DETERMINATION OF THE APPARENT TRANSVERSE AND AXIAL-DISPERSION COEFFICIENTS IN A CHROMATOGRAPHIC COLUMN BY PULSED-FIELD GRADIENT NUCLEAR-MAGNETIC-RESONANCE

Pulsed field gradient nuclear magnetic resonance permits the direct determination of the coefficient of apparent dispersion of a solute in a chromatographic column. Axial and transverse dispersion coefficients can be measured independently as a function of the flaw velocity of the mobile phase. Experiments have been carried out using water as the mobile phase, porous C18 silica as the stationary phase, and water as the probe (self-dispersion). The results are reported and compared to similar ones obtained previously by various authors, using conventional chromatographic techniques. The NMR method shows potential for the investigation of the structure and homogeneity of the packing of large diameter columns for preparative chromatography. It permits direct access to local values of these coefficients instead of measuring averages as classical methods do.