FID signal loss

[SuperChemie]

I am seeing my FID flame go out and then reignite during a run. I sonicated the jet in Methanol and then did not have the problem for a few runs but then it returned. The jet is not new so perhaps it just needs replacing?

Anyone had this problem before?

[img]http://oi51.tinypic.com/ra18ac.jpg[/img]

[willnatalie]

What is the flow of H2 and Air?

[SuperChemie]

30 HYDROGEN 400 AIR

[willnatalie]

take H2 up to 40 and see if the problem still persists. Sometimes the flow of your method can knock out the flame.

[SuperChemie]

I will try that, but it has been at 30 forever without this problem showing up.

[chromatographer1]

When does the flame go out in a run, after 30 sec? 60? 120? several minutes? after a peak elutes from the GC?

30 cc/min is a bit lean but you will get more sensitivity with a leaner flame.

What is your carrier flow? Have you changed gases?

Is Your makeup gas the same, and at the same flow are before?

Rod

[SuperChemie]

The flame goes out at around 30 seconds. Before my solvent peak elutes. My carrier flow is 25ml/min Helium. I have changed the gases a few days before this problem started happening every run. I haven't changed any of my gas flows or settings. Everything is the same as it has been for the past 2 years.

I did a couple of runs over the weekend where I increased the FID temperature to 355 from 300 and the flame did not go out during those runs. I am going to set the FID temp back down to 300 and run samples again today to see if the problem comes back.

[thohry]

The flame goes out at around 30 seconds. Before my solvent peak elutes. My carrier flow is 25ml/min Helium. I have changed the gases a few days before this problem started happening every run. I haven't changed any of my gas flows or settings. Everything is the same as it has been for the past 2 years.

I did a couple of runs over the weekend where I increased the FID temperature to 355 from 300 and the flame did not go out during those runs. I am going to set the FID temp back down to 300 and run samples again today to see if the problem comes back.

You may have to clean the FID' jet and general maintenance for the detector.

[chromatographer1]

SuperChemie

thohry beat me to the answer but I agree with him. I suspect a change in flow due to a partial blockage of deposits in the flame tip, at the end or inside it.

Can't hurt to do a quick probing with a wire to ream it out.

Rod

[SuperChemie]

I did sonicate the Jet in Methanol but I do not (because I can't find it) have a reamer. I do have a new Jet I was going to replace it with.

Any reason why it would work fine with the FID Temp at 355 rather than 300? When I increased the temperature, the problem went away. Then when I brought it back down to 300, the problem came back.

[thohry]

I did sonicate the Jet in Methanol but I do not (because I can't find it) have a reamer. I do have a new Jet I was going to replace it with.

Any reason why it would work fine with the FID Temp at 355 rather than 300? When I increased the temperature, the problem went away. Then when I brought it back down to 300, the problem came back.

Temperature can do something to the size of the hollow.
Sonicating almost do nothing to the deposit inside the tip. You should have a wire, specific one, to clean it.

[Jumpshooter]

An FID jet ought to function properly at 300C. I've heard of people saying that any temp less than 300 is considered "cold"; however, that is only anecdotal. So, the device ought to still be able to stay lit and combust simple hydrocarbons. From readin thru the thread and given that your H2 (40) and Air (400) are satisfactory, it seems that there is some electronic switch that is misfiring at 300C

[AICMM]

SuperChemie,

Buy a set of needle cleaning wires from SGE (also carried by Fischer) and use these to ream the jet tip and the tubing feeding the jet tip. Very inexpensive tool to keep around and can certainly save you in a pinch.

Best regards.

[Peter Apps]

Are you by any chance using chlorinated solvents ?

Peter

[Bigbear]

The cardnal rule for trouble shooting is what was the last thing changed.
Look at the gases you changed. Also check the flow restrictors at the gas boxes ( if 5890).