Chromatography Forum

Hi
I use Ar/CH4 5% as carrier gas to analyze N2O and SF6 in air, two Unibeads 1S packed columns, backflush mode, with microECD Agilent. I realized after many runs that a contamination of the carrier gas disturb SF6 peak; I solved the problem installing an hydrocarbon trap (from Agilent) downward the pressure regulator, but the contamination seems to be so large to overload the trap capacity just after half use of the cylinder. Since I can not get ride of the batch of the 10 cylinders until next summer (the gc is installed in a top of mountain!), somebody has any idea of which kind of purifier I can use instead of (expensive) hydrocarbon traps? I'm thinking on some catalytic combuster like the Vici one for He, but I'm not sure if it's safety to use with CH4 containing mixture!
thanks

Just a guess; the contaminant could be water which could be removed with dessicant cartridges. You mention the VICI helium purifier, do you have any experience with it ? How well does it work ?

Peter

It looks to me like the Valco purifier will work. There should be no problem using it with methane. However, you may want to try to speak to an engineer first and verify that it can handle 5% methane since the specification is only 10ppm incoming hydrocarbons. If for some reason it can't do it, you can contact me at the link in my signature and I can put together a catalytic air purifier that can handle it.

-Brice

What's the GC detector?

thank's fo the advises
At the moment I've tryed two different purifing traps from Agilent: the Hydrocarbon trap and the multibed trap mainly used to condition He carrier gas for GCMS; and only the Hydrocarbon trap show improvements on reducing contamination; a suspect could be the water content (I've to install soon as possible a silica gel trap to chack this option) or at least something released or by the cylinder itself or by the pressure regulator, but unfortunately I don't have a spare one that fit the Ar cylinder valve.
The Vici filter is basically a catalytic combuster: that's why I'm asking if it's safety or not using it with a large concentration of CH4!

does anybody know something more about this purifier?

http://www.sigmaaldrich.com/catalog/sea ... ELCO/23801

a colleague suggested me to try this one, that should be more or less similar to the Vici one.... (but Vici kindly reccomend to use it with He or N2 and are not interchangeable)

Ar/Me as carrier gas I have never heard of it being used as carrier gas. Your Micro ECD should have a "make up" gas of Ar/Me or Nitrogen to slow the emitted electrons from the source to enhance the Electron Capture of compounds that can. I have to say that for your application I would be using Nitrogen carrier. What flows are you using, I thought that the MicroECD was designed for low flows ? Does Methane trap in the Hydrocarbon trap ? Is the change in retention time of the SF6 related to its ability to displace Methane from the columns pores ?
Puzzled

Ar/Me as carrier gas I have never heard of it being used as carrier gas. Your Micro ECD should have a "make up" gas of Ar/Me or Nitrogen to slow the emitted electrons from the source to enhance the Electron Capture of compounds that can.

I didn't see micro-ECD in the initial post, but the above was the point I wanted to make. Why not use UHP helium as carrier gas and P5 as makeup gas.