Chemical Shifts of Solutes in SCFs

In their study of SCF chromatography coupled to NMR detection, Braumann et al. noted an upheld shift of H NMR resonances as the CO2 pressure was 

The relatively small changes in chemical shift with pressure can be qualitatively explained in terms of changes in bulk susceptibility as most spectra in SCFs are obtained without internal lock. Large chemical shift ranges are a characteristic of metal NMR spectroscopy, and the changes observed on changing temperature, pressure or solvent are no more exaggerated in supercritical solvents than those observed with conventional solvents. 

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