FID flame cannot ignite

Hi pusakcute85,

Good information and responses in this post, I will mark as assumed answered for now . Feel free to update us on your progress.

Regards

James

hi Petur,

Already did as per advice and the FID flame can ignite as perusual. I already change the EPC board for septum purge to the new one due to when the sample has been injected and run in progress, the back detector FID flame will suddenly off and on constantly. Kindly advice on this because it only happened on the 2nd sequence of the run.

Hello again

You are completely sure that the column cut is good, the column connection is correct (not too far up into the FID detector) and there is no blockage using a new jet?

All the set points for flow rates and split rate are correct?

Then I´m starting to think that this is more related to the gas regulation and the ElectricPneumaticControl board.  Maybe the flow rates are not what the instrument reading is indicating and the flame is snuffed out.  Check again that flow rates are right and gas regulation is working properly. Maybe it is time to call in a certified Agilent technician.

Good luck, regards, Pétur

hi Petur,

Already reduce the Makeup(He) from 25.0 to 20.0. And the jet has been changed to the new one. I've manage to make sure the column cut is good and try rerun the squence. i notice the column connection is not quite tighten. Is over tighten can also be one of the reason the FID flame goes out during a run and reattempts to reignite couple of times? What is the best lit offset can be used? before this i use 2.0 pA for the lit offset.

This GC 7890A only used FID back detector for required analysis. And only FID back detector flame that affected by this problem.

Thanks.

Hi

Column connection

The column connection must be tight - column nut is turned until it is "finger tight" + ~1/4 turn extra with a wrench. The graphite ferrule has to make a good grip around the column so it stays in place at the length/position desired (for example detector side 48 mm from the edge of column nut)

If the column is too loose, it can slide down due to the temperature change when running samples (heating and cooling). That is why it is important to review the connections after a few trial runs or the next day. If you mark the column with a marker just below the bolt, then it is usually very obvious if the capillary has slid.

Lit offset

The lit offset is the expected difference between the FID output with the flame lit and the flame output with the flame off.

If the output falls below this value, the FID will attempt to reignite. If the output does not increase by at least this value, the detector shuts down all functions except temperature and makeup gas flow.

The 2,0 picoamps value is a good working value for clean gases and systems. You may want to change this value if having shutdowns like in your case and see if it solves the problem.  If set to "0" the automatic reignite function is disabled. It is possible to set this value between 0 to 99.9 pA.  I suggest testing this with 1,0 pA (signal output is low) or 3,0 or higher (signal output is high).

Suggested flow rates for FID

Carrier gas (hydrogen, helium, nitrogen) 1 to 5 ml/min for capillary columns

Detector gas hydrogen flow range 24 to 60 ml/min*  (suggested 40 ml/min)

Air 200 to 600 mL/min* flow range (suggested 450 ml/min)

*(the hydrogen-to-air ratio should be between 8-12% to keep the flame lit)

Column plus capillary makeup flow range 10 to 60 ml/min (suggested 50 ml/min)

recommended makeup gas = nitrogen

Alternate: helium

In brief:

1. Experiment with the lit offset value.

2. Maybe it is better to increase the makeup flow to 40 ml/min?

3. Change makeup gas to nitrogen (if possible)

4. Check gas purity