For the experimental implementation of protocol (c) we kept the STORM pulse parameters identical to protocol (b), but added a WOLF pulse with amplitude B WOLF = 20 µT and frequency ω WOLF /2π = 800 Hz during the hydrogenation interval. The WOLF pulse parameters were based on the analysis given in the supplementary information. The pH 2 bubbling period was optimized to τ B = 15 s for protocol (c). The resulting 13 C spectrum is shown in figure , which corresponds to a 13 C polarization of p =6.13%±0.07%. As highlighted in table 1, this represents a factor of 6 improvement over a conventional field sweep procedure.