Hyperpolarising 13C for NMR studies using laser-polarised 129Xe: SPINOE vs thermal mixing

We have compared the efficiency of spin polarisation-induced nuclear Overhauser effect (SPINOE) and low-field thermal mixing (TM) for enhancing the 13C NMR signal by polarisation transfer from hyperpolarised xenon. In our experiments of TM, the carbon NMR signal was increased by up to a factor of 390, about five times larger than the maximum enhancement obtained using SPINOE in liquid hyperpolarised xenon. Moreover, we show that the enhanced 13C nuclear polarisation survives a solid/liquid transition, and the subsequent separation of the carbon compound from hyperpolarised xenon, thus opening the possibility of producing hyperpolarised carbon compounds for NMR applications in biological systems and materials science.