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How can a gas chromatography with flame ionization detection (GC-FID) be used to identify a liquid solvent that decomposes at its boiling point like DMSO? In a solution with other higher boiling solvents, DMSO shows some stability at elevated temperatures but when finding its retention time for the given column, a pure sample would be injected at highly elevated temperatures, temperatures beyond its boiling and decomposition temperature so how will its retention time peak be resolved?

Full disclosure, I am separating a mixture of N-methyl-2-pyrrolidone and DMSO and I need a way to detect both of these solvents in a GC-FID.

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    $\begingroup$ The question is, if GC is a good method for thermally instable components. $\endgroup$
    – Poutnik
    Jun 24, 2022 at 7:16

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In gas chromatography there is a common misconception that separation occurs on the basis of boiling points (it does but only on specific traditional columns). You don't have to be above the boiling point of the analyte in GC. The main condition is that you must be above the dew point of the least volatile analyte during the chromatography run. The problem is knowing the dew point. Also GC gases are strictly oxygen and water free so decomposition near the boiling point may not be an issue.

A formal method for determining inlet temperature is to inject the same standard at various inlet temperatures and plot the response. You might see a peak like response i.e., at low/high temperature inlet response is low but somewhere in the middle the response is high. If there is degradation you will lose response.

As always, best temperature and sample degradation is a trade-off. Literature survey must be done to see what temperatures people use for your analytes. DMSO is not a new compound for GC.

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