Protocol (a) in figure uses a conventional field-ramp procedure for singlet-to-magnetization transfer . This was performed as follows: Para-enriched H 2 was bubbled through the solution for an interval of duration τ B , in the presence of a static bias field of 50 µT, in order to separate the Larmor frequencies of the different isotopes, helping preserve the proton singlet order. The magnetic field was then swept linearly from ≃0 µT to ≃1 µT over a duration τ T , to induce the singlet-tomagnetization transfer. As shown in table 1, experimental optimization of the bubbling time (τ B = 7 s) and the transfer time (τ T = 90 ms) resulted in a 13 C polarization of p = 0.98% ± 0.04% for the [1-13 C, 2,3-d 2 ]-succinic acid reaction product. A representative spectrum for protocol (a) is given in figure . The moderate level of 13 C polarization level is not surprising, since the conventional field-ramp protocol is subject to interference from both deuterium quadrupolar relaxation and singlet-triplet mixing.