FID help

[ChEJosh]

Hello. I'm a new grad student in chemical engineering starting to work on my thesis. I'm trying to get my gc up and running, but I'm encountering some problems. My TCD is working fine, but I can't get the flame on my FID to light. I have a air flowrate of about 300-350 ml/min, and I've been varying my hydrogen flowrate from about 5-20%, and nothing is working.

If anyone could give me some helpful insight, I would be most grateful. Thank you.

It's an HP5890, by the way.

[skunked_once]

Your air flows are correct. A 10:1 ratio of air flow to hydrogen flow should work so try hydrogen flows between 30-40 mL/min. Be sure that the flow to the detector auxiliary gas flow is off when trying to light the flame. Here is the procedure that I use on my 5890. Open air and hydrogen tank valves and open the air and hydrogen shutoff valves on the GC. Wait at least 10 minutes for all of the lines to purge out. Now turn off the hydrogen shutoff valve on the GC then press and hold the ignitor button (you should see a glow inside the top of the detector). While the ignitor button is depressed, open the hydrogen shutoff valve on the GC. You should hear a "pop" when the flame lights. When the flame is off, the number value on the "Signal 1" key should be very low. The signal 1 value jumps up then holds steady when the flame is lit. You can also check for condensation by holding a cool beaker just above the detector outlet. Good luck!

[Bricevan]

There are a couple tricks you can try if you just can't seem to find the right settings to get the FID to light by itself.

First, try blowing gently on the glow plug while you're holding down the ignite button. This makes the plug glow a bit brighter and hotter and is sometimes just what is needed.

Second, I've seen glow plugs that seem to be recessed into the wall of the FID a bit too far. You can take a pair of tweezers and gently stretch the glow plug out just a LITTLE farther into the stream of gas (pull too rough, or too far and you'll break it). I've had some success with this before.

[Consumer Products Guy]

First, try blowing gently on the glow plug while you're holding down the ignite button. This makes the plug glow a bit brighter and hotter and is sometimes just what is needed.

Wow, my co-workers have laughed at me for years when I did this, thought I was the only one. {golden Lips CPG}

Also, if there is no glow when pushing the ignitor button, take a 5/16 open-end wrench and loosen, then tighten the ignitor itself, and loosen/tighten the FID mount screws, to improve electrical contact.

[Peter Apps]

Getting an FID to light islike starting a car engine - you need a richer mixture. Turn the air flow down to between 1/2 and 2/3 of its usual flow, then press the igniter. When the flame pops, turn the air up again, and then turn on the make up gas.

5890s had two sizes of flame tip, the narrower one would block completely if a capillary column was pushed in too far. Probably worth checking.

Peter

[gcguy]

The trick with the blowing onto the detector to get it to light is one of my favourite ways to tease newbies.

When their detector won't light and they ask for help, just lean over and blow onto the detector without them seeing you do so. Then tell them that there is nothing wrong with the detector. Switch if off and them get them to try to light it again and they fail. Repeat the blowing step and Hey Presto it lights again when you light it.

This can be repeated several times, but remember to ask questions like "Did you push the button?" "Have you checked the shuttle bipass on/off valve is in the correct position?"
This can go on for ages before I show them what to do.



GCguy

[Spuzzin]

The other thing I would check is the contacts inside the detector body. There is a spring that should sit snugly within the groove on the collector. It may need to be pulled further into the FID body to get a better contact.

I've had occasions where the FID has been lit but the contact was poor so there was no signal being generated.
I suggest checking the FID manually by listening for the 'pop' and checking for moisture on a mirror or spanner.

As for blowing on the detector to get it lit....I thought I was the only one!!

Rich

[ChEJosh]

Just got back into the lab after the weekend, and the blowing thing actually worked! Thanks a lot.

I was surprised at how the pop sound was actually a pop, though. hehe

[Peter Apps]

If you really want to get fancy you can also wave your hand above the detector, sometimes you can even do it by snapping your fingers !

Peter

[Russ]

I wonder if you can convince supervisors that you need to be able to drink alcoholic beverages in the lab to "help" ignite the FID by blowing on it.

[gpronger]

Are we making the coil hotter (I would think cooler) or are we making the it richer (less oxygen in what we're exhaling)?

[aldehyde]

A good way to identify whether you have a flow problem vs. an ignitor problem is to light the stream with a match or cigarette lighter and then check for condensation with a mirror. Or use a flow meter. Also, the blowing trick works and is a magic skill. Its one of the first tricks I picked up and it definitely works--you can see the coil glow brighter. I think its a combination of you blowing gently against the flow (so it sticks around the plug longer) and the plug glowing most intensely (which I would guess means hotter?)

If you aren't seeing a glow from your ignitor you can actually use an ohm meter and check for continuity from the tip to the cable. Its basically the same thing thats in your car cigarette lighter so sometimes they do break.

The other common electronics issue is the electrometer spring not going into position against the collector correctly. You take the top part of the FID off and then reassemble it piece by piece in this case, which usually corrects it. Any grounding issue will generally have your display showing a signal of like 282819238492.