Chromatography Forum

Hi all

I'm using a GC for a school project. We made a small reactor that produces hydrogen gas from the methanol steam reforming process (methanol + water = hydrogen + carbon dioxide). We collected this gas mixture and now we want to analyze it to see if there is hydrogen. I know the mixture may contain hydrogen, oxygen, nitrogen, carbon dioxide, carbon monoxide and water vapor.

What I need is the correct specified injector temp, oven temperature, temperature profile and flow rate for analyzing hydrogen in a GC. I'm wondering if anyone knows anything about the correct specifications, or where I might be able to find these correct specifications.

I am using a thermal conductivity detector and I'm using a 5 angstrom packed column with helium as the reference and carrier gas. Any help is much appreciated!

First help:

Don't use helium as the carrier or reference gas. Use nitrogen. Helium will not give you linear response and as the hydrogen concentration increases the response will go negative in comparison to the response at lower (<7%) concentrations. The response will be linear and orders of magnitutde more sensitive if you use nitrogen as carrier. Not a choice, a mandate. Argon carrier is a second choice.

Second help:

You can use any temperature below 100°C but ambient is fine. Even using higher temperatures up to 60°C is good. Higher the temperature, the less separation from helium and the other fixed gases.

Third help: isothermal is suggested to be the best oven program.

Fourth help:

Water and carbon dioxide will be highly retained on the 5A mole sieve column. You will need to bake the column at 200°C for a few hours to remove these sample components, although you should be able to inject many samples before the performance of the column is degraded noticeably. Any excess water or other fixed gases that is normally trapped on the 5A if injected in excess will produce a non-reproducible peak, usually tailing in form.

Fifth help:

Elution order: helium, hydrogen, oxygen, nitrogen, methane, carbon monoxide, carbon dioxide. Any branched hydrocarbon (isobutane or higher) will elute with minimal retention. Isobutane elutes before oxygen. Others may elute later in unexpected places, varying according to your analytical conditions.

I have examples of fixed gas analysis to share with you if you will send me your email address.

best wishes,

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5459 fax
rodney.george@sial.com