In addition, we demonstrated that the conversion process is strongly affected by the presence of N nuclei, which make the pH 2 -nascent protons in the complex magnetically inequivalent. This effect is of great importance for polarization transfer experiments at ultralow fields, where the signal enhancement decreases when the isotopic abundance of N nuclei is increased. The reason is that the limited source of pH 2 -derived polarization is exhausted upon polarization transfer to N nuclei. Thus, we can conclude that spin order conversion processes from pH 2 to oH 2 , and within the triplet manifold of oH 2 are an important for the success of PHIP and SABRE experiments. We believe that consideration of these processes and corresponding optimization of experimental parameters (concentrations, extent of isotopic labelling, pH 2 pressure, parameters of NMR pulse sequences) can significantly improve the signal enhancements that can be achieved by PHIP and SABRE.