13C-Formate as an indirect low-temperature 1H lineshape polarimeter

• Highly polarized [1– 13 C]formate acts as a thermometer of spin temperature. • 13 C lineshape asymmetry increased with increasing 1 H spin polarizations. • The approach is sensitive to 1 H spin polarizations approaching ∼100 %. 1 H polarization quantification is important for dissolution-dynamic nuclear polarization ( d DNP) but can be cumbersome due to the requirement of acquiring thermal equilibrium signals and measurements that are complicated by large background signals. 1 H nuclear magnetic resonance (NMR) spectra can also be deleteriously influenced by line distortions linked with radiation damping from 1 H DNP and cannot be used for accurate calculation of 1 H polarization. Determining 1 H polarization via immediate 13 C lineshape analysis of a simple molecule removes such complications. We present 13 C-sodium formate as a straightforward system for indirect 1 H polarimetry. The 13 C NMR spectra acquired under d DNP conditions have distinct features that are readily reproduced with 13 C lineshape simulations. 1 H polarizations built-up during 1 H DNP were indirectly inferred by fitting simulations to 13 C lineshapes. We provide the MATLAB scripts used for 13 C lineshape analysis in order that the method can be readily implemented in other laboratories.