Chromatography Forum

Hallo everybody,
I'm looking for a column to separate O2 and Ar (carrier He) possibly without subambient temperature.
So far I've used Molsieve 5A Restek capillary column, 30 m and 0.53mm ID, but it is some years old.
Does anyone know if some other column is available (someone told me about Hayesep but I did not get the details) and eventual suggestions?
Thanks
Maurizio

I can't totally resolve Ar and O2 (in air) at 40 °C with my molecular sieve column. I found an old Chrompack application note where they show baseline resolution of argon and oxygen on a 5-angstrom molecular sieve (50 m x 0.53 mm x 50 µm) at 30 °C isothermal and hydrogen as the carrier gas. It looks like a dilute standard of the gases so the oxygen peak is not massive. They used a TCD as the detector.

If you can't go subambient, it could be tough.

Most 5A mole sieve packings will not separate oxygen and argon due to the damage done when manufactured. Supelco has in the past made a column what will separate them at 30°C with helium carrier. (9 meter 2.1mm ID packed SS column) The example chromatogram below was using TCD and 100 microliters of air injected. Air has 0.9% Argon 21% Oxygen and 78% of Nitrogen.

You might call the product manager at Supelco for the packed column line and ask if they will make you a such a column.



This is how well the common packing will separate Ar and O2.



best wishes,

Rod

Restek has chromatograms separating O2 and Ar but using capillary columns in a GC using HID where only a few microliters of air is injected.

Your separation using either column will greatly improve if you can lower the temperature to 25°C or even 22°C. I achieved this by putting bowls of ice in the GC oven. Of course if you can go subambient with liquid nitrogen all the better.

I would ask the vendor you choose to provide test chromatograms of the column you purchase.

Expect to pay $700 to $1200 for the column to perform the separation. That may be cheaper than buying a HID or using liquid nitrogen.

best wishes,

Rod

Great solution for low level applications, but the OP did not say why he wanted the separation and the levels required ? I've been involved in applications looking for these gases in CO2 and for Oxygen in pure Argon. Both are possible

Here is a chromatogram of air, 100 microliters with an Agilent microTCD at 25C. Argon is about 1 microliter and oxygen is about 21 microliters of gas. The improved separation is due to the lower temperature of 25C and an improved manufacturing process of packing separation.

best wishes

Rod

Thanks all for your replies and expecially to Rod. I will try to contact you soon
Maurizio

If there any new columns for Ar and O2 separation? Agilent 7890

Do you mean CAPILLARY columns?

Rod

Maurizio

Did you find a column?

Rod

For measurement on-site, or if you have lots of gas, you can use a fuel cell oxygen analyser like a Teledyne 311. Other than that, we look for ppm-level argon in oxygen using a Thermo Trace GC which is set up with oxygen absorber traps. It's a complex beast inside though.

Oven temperature is everything here. These peaks elute with k=1 at 30C meaning with a30m x 0.53mm Rt MSieve 5A or MXT Msieve 5A you get a baseline separation

packed column also can be used, but here we need efficiency also (well packed) and you will pay in time as Rod's chromatograms clearly show.

why not take a different approach if this is so important:

measure Argon: find a way to remove the O2 by suing a reactive adsorbent in the liner.This should be pretty easy.

measure O2: use Argon as carrier gas. yes , not ve3ry sensitive, but who cares if we have to inejct a lot and get a broiadened peak? there is enough room on a5A column, and as long as its reproducible?


jaap de zeeuw, restek corporation

You can contact LDetek. They have a column called ArgoTek that can separate ppm/ppb/% Argon from pure Oxygen at 45 Celcius and 30sccm Helium carrier flow. It is exactly what you are looking for.
It is a 8' long packed type column.

You can contact us at dgagne@ldetek.com or info@ldetek.com

Have a look at the web site : www.ldetek.com

We can send you the chromatograms by email.

Kind Regards

Dany