FID air leak

[tkoester]

Hello,

I'm new to the forum and relatively inexperienced with gas chromatography systems. We were having issues lighting the FID on one of our 5890s. While troubleshooting we disconnected the air line coming to the detector weldment from the flow manifold to measure flow. That flow was about 440mL/min. With the line reconnected to the weldment we measured about 400mL/min at the top of the collector body using the o-ringed flow meter adapter. Is this common or should we have the same flow at both points?

Thanks in advance,
Tom

[Bigbear]

Seems about right. For that air flow you will need about 40 cc/min hydrogen.
Make sure the FID is hot before you light it. Do you have a manual gas box or an EPC?
If manual check that the air divert system is working. This works to enrich en the mix to enable ignition.

[tkoester]

Bigbear,

Thanks for the reply. I don't think i made clear in my post that we were able to get the correct mix and light the FID. Just wanted to make sure losing as much as 40ml/min of air was common. Maybe it is leaking out around the bottom assembly?

-Tom

[Bigbear]

There is more restriction due to tubing from the manifold, so this may be contributing to the difference. Is the tubing inserted fully through the O-ring?
You can check for leaks using a 50/50 solution of IPA and water.