Separation argon with nitrogen mixtures, problem with reproducibility.

Chromatography Forum: GC Archives: Separation argon with nitrogen mixtures, problem with reproducibility.
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Kuba on Wednesday, July 25, 2001 - 03:18 am:

Hi !!!
I work in gaseous company. I am new in this area so maybe my question is stupid.
Now we are preparing new mixtures for our big customer 1% of nitrogen in argon. I have problem with obtaining reproducibility in areas making analysis of those mixtures; even I make analysis of reference mixtures (1% of nitrogen in argon). For separation I use MS 5A column 2 meter long, carrier argon N57, flow 85ml/min, detector TCD, columns are regenerated. I s there anybody who could help me.
If some one prepares gaseous mixtures I will willingly exchange experiences.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Wednesday, July 25, 2001 - 08:26 am:

What's the diameter of the column - I think 85 ml/min is awfully high. Another question I have: does it make sense to use argon as carrier if your sample is N2 in argon? I would suggest carrier such as helium so you could quantitate both nitrogen and argon, on relative basis.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Kuba on Thursday, July 26, 2001 - 01:50 am:

Diameter is 1/8. I forgot to mention that there are two columns on the bacflush valve one POROPAK Q and one MS 5A. My chromatograph is designed to determine mixtures with CO2.
So this flow is for two columns each 2 meter long. I tried to analyse using helium, as a carrier is the same.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Thursday, August 2, 2001 - 08:04 am:

At ambient temperature and above Oxygen and Argon are likely to coelute on an MS5A. Maybe you have a leak which allows air into the system.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Thursday, August 2, 2001 - 08:09 am:

That seems like a very fast flow rate. Maybe slowing it down might help. As far as an air leak, if it occured upstream of the injection valve, that might allow unwanted Nitrogen onto the column.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Mike D on Thursday, August 2, 2001 - 09:58 am:

Are you in fact using a purgeable injection valve? You don't say how you are introducing the sample and the air leak idea is plausible if you are using for example a manual gas syringe. I can never get less than 1-2% air entrained with one of these. A well purged rotating injection valve is necessary.


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