Chromatography Forum

Hi,

we're trying to connect a retention gap (~1m, desactivated, unpacked) to our PAH Select column (Agilent). Therefore I used a press fit made of glass. I put the two columns in MeOH, so that the polyimid-layer of the columns swell (heard that on a GC/MS Seminar) and then pushed them into the press fit. I plunged the whole thing into MeOH and rised the pressure to 3 bar, to look for bubbles and see if it sealed well. I tried it several times, but it didn't work. One time there were no bubbles, so i injected a PAH Standard, but the Retention times shifted and the resolution was bad. Next day i looked into the GC oven and the columns fell out of the press fit nearly by their own weight...

Does anybody have experience with press fits or has a good alternative for connecting columns?

By the way, does anybody have experience with the PAH Select column? The seperation of the PAH is pretty good, but after 15 injections of a PAH-Standard it started to tail badly...

The single most important thing in getting a good seal with press fits is a clean square cut at the end of each column. Inspect with a magnifier before you assemble, and practise on old bits of column until you get it right.

Peter

Another trick I have used in the past is to coat the column with extra polyimide resin. The best way to do it is to score the column but don't break it, put a spot of resin on a Kimwipe and gently slide the wipe with resin toward the end of the column. Usually the column will break cleanly as you pass the score and you now have a fresh thin coat of resin right at the sealing point. Push the column into the press tight connector and use a magnifier to verify that you have a nice ring around the entire diameter of the column where it fits to the connector.

When using the extra resin or not, it is also a good idea to heat the column slowly up to the maximum temperature and hold it there for about 30 minutes before ever making injections, this helps to cure the seal and fuse the resin to the connector, even if it is just the resin on the column itself. Also don't be afraid to put a reasonable amount of pressure on the connector when pressing the column in, it takes quite a bit of force to actually crush the column end, but too little and it will not seal.

We use ultimate unions and never have problems with leaking connections.

works just fine.
http://www.agilent.com/cs/library/Suppo ... F03032.pdf