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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: Cantacoxinha on November 14, 2020, 11:01:43 AM

Title: 13C/12C quantitation by NMR?
Post by: Cantacoxinha on November 14, 2020, 11:01:43 AM

Food adulteration can be determined by measuring the ratio of ²H vs. ¹H atoms at the site-specific portion of an analyte. It is done by measuring both spectra and then calculating the ratio. Sometimes an additional ratio of ¹³C vs. ¹²C is determined by NMR, also to check for adulteration. What I don't understand here is:

1) how is the quantity of ¹²C determined, if ¹²C is NMR inactive?

2) how in the world is ¹³C quantified by NMR, if carbon spectra are decoupled and thus "unintegrable"??

I'd be grateful if somebody could explain this.

Title: Re: 13C/12C quantitation by NMR?
Post by: Babcock_Hall on November 14, 2020, 02:41:25 PM

I agree that one cannot observe C-12 nuclei by NMR.  Can you propose any method, perhaps an indirect one?

Title: Re: 13C/12C quantitation by NMR?
Post by: Corribus on November 17, 2020, 11:45:53 AM

You can determine the isotope ratio by nmr.

See, e.g., https://pubs.acs.org/doi/10.1021/acs.analchem.7b02473

(Pironti, et al. Anal. Chem. 2017, 89, 21, 11413)