Chromatography Forum

can you please suggest me a suitable GC method to analyse Ar(30 PPM),O2(40 PPM) and N2 (Balance).

Regards,

Naresh

If you use mole sieve available commercially (with the exception of Supelco's specially prepared MS 5A, if they still sell it, that is) you must use subambient oven temperatures to achieve separation of O2 and Ar.

Some thick film MS5A capillary may be capable of the separation, but when the NIST asked me to prepare them a packed column that would work at ambient temperatures I sent them a 9 meter 2.1mm ID column containing a special preparation of MS 5A.

I don't know if Supelco continued to make this packing or not.

I can send you a chromatogram example of air producing three peaks (O2, N2, and Ar) if you send me your email address.

best wishes,

Rod

Agilent claim in tech note 5990-8700 that you can do this on their (Varian) micro-GC using a 5A molesieve column at 40C. The note is a bit short on detail, I was interested to see the plate count they claim. The column will be pretty narrow though (and 20m long), and the separation was about as close as you'd like it.

Dear Rod,

Thank you very much for your reply.

Please send me example chromatogram for this seperation on my email ID: nareshsharma2k@yahoo.com

Also in case if one needs to know only Ar and O2 impurity peaks ( PPM level conc.) in a Ar,O2,N2 mixture analysis,will it be helpful to use N2 as carrier gas.

Regards,

Naresh
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If you use mole sieve available commercially (with the exception of Supelco's specially prepared MS 5A, if they still sell it, that is) you must use subambient oven temperatures to achieve separation of O2 and Ar.

Some thick film MS5A capillary may be capable of the separation, but when the NIST asked me to prepare them a packed column that would work at ambient temperatures I sent them a 9 meter 2.1mm ID column containing a special preparation of MS 5A.

I don't know if Supelco continued to make this packing or not.

I can send you a chromatogram example of air producing three peaks (O2, N2, and Ar) if you send me your email address.

best wishes,

Rod

http://i5.tinypic.com/24ci72v.jpg

This is a chromatogram of a sample of air 100 microliters injected onto a 9m 2.1mm ID packed column of MS5A (special Supelco preparation) which is not a common commercial packing at 28C. A TCD of a HP 6890 was used.

0.9% Argon 21% oxygen and 78% nitrogen

This packing used with a larger injection of nitrogen will easily separate and detect ppm levels of Argon and Oxygen and was used by a government agency to certify gas blends at a range of 0 to 50 ppm levels.

Rod