I suspect I have some dissolved methane (and maybe propane) in my aqueous solutions. Please see attached spectrum (for both spectra: number of scans is 256; same receiver gain; same method; water suppression was poorer for my experimental sample). In green is my experimental sample and in red a control one with only pure water (red shows a few peaks which can only be some sort of contamination). If it was a liquid or solid species, I would buy a commercial standard and spike my NMR tube after acquiring the spectrum to see if a new peak(s) appears or the one I saw previously grows (confirming it's the same species).
Is this possible with gases? Should I simply add such gas in the headspace of the NMR tube, shake the contents for a while, and re-analyze?
On top of this, I'm of course performing all sorts of negative controls to make sure these putative gases don't come from a contamination and were indeed synthesised during my experiments (which is what I'm looking for).
Thank you,
Eloi
By the way, I did not add any internal standard to either tube. Will do soon.
Thank you Clemens Anklin
and Jp Wu,I should have specified that some of the gases I mentioned (methane for instance) are potential products of my experiments, so if I'm indeed synthesising them, that'd would be important. Hence, I don't want to/can't degas my samples.
My current conundrum is (1) making sure I correctly identify the peaks, and (2) confirm they are not external contaminations. A complete set of negative controls will help with (2), but I'm still not sure how to confirm the peak assignation. I guess I can only do this by ruling out competing explanations.
There should be no problem to "spike" the solution with additional gas (bubbling it through the solution or fill the space above the liquid and shake), we did this often with hydrogen or hydrocarbons. If you suspect methane as product, you can identify it by recording 13C since its shift is very characteristic (below 0 ppm). If the concentration is very low, you may use indirect detection.
Thank you all. I did a spike test finally by bubbling methane. The peak indeed grew, reinforcing the idea I had methane. GC-FID showed it is not methane though, although chemically similar. Currently investigating this further.
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