Joining GC columns together

[wrighty]

Hi all,

just a quick question regarding how to join two GC columns together. I am looking for a specific dimensions in a column which i have found but the columns are too short. is it feasible to join two shorter columns together to achieve my desired length? in addition, what would be the maximum number of columns that could be joined together before the system resolution begins to falter?

Thanks for all opinions

Steve

[Peter Apps]

HI Steve,

It should not be a problem, use Presstight connectors or similar. I vaguely remember a publication on an absurdly long (450m ?) column that was made by joining ordinary columns. If I recall correctly the resolution was slightly better than predicted.

Peter

[larkl]

It's common to join columns, have done it many times. Also, comes in handly if a column breaks and the break isn't near the end. As Peter indicates, the pressfits work well. A few heat cycles and they're fused. Other connections are available, see the normal vendors.

[Spuzzin]

With regard to pressfit connectors. My personal experience is that they aren't very reliable to use. By that I mean I couldn't get a leak free connection on both sides everytime, usually becuase they moved before the columns could fuse.

However, there is a more expensive version that is much more reliable. It uses a standard press fit connector but also has a bracket to hold the columns in place while the columns fuse to the connector. 100% success rate so far with these.

Regards

Rich

[silicaphysics]

Press-fit type (quartz) connectors have evolved over the 25-years or so since they were introduced. Originally, they were flame-formed and sealed better on small OD columns than large ones, due to the curvature of the center restriction offering low angles of contact only to small columns. Even after the restriction was made linear, using a patented laser forming process, leaks still occurred but mostly were due to imperfectly cut column ends.

Sparing the entire history, the newest version of these is able to seal even on ragged column ends, without thermal cycling. They're called Pres2fit and are on Amazon and EBay. There's a video on YouTube where a gas cylinder wrench hangs from a room temperature seal, 0.53mm column to Pres2fit union, and is spun about.

[BMU_VMW]

We use an agilent "ultimate-union" http://www.chem.agilent.com/Library/Sup ... F03032.pdf
and that works great.

In addition to Steve's question.
Is it possible to connect to columns with different fase? e.g. Rxi5_sil MS with Rxi_PAH in order to get higher resolution?
The Rxi5 is better in resolving the "lighter PAH's", the Rxi_PAH does better with the heavier ones.

[Bigbear]

In the past I used one like Agilents made by Supelco. Worked very well.

[Peter Apps]

We use an agilent "ultimate-union" http://www.chem.agilent.com/Library/Sup ... F03032.pdf
and that works great.

In addition to Steve's question.
Is it possible to connect to columns with different fase? e.g. Rxi5_sil MS with Rxi_PAH in order to get higher resolution?
The Rxi5 is better in resolving the "lighter PAH's", the Rxi_PAH does better with the heavier ones.

You can fine tune a separation by joining different columns, you can even fine tune the fine tuning by changing temperature programmes so that the peaks spend different times on the different columns. It is very much an empirical excercise; trying different set-ups to see what works.

Peter

[James_Ball]

With regard to pressfit connectors. My personal experience is that they aren't very reliable to use. By that I mean I couldn't get a leak free connection on both sides everytime, usually becuase they moved before the columns could fuse.

However, there is a more expensive version that is much more reliable. It uses a standard press fit connector but also has a bracket to hold the columns in place while the columns fuse to the connector. 100% success rate so far with these.

Regards

Rich

I discovered a trick a long long time ago, I think it came from a Restek technote, that works well even on the old style presstight connectors. You need a small bottle of the polyimide resin. You place a Kemwipe over the top of the bottle of resin and invert to give a nice little circle of the resin on the Kemwipe. Then you score your column where you want to cut it but do not break it off. Take the Kemwipe and wrap it around the column upstream of the score and pinch it tightly and slide it towards the end of the column, as you pass the score the column will break usually with a clean cut. You now have a nice thin coat of fresh resin right at the cut, when you push on the presstight connector you will see a nice ring of resin sealing the connection if you look through a magnifying glass. Pre-bake the column starting at 50c for about 10 minutes, then go to 150c for another 10 minutes then to max temp for a little while and the seal will be good and solid.

This has always worked well for me. Just don't expect to be able to reuse the connector because that ring of resin will not come out later.

[MSCHemist]

I found an old union in my lab with nuts for standard graphite/vespel ferrules. I use to to join a retention gap to the column. I've had it leak on me once do the vespel ferrule expansion/contraction but otherwise it works.