Chromatography Forum

Hi Everyone,

Periodically, I see phantom peaks that are uncharacteristic of any other peaks I get when I run a sample. They are very thin and narrow and then FID signal goes to zero before returning to baseline signal.

I started to condition my column, and received a peak, and copied image below. These peaks sometimes occur during a run and then affect the integration due to the signal going to zero after that narrow peak.

Does anyone have experience with this, and can offer an explanation why this is occurring and how I may prevent it. I thought perhaps it may be dust in air settling in detector, or detector may be a bit dirty or there's an overlooked wrong setting of detector. My air is set at 350 ml/min and hydrogen at 35 ml/min, and FID is set at 270 C, so I am not sure what else could cause this problem. Helium carrier is 1.2 ml/min at detector and make-up gas is on at about 10 ml/min.

These peaks do not happen very often, but can ruin a run when they do, and thus can be an annoyance.

Thanks in advance for your help,
Carvone

Hello
The peak is very thin. I think it could be a spike, caused by a particle eluting through the FID.

Hi

Flows seems accurate.

Have you tried replacing/cleaning the jet and blowing air/nitrogen from under fid up through it while jet is removed? (you may be surprised how much ferrule resiudes that can be found).

Thank you Francesc and Krickos,

I should have mentioned even though these mystery peaks occur rarely, they started after I switched FID jet for smaller ID column. So it's possible residue was stirred up during the transfer. I will reinstall jet and blow out as suggested.

It's occurring less frequently now possibly since any residue stirred up during jet change may be baked out.

I am still curious why the detector signal went to zero after the peak almost as if detector shut off for a split second then started again.

Do either of you know why this happens? Have you seen that before?

Your thoughts are much appreciated,
Carvone

I already had these negative peaks once. But after a certain time they went away, we concluded it was related with the gas lines, since they occured when gas bottles were changed. It was visible in all our instruments with FID that were on-line at that moment (MS were ok), so we suspected it was something in the hydrogen or air lines (or it was a air bubble in the hydrogen line or some kind of mineral oil that was not trapped in filter and that overloaded the detector)!
Besides the jet, did you connect a new gas bottle recently to your lines?
Regards,
At_om

Hi At_om,

Yes I did replace the compressed air not too long ago -- not at exact same time as changing the jet but thereabouts. Good to know the peaks went away.

kind regards,
Carvone

Have you installed Hc's traps on the air, fuel and carrier lines. I already have seen such kind of phantom peak and it was coming from hydrocarbons in my air.
I can supply to you some traps for such application if necessary.

Are you using a PLOT column? I've seen this when the column particles break loose and pass through the FID.

No, it is a simple DB-5 capillary column. Also, I do already have traps on the gas lines.

Thanks.

Have you tried to turn off the FID to trend only the baseline? It may comes from an electrical problem or noise caused by....
Going in this direction you will isolate the source of the problem.

If the spike disapears, it means the problem comes from a chemical reaction or the detector. I would now suspect the carrier gas again. I would suggest to install a gas purifier on the carrier line. I can propose to you a good product for this application. (shoot me an email at instrumentseoul@gmail.com)
Also, it may comes from a bad cleaning of the FID detector.