I am using MS quadrupole for on-line detection of diluted gases e. g H2 during TPR H2. How can be MS calibrated for quantitative analysis of hydrogen? When I record signal (torr) for 10 % of H2 in Ar, m/z=2, the signal is not twice a higher compared to the signal of 5 % H2/Ar. The difference is only 1/5 of the signal. Why? I supposed that signal should be linear (concentration/partial pressure vs time).
Quantitative mass spec... not easy! First make sure you not looking at logarithmic scale in the MS software (yes I've made that mistake). But the amount of ionization (therefore signal) is not equal for all gases and mixtures. You will have to try different filament currents for example to make sure everything is being ionized (easier to ionize 5% than 10%).
You can try quantifying the peaks by comparing integrated peak areas from your sample with a standard material such as silver oxide using the same gas concentrations, flow rates etc, but to make it as accurate as possible you need the same amount of reducible oxide because of he non linearity of the signal. So a few experiments adjusting the amount of reference oxide until peak heights match.
My best recommendation is to reach out to the MS manufacturer and their application support team to ask for guidance.
A TCD is easier if you don't have multiple gases involved (ignore the carrier gas).
Thank you for the answer. I am not in log scale. I would redifine the question to: What is the effect of other gases in the mixture (QMS) on the signal (torr) of one component from the mixture. Example: I have 5 % H2 in Ar and 5% H2 in Ar+He. The total flow is the same for both cases. Why the signal for H2 (m/z=2) is not the same for both cases? Why change of the Ar into He (without change in H2 concentration) affects the signal?
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