Peak parking method for measurement of molecular diffusivity in liquid phase systems

The combination of series of measurements of band broadening made with the peak parking (PP) method, using successively an open capillary tube and a HPLC column, gives a convenient procedure for the measurement of the molecular diffusivity (Dm) of compounds in solutions, of their axial dispersion coefficient (Dax,m) in chromatographic columns, and of the tortuosity or obstructive factor of the column bed. The molecular diffusivity measured for benzene in methanol was in excellent agreement with literature data. The ratio of the axial dispersion coefficient to this diffusivity gives the obstructive factor (γm) of the packed bed, which was 0.74 for the column used. The values of Dm in other solutions were obtained from the Dax,m values measured by the PP method, by correcting the Dax,m values with the γm value. The Dm values determined by this method were in good agreement with those previously reported or estimated using literature correlations. These results showed that the PP method is effective for the experimental measurement of Dm.