Ultraclean Pure Shift NMR Spectroscopy with Adiabatic Composite Refocusing Pulses: Application to Metabolite Samples

Abstract

AbstractIn Pure shift NMR (pure shift yielded by chirp pulse excitation (PSYCHE)) Sideband Averaging by Periodic PHase Incrementation of Residual J Evolution (SAPPHIRE) has proved to be a very useful technique for obtaining clean high‐resolution NMR spectra; SAPPHIRE suppresses homo‐decoupling sidebands resulting in high‐quality pure shift spectra. As a consequence, it enables circumventing dynamic range problems for complex mixtures having wide range of concentrations of constituents; in conventional PSYCHE spectra, the signals of low concentration constituents may get masked by the sidebands. However, the SAPPHIRE‐PSYCHE scheme is very sensitive to pulse/power calibrations and does not perform well for miscalibrations. In this background we propose here an improvement employing adiabatic composite refocusing pulses (ad‐SAPPHIRE‐PSYCHE) which has enabled us to obtain ultraclean pure shift NMR spectra with high resolution. The resulting improvements with the new scheme have been demonstrated on metabolite samples, honey and peppermint oil, and we believe that this will become routinely usable in commercial environments using autosamplers and with technically not‐so‐well trained researchers.