Chemical shift and magnetic susceptibility contributions to the separation of intracellular and supernatant resonances in variable angle spinning NMR spectra of erythrocyte suspensions

Factors contributing to the observation of two separate water resonance arising from erythrocyte suspensions under magic- and variable-angle spinning conditions were examined. By observing the 1H NMR spectra of different chemical species in erythrocytes at different spinning angles, two major effects of comparable magnitude were shown to contribute to the separation: 1) an isotropic chemical shift difference, and 2) a susceptibility difference between the intracellular and supernatant compartments. When the sample was spun at the magic angle, the susceptibility difference did not contribute to the separation. Use of different angles between the spinning axis and the main magnetic field provided a method for quantifiying the isotropic chemical shift and susceptibility differences between the compartments.