Chromatography Forum

Hello,

another update in the odor-story.
I was trying to add 246_Tribromoanisole to our routine methode. When injecting (SPME) a high standard simply spiked in mQ there is no problem detecting it. but when I apply the regular sample prep I can't find 246TBA anymore.
I managed to trace the problem to the 25µl 1M NaOH that is added to 10ml of sample in order to get a better peak chape for 2-MIB.

Apparently 246TBA breaks down, or is unable to be trapped on SPME when the pH is high.

On the image below you can see:
-> a 246TBA standard in the presence of NaOH
-> the same 246 TBA standard without NaOH
-> a mass spectrum of the peak at 15.69min in chromatogram 1 (this is not 246TBA)
-> a mass spectrum of the peak at 15.76min in chromatogram 2 (this is 246TBA)

please note that the scaling is different for both peaks.



Can anyone explain to me why I don't see this effect with 246-Trichloranisole? I'm perfectly able to see TCA at 0.02-0.05ng/l and the 246TBA peaks shown above are about 10-20ng/l.

TBA should be no more reactive toward strong base than is TCA.

TBA is quite a bit heavier than TCA (Br = 80, Cl = 35.5 and there are 3 each) so I'd expect that it will be more difficult to collect TBA on the SPME fiber than it is TCA. In fact, that's what I see as well. It's been a long time since I had to quantitate TBA so I don't recall exactly the detection limit that I was able to obtain in my hands. I want to say that it was like 1 part-per-trillion TCA and 8-10 parts-per-trillion TBA but I can't swear to it. I can smell them both in the olfactory port at concentrations where I don't see a peak in the mass spec. detector.

I agree with it beeing less 'sensitive'. The under the same conditions,without NaOH TCA is a lot easier than TBA. But as you can see by the chromatograms, once NaOH is added TBA is gone