second level calib. for only one component in 6890 RGA

[avrc]

Hello everybody,

I am working on a 6890 RGA. Is it possible to do a 2nd level calibration for hydrogen alone? Because, I have only one calib. gas mixture and the hydrogen conc. in it is 80%. I get an error of 2 to 3 percent while using this calib. table. So I want to use 100% hydrogen as another standard, since my samples have conc. around 90 to 95 mole percent.

Please give me your suggestions, thank you all!

[Les]

Dependent on your software, adding more levels would help with H2. I run Turbochrome and use 30,50,70, & 90% cal levels. Also dependent on the RGA, the hydrogen response may not be linear. Therefore necessary to have more levels. I have used 100% hydrogen as a check of the injection system, but since that wasn't a "calibration standard", I didn't use it as one. But I don't see any problem in using it. My RGA system from AC controls measures propane thru pentane components on FID. These are 1 level cals with a 3% std. The system has a fairly linear response on TCD for H2 from 2% to 90%. Now the Perkin Elmer is a different animal. The TCD hydrogen is non-linear.

[chromatographer1]

If you are using bottled hydrogen and have a purity certification from the supplier I would believe that qualifies the cylinder contents to be used as a standard, although I should require a test of that particular cylinder ALONE, not merely a certification of the bulk gas from which the cylinder (bottle) was filled, to be a standard, even if it is 99.99 % hydrogen.

I would also not use the last 10-20% of the cylinder contents as a std.

[avrc]

Thank you very much, Les & chromatographer1 for your inputs.
I am using a Agilent 6890 RGA and I am not getting my methane peak. I am getting 79% N2 and 20% O2 (satisfactory separation) while injecting air and so I think the mol.sieve column is OK. I think there might be some problem in my valve switch-over timings. Can I use FID to detect methane? Since O2, N2 are not going to be detected on FID and I dont have CO in my sample, the peak I get after C5/C6+ peak, I assume, to be methane alone. And I am thinking about calibrating for methane using that peak from FID (and also the next peak in FID I am thinking to use for calibrating C2, since I dont get ethylene in my samples)

Am I right in doing this?

Your comments please.