LowCOST-HSQC Variants for Fast-Pulsing High ω₁-Resolved 2D Experiments

The LowCOST-HSQC is a sensitivity-enhanced HSQC version that retains unused proton polarization for subsequent scans in correlations to low natural abundance nuclei like ${}^{13}$ C or ${}^{15}$ N. Together with fast polarization distribution via isotropic mixing, it allows the acquisition of fast-pulsing 2D experiments. We give a detailed introduction and comparison of three possible INEPT-type transfer elements for the LowCOST approach-the original LowCOST, the ZIP, and a specific TIG-BIRD element-and evaluate various variants of the LowCOST-HSQC.