Chromatography Forum

Hello.

Recently I had a mixture gas analyzed by an institute

the mixture gas is H2, CH4, CO, CO2 in N2 balance.

CH4, CO, CO2 are almost matched to known gas compositions

but H2 was lower, N2 was higher

I wonder why this happened.

here are the conditions of analysis

Detector: TCD
Carrier: He
Column: SCION-LOT Q w/ 1PT 25 m 0.32 mm 10 um

is it because they used a capillary column?

Thanks.

Do you know what the balance gas of their calibration standard is?

For permanent gas analysis, if there's a discrepancy in the type of balance gas used for calibration vs. actual samples, this can skew the results quite significantly for some gases, not so much for others. If your sample is a nitrogen balance and they're calibrating for natural gas (methane balance), this would skew things enough (but I have found CO2 concentrations don't change terribly much with variation of balance).

I don't think the column type matters terribly much. There is also a possibility that the H2 is reacting with something in the line and dropping out, and because the N2 concentration is likely back-calculated it is thus increasing to compensate. But not sure if this is likely to occur, I don't often analyse samples with high H2.

That said, I have had a problem with high H2 samples where the lines are not sufficiently purged out by the H2 sample (ostensibly due to the low density of H2) and I see carry-over which is difficult to work around, but not sure if that's applicable to your situation.