks.

[chromatographer1]

A spike is an upset in the current flow in the detector. It can be electronic in source, or it can be caused in a FID by a particle (a loosen chemical deposit, a chunk of septum, or a salt particle entering between the two electrodes of the detector causing a disturbance in the current flow. It can be caused by electrical surges in your power supply as well. A loose connection to your data system will also cause such problems.

best wishes,

Rod

[Don_Hilton]

I'm not sure that you can ever "know" that carbon (or other junk) in the jet was the cause. If you can see stuff collected on the jet, it may be the case. If you clean or replace the jet and there are no more spikes, it is likely that you fixed the problem.

Unless you know what happened, the result is at least to some degree suspect. If the spike is an electrical connection issue, can you say for sure that there was no change in attenuation of the signal by the loose connection was the same before and after the spike?

The safest is to check connections, be sure you have a clean jet, and inject again. Depending on what you are doing, you may be able to make a judgment to use the results you obtained. But, you have to know that you know enought to make a good call.

[Hornet]

Like already said it's either the jet contaminated by carbon/stationary phase or an electronic signal, probably coming from the electrometer cable.
Try to move the cable while running a blank and see if it happens again, when they get old/partially damaged by heat they make spikes even with normal instrument vibrations, it happened to me in the past and i solved it by changing the cable.
Also it would be useful to know the instrument age, the column type/age/sample it runs/temperatures and if the spike happened at the same RT/temperature or it was random.

Spikes aren't a big problem unless they are many and they happen often, if the instrument works correctly i wouldn't touch it for just some isolated spike.

[Consumer Products Guy]

I'd say 95% of the spikes we see here are within the first 2 hours of installing a column, or installing column into FID.

Doesn't matter if new or previously-used column.

[edmgc7788]

I think it might be the liner or septa leaking. From your question, the spike peak doesn't show in 3) and 5).It is not always there. I think you check your liner. I use FID, sometimes, if there are spike peak in my samples i will see there is dark chunk in the liner.
thanks

[CMDR2279]

I think it might be the liner or septa leaking. From your question, the spike peak doesn't show in 3) and 5).It is not always there. I think you check your liner. I use FID, sometimes, if there are spike peak in my samples i will see there is dark chunk in the liner.
thanks

Agreed. Often I see spikes in blanks and it is- in my case- usually a dirty liner. I change the liner often, run a series of blanks and bake out the oven. It usually resolves the issues.

Best of luck,

Cary