Chromatography Forum

Hi,
Let me know what are the best columns to use to get a separation from CO to H2-O2-N2-CH4 in Helium balance.
I work in low ppb and I have some problems to get the CO peak in low ppb level

thank you

I'd use a MS5A PLOT column, but there are others here with much more recent experience than I with gas analysis. For CO, you have to ensure the column is well conditioned and the oven ramp removes any strongly bound contaminants, eg water and CO2, in the sample.

Bruce Hamilton

Tiger1076,

Note the other answer I gave you concerning your loss of oxygen peak.

Care must be taken not to OVERCONDITION the MS5A PLOT capillary column or the CO peak will flatten and tail excessively. The detection limit will increase if this occurs. Column replacement will be necessary if this occurs. Glue used to bind the MS5A particles can cause difficulties.

The column should be conditioned with air or oxygen before conditioning with helium or nitrogen.

Excessive temperatures should not be used.

best wishes,

Rod

Hi
i'm using Porapack Q or QS for this separation with FID & Methanizer down to 5 ppb, very stable and reproducible repetitions. MS 5A column responses bad to CO2.

The MS5A packing is acting as it should. MS5A absorbs the linear CO2 just as it absorbs ethane propane and other linear non-branched molecules.

If molecular sieve is used for CO2 analysis the 13X variety is the proper choice, not the 5A.

As long as the air present in your sample does not interfere with the CO methanizing reaction there is no reason NOT to use porous polymer columns like Porapak Q.

For those interested one has to use hydrogen carrier or makeup gas to use a methanizer column.

best wishes,

Rod