LC - ¹³C NMR utilizing dynamic nuclear polarization (DNP) for signal enhancement

Abstract

<p>The primary difficulty for successful LC .13C NMR (whether 1H or 13C) is overcoming the relatively low sensitivity of NHR as a chromatographic detector. For the 1H nuclide this is much less of a problem; the sensitivity ;s approximately 6000 times more sensitive than that of 13C nuclei. For this reason, much of the literature focuses on LC .1H NMR. To ever successfully realize LC .13c NMR, it is mandatory that an augmentation of 13C signal intensity must be effectuated to overcome this sensitivity deficit (- three orders of magnitude). To satisfy this requirement, our laboratory has utilized dynamic nuclear polarization (DNP) to ameliorate these otherwise weak or non-existent signals. For favorable molecules, sensitivity recoveries of up to two orders of magnitude have been developed. This improvement (relative to 'H) narrows the sensitivity gap between 'H and 13C NMR detection of chromatographically separated analytes. Despite the fact that relativeLy large injection volumes were required in most LC experiments, the wealth of structural information inherent to 13c NMR justifies any attempt to successfully couple nuclear magnetic resonance to liquid chromatography.</p> <p> In addition, DNP was utilized in a series of SLIT and LLIT experiments where a test mixture was recycled through a NMR spectrometer. Results indicate that 13c spectra were obtained with a significantly higher signal-to-noise ratio in a shorter amount of analysis time relative to experiments where DNP was not employed for signal enhancement.</p>