Chromatography Forum

Hi Everyone,

I want to estimate how bad of an idea it is to have an extra length of tubing and a bridge in between the column and the detector. Let's say for example you have a 150x4.6mm, 3um column. How much difference would there be between 12" of tubing to the detector vs. 12" of tubing plus a bridge and another 6" of tubing?

Any ideas? Authoritative literature that I can point to would also be helpful . . .

Thanks,

Is a "bridge " a union? A zero-dead volume union?

I meant a union. Like this.

It can't really be zero dead volume. How good is it? If you're just doing conventional HPLC, do you notice it's effect if you put one between the column and the detector? Is there a way to estimate how much it will degrade the separation?

Most of what I've read says that extracolumn effects can be neglected, but it still seems kind of wrong to me.

I find this John Dolan article helpful: viewtopic.php?p=49170#49170
More practical: http://www.mac-mod.com/tr/plumbing-tr.html
The extracolumn effect when using a 4.6x150mm, 5 um column is most likely negligible. However, I would always try to avoid it, particularly behind the column. By the way, Dionex offers new Viper fitting technology that by design guarantees zero dead volume. When using this technology, a union is less troublesome.

It would among other things depend on the tubing diameter...
The simplest thing is to just disconnect the column and measure it...

If you obtain the Upchurch catalogue, you will find a lot of useful information, often including the swept volume of fittings..

Their WWW site ( now called IDEX Health and Science ) also has conversion tables for different tubing lengths and IDs.

http://www.upchurch.com/TechInfo/conversions.asp

They also have some excellent little booklets available about HPLC fittings.

Bruce Hamilton