Chromatography Forum

Hi

i'm using a GOW-MAC TCD with a Porapack-Q column. (GAS CHROMATOGRAPHY)

I have a sample only composed by H2 and CO2, i prepare it manually admiting 90% and 10% respectively using their parcial pressures, in a previusly vacuumed reservory.

First i inyected the sample to the GC and it showed me a saturated peak for H2 as shown in the image, and of course i couldn't quantify it properly.

To correct this, i decided to dilute the gas with the same carrier i was using (Ar). I diluted it by 4, and i was able to watch the whole H2 peak, but then the area of each gas was 95% and 5%, so i suspect the area of CO2 is subestimated. And my lab partners also tell me that could happen.

So do you have any recomendations about how can i correct this?

i know there are some tricks like play with the attenuation, or maybe measure it without dilution to know the CO2, and then dilute it to see the h2 having in consideration the dilution factor. But i'm still thinking in this idea... can you help me please to resolve it?

thx

update: recently i have heard about the response factor of gases for GC, is this the solution?

How are you making your injections? Gas-tight syringe? Rotary valve with a sample loop? What is the volume of your injection?

How exactly, are you preparing your standard? How sure are you that you are making your standard correctly?

For instance, if I tried to make this standard with a Retek air-sampling cannister, I might evacuate the container, then fill to 20 psig with H2. If I add CO2 to make 21 psig, I get 95:5. If I add enough to make 23 psig, I get 87:13. I would argue that the gauge is not really accurate enough to make that sort of determination.

The more you can provide about what you are doing, the better the group can help you.

Surely you need to calibrate the peak area against concentration - with a TCD you cannot simply calculate composition from raw peak areas.