Measurement of the diffusion coefficient of a model food dye (malvidin 3,5-diglucoside) in a high pressure CO2+methanol system by the chromatographic peak-broadening technique

The accurate determination of the diffusion coefficients of solutes in supercritical solvents is a prerequisite for the modeling and design of extraction processes. At present, reported data on the diffusion of polar solutes in the system CO2+methanol at high pressure is scarce. In the work described here, malvidin 3,5-diglucoside was chosen as a representative example of anthocyanin compounds (natural food dyes). The diffusion coefficient of this compound was determined using a chromatographic peak-broadening technique. The effect of the amount of methanol in the solvent has been analyzed and the results show that a decrease in the diffusion coefficient occurs as the amount of methanol increases. This behavior has been attributed to the formation of solute–methanol clusters. Finally, the results obtained have also been correlated with temperature, solvent density and viscosity, with the best fit found in the correlation with density.