I've started working with a GC to measure hydrogen gas in closed system.
Before I made a calibration with 10% H2-90% N2, which worked fine. However, with the new calibration gas (80% H2- 20% N2) I'm encountering issues. The characteristic H2 peak around +/-0.84 min is preceded by a smaller peak (See picture).
When I measure in my closed system (bottles with septum) this preceding 2nd peak is no longer there. But the values that I calculate with the calibration make no sense (my H2 concentration should decrease over time, instead my closed systems show hydrogen concentrations higher than 80%).
Can I unify these 2 peaks? Is it both showing H2?
Some extra info:
- Shincarbon column (Shincarbon-ST 50/80 Stainless steel 2.0 m x 3.0 mm)
- Carrier gas = helium
- Column = 40°C
- Total flow = 35 mL/min
- DTCD = 150°C
- Current = 100 mA
Thanks for any ideas
Unify, no. See the up/down trace? That is from a pressure change in the flow. That looks like an injection peak, not a sample peak (0.8). Injectors cause a pressure pulse in the flow because they first make and then break connection to the column flow to introduce the sample. The off-scale peak at ~ 2 minutes, is that Nitrogen? Hydrogen usually shoots right through those columns so may not be very useful for quantitative work (poor selectivity).
Dear Janne,
As mentiond by William, first peak is responsible for the injection.
If there are no addtional peak, the second peak is responsible for both N2 and H2.
if you look at carefully, you can see small split in 2nd peak in 2nd chromatograph. this is an evidence for poor seperation of two gases.
If possible Please set colum temperature about 30 C for better seperation.
Piyal Aravinna
Thanks for all the suggestions:
William Letter : The peak at 2 minutes is indeed nitrogen.
A. G. Piyal Aravinna: The small split in the 2nd peak will be a small contamination of O2
David Poulsen De Sousa
: No ventI am quite convinced that the peak at 0.8 minutes is a hydrogen peak for 3 reasons:
1. I'm following recommendations from Shimadzu (picture GC1) to measure this hydrogen gas.
2. I also did not encounter this problem when measuring the 10% H2-90% N2 mixture. This just gave 1 clear peak at 0.8 min which obviously was hydrogen, since in the experiments this peak exactly behaved as expected.
3. In the samples that are flushed with 80% H2, there is also no up/down trace (picture 2), but just 1 clear peak...
I will start by using some new settings to get a better seperation, but more recommendations are more than welcome.
Thanks,
Janne
Dear Janne,
Even though you have changed H2 from 10% to 80%, shape and size of first peak of both chromatogram is same, so that it could be peak of injection. Otherwise there should be changes in director response.
To solve the problem, could you run H2 sample along.
Piyal Aravinna
A. G. Piyal Aravinna : the "picture 2" depicts a chormatogram of a sample that is flushed with the 80%H2-20% N2 mixture.
For clarity, I'm attaching a chromatogram of the 10% H2-90% N2 calibration. You can clearly see that the response is lower in this one.
Janne
Looks like poor separation and H is eluting at the injection void time (co-elution). It would be nice to see the second large peak injected on-scale for comparison. A huge change in the amount of Hydrogen introduced is only resulting in a small response change (not as expected). As noted earlier, the method you have selected is not selective for Hydrogen quantitation as it is poorly retained on the column. A basic fundamental of chromatography is that we must have adequate retention on the column to demonstrate the method is selective for the sample.
Hydrogen in often included in example sample mixtures for GC application notes (as a reference), but that does not mean you should use the application note as written for actual measurements.
Yes, latest chromatograph is clear. I agree with William.
In addition, why don't you try directer respons and seperation @
1 oven temperature at 30 C
2 with carrier Gas Ar
Piyal Aravinna
W shaped hydrogen peaks are the result of interactions between the carrier gas (helium), hydrogen from the sample, and TCD detector. The appearance of W shaped peak depends on the type of TCD detector. See HP application note . To prevent the formation of W shaped hydrogen peak and to retain high sensitivity of TCD detector use as a carrier gas mixture of H2/He. (8.5%H2 in He).
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