Accurate measurement of residual dipolar couplings in anisotropic phase.

The determination of residual dipolar couplings (RDCs) by quantitative J spectroscopy methods such as Heteronuclear Single Quantum Correlation with Phase Encoded Coupling (HSQC-PEC) is prone to systematic errors that may be caused by differential attenuation during the conversion of orthogonal density operator components into observable terms. The attenuation may be caused by miscalibration of radio-frequency pulses and by relaxation effects. A simple method is presented that allows one to remove most of these systematic errors without losses in sensitivity or resolution.