CO analysis

[punt]

Hi,

I have a GC setup for trace analysis of CO and CO2.
The carrier gas use is hydrogen, and the sample pass thru Haysep Q and R column to methanizer and FID for detection.

The calibration gas that i use is CO and CO2 in helium as balance gas.
But when i change my calibration gas to CO and CO2 in nitrogen gas, the CO peak seem to be overlap by some other signal.

Does nitrogen gas in the sample matrix interfere with the analysis of CO?

Thank you

[chromatographer1]

You may have a small amount of methane in your gas.

Does this 'peak' appear just after the CO peak?

If so, it is methane.

Rod

[punt]

Hi Rod,

The Peak is not methane. I have injected methane into the GC before and it comes in between CO and CO2. The interference on the CO peak actually is more like the baseline moving up before the CO peak. The shape of the CO peak and area is becomes much larger when the balance gas is nitrogen.

So I am thinking of nitrogen interfere with analysis of CO.

Thank you

[chromatographer1]

When the sample balance is nitrogen your CO peak is LARGER?

I can see the CO peak being smaller due to dilution of the CO peak, somewhat incompletely separating from the N2 through the porous polymers and being slightly smaller, but not larger (in area).

I can also see O2 in the N2 (small amounts) occupying sites where CO might react in your elution through the columns and valving.

But I don't see why CO should be larger using nitrogen as a balance, unless of course, the amount of CO is larger in the standard mix to begin with.

But good luck in your endeavors.

Rod

[punt]

hi Rod,

Thank you for your input.

The CO peak look larger but i do not mean the area is really bigger. But what i mean is the baseline or signal move significant upwards right before the elution of the CO peak thus making the CO peak look bigger and difficult to integrate.

With helium as a balance gas, i dun have this problem.

[chromatographer1]

I suspect the cause is the incomplete separation of the CO from the N2/O2 peak. This means your CO peak is wider than it would be if N2 is missing from the matrix. N2 and CO interfere with each other, competing for the pores in which they can enter within the porous polymer beads.

It usually is not a problem when the CO peak is relatively large or the N2 is a small part of the matrix balance. (like ethylene or propylene)

Usually a Mole sieve or silica column in a trap is used to fully separate the CO from interferences which can affect quanitation.

It takes a very long R column to separate CO from N2.

Good luck,

Rod

[thohry]

Hi,

I have a GC setup for trace analysis of CO and CO2.
The carrier gas use is hydrogen, and the sample pass thru Haysep Q and R column to methanizer and FID for detection.

The calibration gas that i use is CO and CO2 in helium as balance gas.
But when i change my calibration gas to CO and CO2 in nitrogen gas, the CO peak seem to be overlap by some other signal.

Does nitrogen gas in the sample matrix interfere with the analysis of CO?

Thank you

I think N2 may not be as pure as He and the impurities may interfere.
Anyway, could you please show the chromatograms