Chromatography Forum

With our GC/MS (GC6890, MSD5973) we often face problems with air leak. At low oven temperatures the baseline level for mass 32 of oxygene is very high (100000 and higher). It reduces at higher temperatures (about 150°C). Good level for mass 32 is about 10000.
After maintaining the MSD it's ok, but after a few weeks it comes again. Mostly it can be improved by fastening the column nut of the MSD interface inside the oven. Changing the inlet septa gave no change.

So I assume the problem comes from an air leak at the interface. I know, that the nut has to be retightened several times after installing a new ferrule, but how could I improve the connection more permanently? We use Agilent ferrules made of 85/15% Vespel/Graphit (0.5mm ID, long, 5062-3506), which are recommended for GC/MS according Agilent catalogue. Has anybody a better recommandation?

Emsman,

I had a similar problem on a GC-MS sometime ago when using T higher than 350 C and due to the thermal cycling of the oven I had to retight the nut at the interface every 2-3 runs.

Now I'm using Siltite ferrules http://www.sge.com/products/gc--lc-supp ... -ferrules3

They work fine. The only drawback is they are really permanent. Once applied you have to cut the column to change them.

Regards,
bhuvfe

Thank You, bhuvfe, for this information.
I will try these ferrules. I already now cut a small piece of the column, when changing it.

Emsman

I also recommend SilTite, and makes sure the inlet connections are leak-free, ike around the liner, and the inlet ones in the oven compartment. How often are you changing septa?

We are changing septa maybe once a month. The instrument is not running 24/7, but nearly everyday during working times.

I'll try this SilTite ferrules....

Thanks for help
Emsman