Determination of the temperature dependence of the dynamic nuclear polarisation enhancement of water protons at 3.4 Tesla.

It is shown that the temperature dependence of the DNP enhancement of the NMR signal from water protons at 3.4 T using TEMPOL as a polarising agent can be obtained provided that the nuclear relaxation, T(1I), is sufficiently fast and the resolution sufficient to measure the (1)H NMR shift. For high radical concentrations (∼100 mM) the leakage factor is approximately 1 and, provided sufficient microwave power is available, the saturation factor is also approximately 1.