THE CHANGE OF PRESSURE-DROP DURING LARGE-SCALE CHROMATOGRAPHY OF VISCOUS SAMPLES

The variation of the inlet pressure during the injection and the eluti on of a band of a viscous compound, or pressure-drop profile, was calc ulated in overloaded elution chromatography, assuming a significant di fference between the viscosities of the solvent and the pure solute. T he viscosity of the mixture was calculated using the Grunberg-Nissan e quation. By means of the numerical integration of the mass balance equ ation, the concentration profile along the length of the column was ca lculated. Then, using the instantaneous concentration profile to deriv e the local viscosity, hence the local pressure gradient, the pressure drop was determined by integrating the local pressure gradient along the column. The change of pressure drop calculated is significant only when the concentration of the injected sample is very high. If a dilu te sample is injected, even large sample volumes will not really chang e the pressure drop. The maximum pressure drop observed in each case i s practically independent of the absorption isotherm. The only determi ning factors are the solute concentration in the sample, the amount of sample injected, and the solute diffusivity.