GC issue with seperating Ar from N2

[cheq]

Hello all, I am trying to use the TCD to detect ~0.01% of N2 in a argon sweep gas stream.

GC conditions:
carrier gas: He
TCD temp 200C, filament temp 220C.

I have a molsieve column to seperate N2 and argon. But N2 peak always follows Ar peak which made it not analyzable for sush a low concentration of N2.

Would anyone please suggest a way to solve this issue? Any way I can separate these two peaks more effectively?

[chromatographer1]

You should have no problem if you had a good mole sieve column and were using conditions appropriate for the analysis.



This chromatogram shows Argon 1%, Oxygen 20%, and Nitrogen 78%. It is overkill for the O2 and N2 separation but the column could be shortened and/or the temperature increased.

Your analysis:

OVEN TEMP ?

FLOW RATE ?

COLUMN ID?

FILM THICKNESS ? or PARTICLE MESH SIZE RANGE ?

TYPE OF MS (5A or 13X or other) ?

COLUMN LENGTH ?

SAMPLE LOOP SIZE ?

best wishes,

Rod

[cheq]

I have the following column and running @ 200C TCD. I have trace amount of N2 in Argon, 0.01% in ~99.9% Argon and also ~0.1%CO2 in the gas stream to be analyzed. I can not get the Ar and N2 peak separate out effectively. Rod, Would you have any suggestions? Thanks, George

OVEN TEMP 80C

FLOW RATE 20ml/min He

COLUMN ID 1/8"

FILM THICKNESS ? or PARTICLE MESH SIZE RANGE 60-80 MESH

TYPE OF MS (5A or 13X or other) 5A

COLUMN LENGTH 1M

SAMPLE LOOP SIZE 25ul

You should have no problem if you had a good mole sieve column and were using conditions appropriate for the analysis.



This chromatogram shows Argon 1%, Oxygen 20%, and Nitrogen 78%. It is overkill for the O2 and N2 separation but the column could be shortened and/or the temperature increased.

Your analysis:

OVEN TEMP ?

FLOW RATE ?

COLUMN ID?

FILM THICKNESS ? or PARTICLE MESH SIZE RANGE ?

TYPE OF MS (5A or 13X or other) ?

COLUMN LENGTH ?

SAMPLE LOOP SIZE ?

best wishes,

Rod

[chromatographer1]

I would suggest you spend a $100-150 and buy a 3m column that is conditioned. A 1 meter column is a bit SHORT for separating ~100% peak from 100 ppm.

You could also reduce your temperature of your column to 35°C or 40°C.

That by itself might be enough to solve your problem.

best wishes,

Rod

[cheq]

Thanks, Rod.

By temperature of the column, do you mean the oven temperature? Because I just tried to reduce TCD temperature and it gave me extra unknown peaks.

Also, will the injector temperature matter much? What happen if the injector temperature is kept at 150C? Or should it be lowered to 40C too?

Thank you again.

I would suggest you spend a $100-150 and buy a 3m column that is conditioned. A 1 meter column is a bit SHORT for separating ~100% peak from 100 ppm.

You could also reduce your temperature of your column to 35°C or 40°C.

That by itself might be enough to solve your problem.

best wishes,

Rod

[chromatographer1]

Just lower the OVEN temperature. If you keep everything else the same you will be fine. You COULD lower the flow rate with only 25 microliters of sample. You could do as low as 8cc/min. of Helium. Halving the flow to 10 will DOUBLE your response approximately. Keep your filament hot or you will lose sensitivity.

best wishes,

Rod