GCMS leak? High N2 and low O2

[wan]

Hi Don,

Sorry. I was referring to the inlet nut where we change the septum and liner. I was told it will loosen slightly with time/injections, but not to the extent of losing pressure.

We're using graphite/vespel ferrules for all our GCMS. I supposed those ferrules are far away from each other in your lab now? We're fanatic labellers in our lab, so everything is double labelled and doubled checked before being used.

[Don_Hilton]

I don't believe that I have encountered the fitting on the top of the inlet coming loose, at least on 5890 and 6890 series GCs. (The 5710 had a different inlet - as it was a conversion from packed columns - different story.) New one for me.

And the graphite ferrules were left behind a couple of job changes ago. And you know the drill: when someone leaves everbody checkes to see what treasures were left behind. I hope the ferrules served the next owner well...

[Peter Apps]

I have never heard of an inlet nut working loose, but after 100 injections I would not be surprised that the septum itself was starting to leak. The most crtical factor in septum life is the tip of the needle. If you are using standard autosampler syringes you should be OK, but just check that you have a smooth cone-shaped tip on the needle. Paradoxically, if you tighten the nut too much, as you might do in anticipation of its coming loose, wear on the septum is actually worse and it starts leaking even sooner. You might need to look at a Merlin microseal or a Jade valve for sequenses of 300 injections.

Peter

[wan]

Perhaps the engineer, who told me it might loosen, was confused. I spoke to him over the phone, so I think he must be referring to a different part when he said that.

Strangely, loosening of the inlet nut is what we're encountering. We're using the standard autosampler syringes and we usually tighten that nut finger tight. I really don't want to over tighten as what Peter had mentioned.

It's just a weird situation.

[Peter Apps]

Weird indeed, and I would have thought that Agilent would be more interested.

Does the syringe barrel actually touch the nut when it injects ? - I can just about imagine that a light tap x 100 on a treaded part could make it loosen. You might need to re-initialise the syringe carriage on the autosampler.

What you could also try is to overtighten the nut by about half a turn, then back it off to the correct tightness. Friction between the septum and the nut will then be tending to tighten the nut rather than loosen it.

Peter

[wan]

Ah, thanks for the tips. I'll go check and try 'em. Thanks again!

[Don_Hilton]

Are we talking about the nut that holds the septum in or the nut that holds the top on the inlet (where you change the inlet liner)? If it is that larger nut, be sure you tighten it firmly. The tool Agelent supplies with the instrument is short, but you can apply some pressure and ensure the nut is tight.