By Jianbo Hou
Quantitative 13C NMR spectroscopy provides a powerful tool to chemists for molecular structure elucidation and quantitation though often hampered by its low sensitivity. Here, we present the development of an NMR capability toward the generic application of quantitative adiabatic refocused insensitive nuclei enhanced by polarization transfer (QA−RINEPT) for fast and reliable acquirement of quantitative 13C NMR spectra routinely. Theoretical calculation enables identification of an optimized condition for quantitation, which maximizes the overall sensitivity gain meanwhile minimizing the non−uniformity of signal across the spectrum for a variety of commonly encountered functionalities, including aliphatic, amine, ether, aromatic and aldehyde groups. The non-uniformity in signal response due to polarization transfer can be compensated by calibrating the corresponding response factor to achieve more rigorous quantitation. Using a model compound mixture of small molecules, QA−RINEPT enables reduction of experimental cost by ~ 40× and generates quantitative 13C NMR spectra that show a good agreement with theoretical prediction. The capability uniquely combines sensitivity, spectral resolution and quantitation that finds broad applications from analyzing small molecules to polymeric materials.
Session #7: The tough stuff- measuring difficult things in soft materials