Chromatography Forum

I am using an HP5890 with a TCD. The instrument is quite old but overall in good shape. Because of the age of the instrument, an issue I am having is a reoccuring leak in the Aux line which causes a dropping baseline during a run. What is happening is the constant heating and cooling causes the line to leak, because it was happening so frequently, even after completely replacing the line, we modified the detector end to include some stronger fittings thinking that would solve the problem. While it did solve the existing problem, it created another. Because the fittings we added have ferrules, they loosen up with the heating of the instrument which again causes a leak, and a drop in the baseline. I am trying to work with Swagelok to make a custom male end tube adapter which will hopefully solve the problem, but I wanted to see if anyone else has had this type of issue and what their fix was. There may be better ideas out there that I haven't thought of. Thanks for the help!

Don't go crazy with adapters. You can attach to a TCD using an 8th inch swage nut, TCD ferrule and back ferrule. The other option is an 8th inch swage nut, 8th inch ferrule, and a capillary adapter.

This site has pictures showing both options:

http://www.cobertassoc.com/agilent_6890 ... d_supp.htm

The option I prefer (with the TCD ferrule/back ferrule combination) is near the bottom of the page and has a bluish background. The ferrule tends to get stuck in the TCD if you over tighten, but it works very well if you aren't changing columns often. If you change columns a lot go with the capillary adapter so you are more often than not leaving the TCD seal intact.

When I attach a column to a TCD I get it "tight" but try not to over tighten, I then increase the oven T to 5 or 10 degrees above the max temp in my oven program, I let it sit for a few minutes, then I give it just a bit more of a turn with the wrench. This will definitely keep it leak tight and should help you keep from getting the ferrule stuck.

In either case, the site has all the applicable part numbers. Let us know if you have more questions .

I have a capillary column which requires an auxiliary line so the setups you provided won't work for my system. Thank you though.

Be careful with this. When we first got our SRI, we saw the same thing. Ended up the changing temperatures of the oven caused the signal change, but they were not the cause of the leak.