Chromatography Forum

Dear everyone,

sorry to bring trouble here, but I have run into trouble with hydrogen calibration using manual injection.
I am working on biofermentation producing hydrogen, and need to test the percentage of hydrogen in biogas. So first I need to calibrate the GC. I use three gas standards here: (10% h2,10%co2,10%ch4 and 10%n2, 60%argon); (25%h2, 25%co2, 25%ch4 and 25%n2);(100%h2). I use scotty 14 cylinder and attach an adapter to the cylinder valve. I draw 40ul standard gas out from each of the three standard gases by opening the cylinder valve and insert the gas lock syringe needle into the adapter. But the problem is: if the whole system is airtight, when you open the cylinder valve, the pressure will build up inside the adapter and it's not easy(maybe impossible) to make sure that the gas you draw into the syringe is atmosphere pressure(here the friction between the plunger and syringe barrel also counts).

The question is: how do I make sure that each time I am drawing the same amount of standard gas (here I am talking about not only the same gas VOLUME but also the same atmosphere pressure in the syringe!!). I need the gas volume to be 40ul to calibrate!!

Thank you so much. Hope someone can save my life.

Eric

If you fill the syringe to the correct volume with gas at a higher pressure than atmospheric, then withdraw the syringe from the adapter and briefly open the gas-lok valve on the syringe the excess pressure will bleed off. leaving the syringe filled at atmospheric. Or am I misunderstanding the problem ?

Peter

@peter Thank you so much for quick replying. My concern here is: if you open the gas-lock valve to release the excessive gas in the syringe, won't it be contaminated by air? Thank you.

Eric

Unless you are using a HID or using a TCD with nitrogen carrier your efforts to calibrate are worthless.

best wishes,

Rod

Hi Rod,

I am suing a TCD but the carrier gas is Helium.

Unless you are using a HID or using a TCD with nitrogen carrier your efforts to calibrate are worthless.

best wishes,

Rod

Peter,

You saved my life...

If you fill the syringe to the correct volume with gas at a higher pressure than atmospheric, then withdraw the syringe from the adapter and briefly open the gas-lok valve on the syringe the excess pressure will bleed off. leaving the syringe filled at atmospheric. Or am I misunderstanding the problem ?

Peter

Your results will not be linear in response using helium

best wishes,

Rod

Yes it's not linear. exponential curve works better...Still useful?

Your results will not be linear in response using helium

best wishes,

Rod

Try to research the response of hydrogen on a TCD using helium carrier. You will not be happy with the results.

best wishes,

Rod

You'd be better using a gas sampling valve surely? Flsuh with sample gas and inject at zero sample flow. It'll be prone to errors due to atmospheric pressure fluctuations but not nearly as much as using a syringe.