To compare the C 𝑇 1 times of the purified and control samples, a modified version of the experiment was used, where instead of applying a 90° flip angle pulse, 10° flip angle pulses were used to excite the C signals for acquisition once every 5 s. By using a small flip angle pulse, the hyperpolarization was not significantly perturbed for each signal acquisition, and the longitudinal relaxation time (𝑇 1 ) of the carboxylate C spins could be measured directly from the signal decay. The results of this experiment are shown in Fig. . The C 𝑇 1 was measured to be 86 s for the control sample, and 71 s for the purified sample. This small difference is likely due to the samples containing different concentrations of paramagnetic oxygen; the control sample was thoroughly oxygen degassed, but the aqueous solvent used to redissolve the purified fumarate was not. These 𝑇 1 values are similar to those reported in the literature .