Chromatography Forum

Hi Guys,

I was wondering if anyone would have some insight into being able to achieve this. I need to find out how much argon is in our bulk nitrogen. I am using a PDHID and I think low level Oxygen is interfering with my quantification of the argon. Any help is greatly appreciated.

SkylineGTR112,

I am highly confident that you have argon in your nitrogen. The way that I understand air sep nitrogen is made (from a buddy in the business) they will make it either oxygen "rich" or argon "rich". Most of the time I believe they move argon rich. And, to compound things further, oxygen and argon don't want to separate.....

So, what column are you using and do you have access to cryo in the facility and on your instrument? Do your standards have separate oxygen and argon so that if you do separate, you can quantify them?

Best regards.

I have a cryogenic system hooked up to the GC and I am running a Molsieve 5a column, but I think I may have found another problem and my cryo system isn't working correctly. The lines aren't cooling and I thing maybe the valve for introducing the CO2 might be bad.

Firstly, liquid CO2 lines don't cool, all of the cooling occurs as the liquid converts to a gas outside the nozzle in the oven.

For that to happen, several things have to happen.
1. The CO2 cylinder must have a liquid eductor tube outlet that your system is connected to.
2. The headspace in the CO2 cylinder must be the highest pressure part of the system to the nozzle to ensure liquid is existing the nozzle, not gaseous CO2. Some liquid CO2 cylinders have extra helium pressure applied during filling, if not, you may have to heat the top of the cylinder - especially if it's in a colder part of building or outside - pouring 10 litres of hot water over the cylinder worked for me...
3. The nozzle must be clean, Liquid CO2 has a nasty habit of holding fine particles - I put a7um high pressure filter upstream of the nozzle.

When the system is working properly, it's pulsing and sounds like steam train leaving the station. If it's a continuous light hiss, with not cooling, then your CO2 is gaseous upstream of the nozzle.

Please keep having fun,

Bruce Hamilton

After I inspected the CO2 bottle, I found that the dip tube is either missing or broken, got that repaired and now I'm just trying to get the separation.

Is the Molesieve 5A a packed or PLOT column?

If it is a PLOT column, make sure it is able to separate argon and oxygen at ambient or even slightly elevated temperatures. If given a choice of film thicknesses, always opt for the thicker film for Ar/O2 separation.

Some manufacturers market a "thin film" to elute CO in a timely fashion (CO takes a long time elute from the thick film columns). The problem with the thinner film is that your resolution for Ar/O2 at cryo temperatures will not be as large as it would be with the "thick film".

Also, absorbed water will reduce retention and could adversely affect the Ar/O2 separation. Follow the manufacturer's recommendations for column conditioning to remove water.

The column is packed, I'm also wondering if the balance gas is causing a matrix effect, my standard is in Helium and the sample is in nitrogen.

Hi Skyline,
I have done this application many times with a GC, using an heartcut configuration. The precolumn was a standard 5A 4' long 60/80 and the second was a Calcium threated synthetic Zeolite column.
I have some chromatograms that shows a perfect Ar-O2 separation in pure N2. I have been able to measure down to 10ppb ar and 10ppb O2 in pure N2. Even Ar in pure O2 since the separation is perfect. The beauty of the thing is that the second column can be operated at 45Celcius.
You can get in contact with me if you need more details by email at : instrumentseoul@gmail.com

thanks