The conversion of proton singlet order into 13 C magnetization is a crucial step. Methods exist for implementing this transformation either in the high magnetic field of an NMR magnet, or in low magnetic field. Low-field procedures are preferred for real-world applications, since they allow the use of relatively inexpensive, compact, and mobile equipment . Recently, purified solutions of highly polarized [1-13 C]-fumarate have been produced using a low magnetic field sweep for singletto-magnetization conversion . However, [1-13 C]-fumarate is a favourable case since it has a very simple spin system, containing only three coupled spins-1/2.