Direct polarization of 17O in 60/30/10 (v/v) d8-glycerol/D2O/H2
17O using 35% labeled 17O water and 40 mM electrons, using 9 W of microwave power. Radicals are arranged from highest enhancement to lowest, with trityl (16 scans, ~2 minutes), mixture (64 scans, ~8 minutes), TOTAPOL (608 scans, ~60 minutes) and SA-BDPA (1,664 scans and ~180 minutes), and, the microwaves off x15 (6,646 scans, ~12 hours) spectrum from the trityl sample. NB: Enhancements and uncertainties in Table 1 were determined by acquiring an on/off signal on the same sample; the bottom trace in the figure is the off spectrum for the trityl radical and is included here for reference purposes.