Fast Quantitative ¹H–¹³C Two-Dimensional NMR with Very High Precision

Abstract

Quantitative analysis by nuclear magnetic resonance (NMR) requires highly precise measurements to achieve reliable quantification. It is particularly true in (13)C site-specific natural isotope fractionation studied by nuclear magnetic resonance, where the range of values of (13)C isotopic deviations at natural abundance is highly restricted. Consequently, an NMR method capable of measuring δ(13)C ‰ values with a very high precision (a few per mil) is indispensable. This high degree of precision has already been achieved by one-dimensional (13)C acquisitions; however, this approach is limited by peak overlaps which reduce the precision of the isotope content determination, even for certain small molecules. It is therefore necessary to extend this promising methodology to a higher dimensionality. In this context, this paper aims at determining conditions that allow the achievement of two-dimensional (2D) (1)H-(13)C heteronuclear experiments with a precision of a few per mil in a reasonable time. Our results demonstrate that a high precision (repeatability of 2 per mil) can be reached with the (1)H-(13)C HSQC (Heteronuclear Single Quantum Correlation) experiment, thus satisfying the conditions needed to perform (13)C isotope analysis by 2D NMR. We also consider the impact of several approaches which have been proposed to reduce the duration of heteronuclear 2D experiments. Two of these common time-saving strategies, spectral aliasing and linear prediction, are fully compatible with the high-precision requirements of isotopic NMR, while a third one, nonuniform sampling, leads to dramatic precision losses. In conclusion, this study demonstrates the feasibility of very precise 2D NMR measurements and opens a number of application perspectives.

Fractionation in position-specific isotope composition during vaporization of environmental pollutants measured with isotope ratio monitoring by 13C nuclear magnetic resonance spectrometry

“…The same approach could be extended to other type of transformation (biotic or abiotic). Improvements in sensitivity recently proposed include using modified NMR pulse sequences, exploiting polarization transfer (Thibaudeau et al, 2010) and 2D NMR (Martineau et al, 2013). Such developments, associated with the continuous improvement of sensitivity of the NMR spectrometer should bring down the amount of material required by 10e15 fold in the near future, i.e.…”

Resolution‐enhanced 2D NMR of complex mixtures by non‐uniform sampling

“…Resolution‐enhanced NUS will offer a more complete analysis of biological systems, especially in metabolomics applications, for which conventional 2D spectra suffer from extensive overlap . It could also be interesting to improve the results from recently published studies by taking advantage of the conclusions of the present paper . Finally, the increase in resolution could also be compared or combined with other time‐reduction methods such as ASAP HSQC for the HSQC pulse sequence or covariance for the TOCSY spectrum …”

Quantitative NMR Studies of Multiple Compound Mixtures

“…Therefore, in some cases, it is necessary to adopt 2D qNMR for quantitative analysis. For example, Martineau et al [178] employed fast quantitative 1 H-13 C HSQC to determine ibuprofen. Likewise, a quantitative 2D COSY has been used to identify and to quantify pharmaceutical excipients cyclodextrins in plasma medium [190].…”