Chromatography Forum

I know you don't want to hear this, but you have leak in the line feeding the new instrument.

In your place I would invest in a coil of new copper pipe, some new Swageloks and some PTFE tape and re-do the connection at the helium outlet - using only one reducing bushing not two and making sure that the reducer does not bottom out in the fitting without properly compressing the tape (I am assuming that the outlet has a tapered thread, although from the picture it might be one with an O-ring seal). Then take one, unbroken length of pipe to the connection in the GC, and re-do that with a new nut and new ferrules. Follow the Swagelok instructions to the letter.

Peter

I can't believe it's the gas line when two instruments are hooked up to the same line, and one has a leak and the other doesn't. That doesn't make any sense.

Hello

Don't get me wrong but have you tried really simple diagnostic:

1.Take new Helium cylinder
2.Take some new copper tubing and fittings
3.Make simple system: Helium supply - tubing - Big Universal Trap (new of course) - tubing - GC/MSD

Try to minimize flowpath - do not use valves, T-connectors, strange knobs and regulators.

set up GC flow to 5 ml/min (to remove air quicly from analyzer) and bake out MSD for 3-4 hours (overnight is the best).
Run tune...

If it is ok - it is obvious...your gas line is to be replaced
If it still has leak - it is GC and if system is new ask vendor to take it and test it in factory

I know that you can't believe that other GC is working with the same line but comparing 2 (or even more) GC systems would not help you to diagnose problem.


Regards

Tomasz Kubowicz

I can't believe it's the gas line when two instruments are hooked up to the same line, and one has a leak and the other doesn't. That doesn't make any sense.

You have two connections to the new instrument that the old one does not share; the T that you are using as a straight union with the side branch blanked off - three possible leak sites - and the connection of the line to the EPC, another possible leak.

Peter

That's true. This week I will try hooking up the older system directly to the gas outlet on the bench with the new system, and vice versa. I can already predict how that's going to go.

I am having a very similar problem with my 7890B-5977A GCMS. We are a small lab and don't have the ability to get Agilent to do as much as you have.

I have consistent nitrogen and water around 10% in my air water checks. I understand N2 to be from air but the high water makes absolutely no sense and makes me think it isnt actually an air leak. These values has recently risen to about 18% each with O2 around 3%.

I 3 GCs all set up to the same He tank and no one instruments show these problems.

Any update on fixing your problem? Did you ever replace the transfer line?

While Peter's and others advice is sound, as usual, I agree completely with doing what Tomasz suggests. Get a tank, some new tubing, and connect directly to the GC/MS. I'm surprised Agilent didn't require this as a trouble-shooting solution.

As for Agilent "replacing the whole GC" - they essentially did the same thing for us trouble-shooting an LTM issue. Really impressive they went to that extreme, even though we never got the problem resolved.