The resulting single-shot spectra from the SHEATH-ULF sequence are shown by the blue lines in Fig. ). In the left panel, no ZF delay time (τ = 0 ms) was applied prior to the 90-degree N pulse, which was used for for optimal readout of the 15 N NMR signal. A characteristic 1:3:3:1 multiplet 33 is observed, arising due to the J-coupling of 15 N with three equivalent protons. In the right panel, the proton NMR signal is presented, acquired under parameters optimized for proton readout: a delay time of τ to 0.15 ms followed by a 90degree ( 1 H) pulse. This results in a doublet, caused by the J-coupling with the 15 N nucleus.