Issues with area counts and calibration for Air, N2, O2

Discussions about GC and other "gas phase" separation techniques.

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We recently bought a Agilent 490 Micro-GC with 20m MS5A and a 3mPBQ+20m PPU columns.

The first concern was with the low area counts we are getting (ex. 0.035 for O2, 0.008 for CO2)

We were told by Agilent that the area count is arbitrary and that there is nothing wrong with the area counts.

Our standards contain O2, N2, CF4, CO2 and CO at 5ppm, 10ppm and 100ppm

We are able to get good peaks and good repeatability of area counts.

We are able to calibrate successfully for the CF4, CO2 and CO analytes but not Air (3mPBQ+20m PPU) and the O2 and N2 (MS5A).
There is excellent agreement at all levels of calibration for CF4, CO2 and CO.

When calibration is done with the 10ppm standard and checking against the 5ppm standard the values are higher (~17 for air and ~8-9 for N2 and O2) and it doesn't even come close to 100ppm (200ppm for air) when checking the calibration against the 100ppm standard.

The curve is linear when all three levels of calibration are used but not linear to the origin. We still can't get agreements between standards when using multi-level calibration.

Any insight? We suspect there may be a leak or something similar.
Based on my experience, I think you are being a bit optimistic to think you can accurately measure 5,10 ppm of O2, N2, etc with a micro-TCD. Lowest I have gone is around 50 ppm and even then the peak is very small.

Do you have an estimate of your signal to noise on the small area count peaks you are seeing.

Best regards,

2 posts Page 1 of 1

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