no inlet pressure after installing headspace transfer line

[MestizoJoe]

Hi,

A few weeks ago I was re-connecting the headspace transfer line to the GC inlet. Afterwards, there was no inlet pressure. I got busy and someone else put it back together and it worked for them. They couldn't say what they did that was different.

This happened again on Monday. I replaced the liner, gold seal, and o-ring and when I put the transfer line back together I had no pressure.

As a result I took it apart and put it back together twice more and broke the transfer line on the third try...

What are some common mistakes that might have caused no pressure?

[chromatographer1]

What about the o-ring in the septum cap?

Rod

[Meerkat]

sounds like the helium gas tank is low

[Peter Apps]

This all depends what you are connecting where, how the gas supply is plumbed in and controlled i.e. by the GC EPC or by the headpacer.

As you now know from experience, blindly pulling things apart and putting them back together in the hope that the laboratory spirits will smile on you is not the most effective way of troubleshooting.

Have you checked for leaks with a leak seeker ?

Peter

[MestizoJoe]

Yes I also changed the o-ring and septum.

The headspace transfer line was connected to the gc split/splitless inlet. The gas carrier in the headspace is controlled by the GC. Helium tank was fine too.

And I didn't have a leak seeker.

[Steve Reimer]

Broken transfer line... are you overtightening the fittings and crimping off the flow?
Or the line was cracked and the extent of leakage was dependent on position.
Or something isn't turned on.

I have done all the above at least once.

[chromatographer1]

As Steve clearly has posted, it is a leak or a blockage.

Just find it.

Rod

[Peter Apps]

I am pretty sure that you can get a leak seeker for less than the cost of a transfer line.

Peter

[chromatographer1]

Leak checkers (devices, not a bottle of IPA and a pipette) cost a pretty penny here in us USA.

A SS transfer line may cost $4 a foot.

BIG DIFFERENCE, Peter.



Rod

[Peter Apps]

Hi Rod

Leakseekers are not cheap here either, but all the HS transfer lines I've seen (for Agilent, Dani and Varian clones) have heaters etc built in and are even more expensive, more like $400 a foot !.

I honestly can't see how a GC lab can run without a leak seeker.

Peter

[chromatographer1]

The transfer line itself is a FSOT tube siting inside what you are describing.
(sometimes they are nickel alloy)

It is replaceable and costs only a few dollars.

best wishes,

Rod

[Peter Apps]

Hi Rod

Then the design is different to any headspacer I have worked on; they all had "transfer lines" which had a steel/nickel/ silcosteel sample path wrapped with a heater element, temperature sensor and insulation. I never managed to get the sample path tube out of the whole assembly without dismantling (= destroying) the whole thing. To get an inert flow path in the days before silcosteel I used to thread deactivated fused silica inside the nickel sample flow tube and connect the silica to the six-port valve with a vespel ferrule, the press-fit the downstream end of the silica to the column.

So, MestizoJoe, what id broken on your transfer line, and what do you have to replace ?

Peter

[scottythree]

To confirm transfer line HS leak/blockage why not disconnect gas from the HS and route it directly to the inlet?

[Bigbear]

Is it an Agilent GC? When I installed a P&T to my 6890 I cut the 1/16" line going to the inlet ( be careful the line to cut is the one that goes through a "flat" spot on the fitting).
Then using swaged fittings put the headspace in series between the cut you made. Connect the heated tube of the transfer line to the cut @ inlet and connect the other CG line to the headspace supply ( unheated tube).

[chromatographer1]

Hi Peter,

I had a PE HS40 and a Tekmar 7000 which I replaced the interior nickel tubing line while leaving the heating element and insulation intact. So my experience differs from yours.

I used FSOT and then used Silcosteel lines, connecting them to my analytical column with deactivated SS unions.

They usually lasted for more than a year before requiring replacement.

Of course that was almost 20 years ago and designs may have changed since then.

MestizoJoe,

Just step by step determine where you have flow and where it stops. If you have flow but no pressure then you have a leak.

good luck in finding the problem.

Rod