Quantification Studies in Continuous-Flow ¹³C Nuclear Magnetic Resonance Spectroscopy by Use of Immobilized Paramagnetic Relaxation Agents

Abstract

Different types of immobilized free radicals as well as immobilized paramagnetic gadolinium(III) complexes were synthesized and used as relaxation agents to shorten the spin−lattice relaxation times T1 of analytes in quantitative continuous-flow 13C nuclear magnetic resonance spectroscopy (NMR). The immobilized paramagnetic relaxation agents were characterized with electron paramagnetic resonance spectroscopy (EPR) and extended X-ray absorption fine structure spectroscopy (EXAFS). With these types of paramagnetic relaxation agents, it was possible to obtain a 4-fold increase in signal-to-noise ratio per unit time, and an almost quantitative NMR spectra in continuous-flow 13C NMR spectroscopy could be acquired with this method.