A prototype d DNP polarizer "Alpha Polarizer" developed by Bruker Biopspin ® was used to hyperpolarize the samples. 100 µl of HP1 or HP2 was first frozen by freezing individual 10 µl drops in liquid N 2 . The resulting beads were transferred into a PEEK sample holder. In addition to the analytes, the sample holder was also loaded with 10 beads of 10 µl 3 M ascorbic acid dissolved in D 2 O, as well as an additional 30 mM of sodium ascorbate to the dissolution heating module containing the hot solvent, in order to reduce the polarization loss due to paramagnetic relaxation . The sample holder was placed in the liquid helium bath of the cryostat and the temperature was lowered to 1.2 K by pumping the cryostat to 0.65 mbar.