ISOtope

[meillid]

Hi, I have new problem. I try to use D8-isotope nitrosamie as my internal standard. It was shock that the infusion of D8-isotope give me same spectrum as the d0 one. while consult with the supplier of D8-isotope, they said they sure that they give us the right thing and this compound is very stable. Is here anybody known anyway that associated with MS may cause the D8-isotope to lost its D8-isotope? welcome any sugestions.

[HW Mueller]

What is D8- and do-isotope nitrosamine? If you are talking about deuterium substitution of nitrosamin there is no surprise here. The two D(H) exchange very rapidly in a protic medium (H2O, alcohol, ....).

[meillid]

Hi, mueller, Thanks for the reply. Yes, I mean deuterium substitution of nitrosamine (N-nitrosodiethanolamine). I desolve it in ethanol. Yesterday, I called the manufacture about the possible D/H exchange of this compound, but they tell me that this coumpound is very stable and will not lose deuterium unless you break the molecules. I am prettly puzzle. How sure are you about the repid D(H) exchange of this compound? Is there any reference about this? I really appreciate your input!

[meillid]

By the way, do you mean the exchang happend in the sovent or in the ion source during ionization? Thanks.

[Kostas Petritis]

As the deuterium atoms are probably bonded in the carbon (i.e. 4 x CD2) there is no way they could have been exchanged in your solution or anywhere else.

Now why don't you see what you would expect, I have no idea (I can not think of a good reason why...).

[JA]

I was waiting for an expert to reply before I added a comment

We have made some deuterated metabolites at work and have quantified isotopic enrichment by ESI MS against unlabelled standards. While a distribution of C-D deuteration was observed, the D0 peaks have been minimal. I can't state that deuterium doesn't fall off (there appear to be articles covering its occurance at high temp/pressure) but my inclination is that is it unlikely. We put the distribution pattern down to the [imperfect] quality of the labelled precursors.

[meillid]

Hi, thanks all of you for reply. My director also show me a artical on RAPID COMMUNICATION IN MASS SPECTROMETRY (2004, 18, p37-42), which said that they were doing in-source deuterium labelling. I am not so convencinced since deuterium may majorly happened in solution because that they disolved in D2O before MS analysis. On the other hand, even there is some insource exchange, how can it reach 100% lost of deterium. I am still puzzle and persure answers for this puzzle. Thanks a lot.

By the way, when I just run empty MS (no infusion, no LC), I still detect pretty strong d0 NITROSAMINE signal even after 24hr bake out the instrument. Can the instrument be contaminated so much? what else to explain this? Did anyone ever run a empty MS? did you see any signals from this kind of experiment?

[JA]

Emily,
I don't have full access to the article you cited, however a quick look at the abstract and the structures of glyphosate and aminomethylphosphonic acid that the authors are working with makes me think their "triply deuterated [M-H]- ions" would be labelled at the labile positions on the nitrogen and oxygens. I'm in agreement with you that these could be readily exchanged in the sample solution.

Anyhow, I'm not sure how that helps you

Out of interest, when you spoke to the manufacturer, how did they test it to confirm D8 labelling?

[meillid]

they said they usually use GC-MS to test this compound. they use NMR confirmed the same lot material that they sent to me is D8 lableled. Thanks for reply.

[HW Mueller]

OK so you have a nitrosamine not THE nitrosamine (to me: H2N-NO). I also don´t see how you could loose all the D on the ethyls.
Maybe your MS is so badly contaminated with the H analog that the D analog is obliterated??