You mean conversion in the sense of the extent of reaction?

If your system is simple enough, that is possible. Gas chromatography becomes a requirement if your reaction mixture gets complex which would result in the mass spectrum becoming an uninterpretable forest without chromatographic preseparation.

Thank you, Jurgen, for your answer.

Yes. I mean the extent of reaction. I wanted to know whether is it able to find percentage of ethanol conversion in my reaction from mass spec.

Well, like in the combined GC-MS you need a calibration so that you can convert spectral intensities to concentrations.

If your mixture is simple enough, you can do without the GC, but if you have all sorts of catalytic admixtures hovering around, the plain mass spectrum will be too complicated.

Hi, I do not have access to a GC—only a mass spectrometer is available. I am currently working on the dehydration of ethanol to ethylene. In my setup, ethanol is first vaporized and then passed over a catalyst. However, I’m encountering difficulties in obtaining consistent peak area readings, as the signals fluctuate due to the vapor-phase nature of ethanol. I suspect there may also be other products forming in addition to ethylene.

For the main reaction, you can probably do it without GC, then. If you have fluctuations, you would have to question whether it is an actual gas phase fluctuation effect or maybe a detector oversaturation; in that case, playing e.g. with the filament settings (assuming your MS has an electron impact ionizer) might be a good idea.

Regarding a side product analysis, you probably will into the signal forest problem discussed above.

Thank you so much for sharing your ideas.