Abstract
A new NMR experiment (Destruction of Interfering Satellites by Perfect Echo Low-pass filtration, DISPEL) is introduced that facilitates the analysis of low-level components in high dynamic range mixtures by suppressing one-bond 13C satellite signals in 1H spectra. Since the natural abundance of 13C is around 1.1%, these satellites appear at 0.54% of the intensity of a parent peak, mimicking and often masking impurity signals. The new experiment suppresses one-bond 13C satellite signals, with high efficiency, at negligible cost in signal-to-noise ratio, and over a wide range of one-bond coupling constants, without the need for broadband 13C decoupling.
Highlights
Is a powerful emerging tool in the analysis of low level impurities, giving highly sensitive and well-resolved spectra.[2−6] Recent experiments have made the use of 19F NMR even more attractive by allowing uniform quantitative excitation of its wide chemical shift range[7,8] and suppression of 13C satellite signals.[9]
The much smaller secondary isotope effects on the chemical shift mean that long-range 1H−13C couplings cause few if any problems
A subtler problem is that the secondary isotope effect on the proton chemical shift means that the decoupled signals from 13C isotopomers have slightly different chemical shifts from those of 12C isotopomers which slightly broadens the bases of the decoupled resonances
Summary
In the 1H spectrum of Figure 1b, obtained with the new one-bond 13C satellite suppression method, the absence of the 13C satellites makes it straightforward to identify those signals that do not originate from omeprazole. The Destruction of Interfering Satellites by Perfect Echo Low-pass filtration (DISPEL) experiment facilitates quantification of dilute components by suppressing the interfering satellite signals, at the price of a small additional uncertainty, typically of the same order as the contribution of the spectral noise, due to differences in relaxation times. The new method introduced here is straightforward to implement and offers the possibility of acquiring clean 1H spectra, free from 13C satellites This will greatly facilitate both the analysis of low level impurities in the presence of strong signals and the measurement of 1H spectra in protiated, as opposed to deuteriated, solvents, while retaining the high resolution and sensitivity of the conventional 1D 1H experiment.
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