Chromatography Forum

HI? My question is simple. I think i have a leak somewhere in my system (HP 5971MSD/5890GC) if i cap the end of the transfer line i can obtain a proper vacuum (hig N2 and 02, but they dont interfere) and no water; but if i connect my column and low flow, the signal of water appears. I have already checked the muts and connection, and i am almost sure they are gas tight. My question is: Is it possible that the sealing with the top plate of the Mass Spec could be sealed when no flow is going through, but a small leak could appear when i have some flow in it? That could explain my leak.

Thanks

If you are still getting significant amounts of nitrogen and oxygen with the transfer line capped then this indicated to me you have a leak in the MS system. It will be much easier to track a problem with water in the rest of the system if you get the MS operating correctly first. Also, I have seen some columns throw off water for many hours (at trace levels) when they haven't been used for some time. Maybe even the outer polyimide layer desorbing water from the part that is in the heated transfer line. The water should decrease eventually if these are the sources. When I used an older 5972 we generally had to leave it pump at leats 24 hours, 48 was better especially if you are doing trace level work.

Regards,
Mark

I have the same equipment as you, and I agree completely with Mark: if you have high nitrogen and oxygen with the MSD capped off, then you have a leak in the MSD or the transfer line cap. Fix that first, then add the GC part.