Spatially encoded polarization transfer for improving the quantitative aspect of 1H–13C HSQC

Peak overlap hampers quantification in one-dimensional (1D) ¹H NMR. 2D ¹H -¹³C HSQC spectrum provides resolution superior to 1D ¹H NMR. However, quantifying the components in a complex mixture with HSQC is not straightforward as in 1D ¹H NMR. Quantification using HSQC could open up new avenues for studying metabolism. The variations in ¹H–¹³C scalar couplings, T₁, T₂, and pulse imperfections contribute to this problem. Although T₁ and T₂ can be suitably chosen to minimize their deleterious effects, the differential polarization transfer for different resonances owing to large variations in ¹H -¹³C couplings does not allow the cross-peak intensities to be directly correlated to the quantity of metabolites. Existing approaches are time-consuming. We show that spatial encoding of the polarization transfer delays in HSQC using sweep frequency pulses in the presence of a magnetic field gradient allows one to have a transfer of polarization from ¹H to ¹³C insensitive to variations in ¹H -¹³C couplings improving the quantitative aspect of HSQC. Comparisons to other QHSQC and perfected HSQC variants are also provided.