Chromatography Forum

Hi Everyone,

I had my FID repaired this week because it would not ignite. The repair was successful and it ist working again...except for the results. The Baseline is constant at about 40000 counts. I have run now two sequences since the repair. Both hat the high baseline except in the first one after 27 injection the baseline fell to normal again....then I had to change Hydrogen an the baseline came again up but not as I hoped again falling after some injections....it is nailed at 40000 counts. I have checked the system for leaks but everything is ok.
What could it be......??

Some details about the system: HP 5890 Series II with split splitless injector, FID, DB-XLB 30m*0.25*0.5 and an TSG-530660-P (10m*0.53 coated with OV-1701-OH), carrier gas H2, and splitless injection of 1 microliter silanized componets (wine in our case).

Would be grateful for any help

Cheers
Andreas

Do some trouble shooting. Has anyone ever taught you this?

Ask around for someone who is experienced.

If not:

Your traps or gas lines or GC are contaminated.

Disconnect your columns from the FID. Cap off the FID. Does the signal drop to zero?

If it did, then your carrier gas is contaminated.
If they are contaminated then your GC pneumatics are too.

If not, then your air or hydrogen or make-up gas pneumatics are contaminated.

Replace each one until you find the source.

best wishes,

Rod

Disconnecting the column and blocking off the bottom of the FID with a column nut and no hole ferrule is a good place to start. If your detector gases are clean the pA should drop to under 20.

Since the FID was recently serviced, the problem is likely related.. The top of the FID, the castle which contains the collector, may not have been installed properly and there is a short causing the high spike. Although I would have expected it to max out higher than 40,000 pA. Have someone that is familiar with the FID disassemble the top and reassemble it. When it is disassembled take a look at the interconnect/spring, it should not be bent or other way disformed.

Thank you so much for all the help.

I took a look into the manuals and I talked again with my service technician, and he told me that the insulators are not in good condition. Why he did not change them it is a mystery.... I ordered now a collector assembly kit and I will exchange the parts.

I have a lot of experciense with other detectors but very little with FID... So....I'm learning....