Chromatography Forum

Hi all,

This is a new topic about the TCD on my 5890. I have been having issues with analyzing N2 and O2 (I discussed this in a previous thread).

I am now wondering if I have completely damaged the filaments on the TCD since I now get absolutely no peaks for either N2 or O2 where at least before I was getting peaks, although they were inconsistent. I did find that the injector nut kept coming loose (any ideas of why this would be?) and this may have caused the previous problems I was having. I don't think it is a flow ratio issue.

The TCD background signal is now sitting at a steady 23.6 without moving.

I am using the following conditions:

Tank pressure: 40 PSI
column flow: 6.6 mls/min
column + aux flow: 9.4 mls/min
ref flow: 31.4
ref manual says 3 x col+aux flow for the ref flow
split/splitless flow: 35
septum purge flow: 1.8
helium carrier gas
molsieve 5x col....0.53 um


So my question is:

How do I test the filaments...I know that I have to use a multi-meter and test the resistance but really not exactly sure how to do that...do I test the pair of filaments together..i.e. one lead of the multi-meter on one filament, the other lead on the other filament...test it against ground or what?.

A bit in the dark about this procedure so any help is appreciated.

Then if I find that the filaments are damaged, can I replace them easily?

And also, could I have damaged the filaments by continuously injecting 100 ul of room air several times? Or could the fact that the injector nut kept coming lose resulted in lots more O2 getting to the filaments? I know O2 can damage the filaments.

All help is appreciated.

There is only one filament in a 5890 TCD detector. This filament is thinner than a human hair, and you cannot change it in the field. I believe that the detectors are still available on an exchange basis. At room temperature the filament resistance is about 9 ohms. Injecting 100 ul of air several times will not damage the filament.

Gasman

Thanks Gasman for your reply. There are two leads coming off the TCD so can I assume to measure the resistance then that I just put the +/- ohmmeter leads on each of TCD leads?

Yes

Gasman

One other thing. Can you hear the switching valve operating. This is the valve on top of the oven close to the TCD. You should be able to hear it switching at 5Hz when you have the filament turned on and the detector is at temperature.

Gasman

Yes, it is still ticking. Does that mean there is no filament problem and there really is just a gas flow/ratio issue?