Chromatography Forum

We have a Agilent GC6890, and yesterday we tried to calibrate the capillary column with FID detector on GC. The calibration gas components are C2H2, C2H4 and C2H6. The carrier gas in the GC and balance gas in the calibration gas are Helium. When we calibrated it, a issue happened that the FID flame kept switching on and off in the calibrating process until the first peak of C2H2 generated. We calibrated the GC with the some gas sample four time, while the FID flame was keeping on only at the first time. In the next three calibrations, the FID flame just switched on and off as I mentioned above. Also the times of flame on and off for different calibrations looks increase. When the flame on, there was also a sound like explosion.

Again, the flow rate for H2, Air, makeup gas and column are 30ml/min, 300ml/min, 26ml/min and 4ml/min. The temperature of the FID detector is kept on 300 degree C.

Is anyone met this issue before? What is the reason for this issue? How to solve it? Thanks a lot.

I'd check for leaks. A properly sealed system with the correct flows should stay lit. My 5890-FID can be a real bear to light but it stays on once lit. I shut off the makeup gas while lighting it and sometimes turn up the H2 a bit.

I'd check for leaks. A properly sealed system with the correct flows should stay lit. My 5890-FID can be a real bear to light but it stays on once lit. I shut off the makeup gas while lighting it and sometimes turn up the H2 a bit.

Thanks a lot. Do you mean to check the possible leaks in the connection of column and detector? or some other places?

What is the FID signal in pA (before 1st peak) ?

What is the lit off limit for FID ?

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Has this instrument been up and running for a while and this just started happening? Did you make any changes or do any maintenance before this started happening? Make sure the pressure on your regulators supplying your gases hasn't changed. Also, if you replaced the jet, there's one for capillary columns and one for packed. If you don't have the correct jet installed, you will have flame outs.

What is the FID signal in pA (before 1st peak) ?

What is the lit off limit for FID ?

We had to increase our offset limit on one 6890 as the flame would go out, re-ignite, etc.

a leak in any of the gas supplies or the FID unit itself will make it not stay lit.

Thanks guys. The issue has been solved. The reason is that the flow rate of makeup gas is too high compared to H2 and Air flow rate. We just increased the flow rate of H2 and Air to 40ml/min and 400ml/min while kept the makeup gas flow rate same as before, and then the flame is always on. So I'd like to just show this possibility here and help others who make meet similar issue with GC.

Thanks guys. The issue has been solved. The reason is that the flow rate of makeup gas is too high compared to H2 and Air flow rate. We just increased the flow rate of H2 and Air to 40ml/min and 400ml/min while kept the makeup gas flow rate same as before, and then the flame is always on. So I'd like to just show this possibility here and help others who make meet similar issue with GC.

Flows you quoted in your 1st post seemd quite O.K. I wouldn't suspect them for problems with stable FID flame.

I pretty much agree, though would use a bit more air and hydrogen, but as you say it should have been close enough.