Dispersion in Chromatography Columns - Experimental Validation of the Van Deemter Equation > Page 80

Values for k' were obtained using the retention time of hexamethylbenzene as t0. Values for k'e (the excluded dead volume) were obtained employing the retention time of the completely excluded solute polystyrene (t(e)0) (Mol. Wt.83,000). t(e)0 was also employed for the measurement of the linear mobile phase velocity.

An example of the results they obtained for the solute benzyl acetate chromatographed with the solvent mixture 5.4%(w/w) ethyl acetate in n-hexane is shown in figure 19. The curve through the points is the fitted curve to the Van Deemter equation and the contributions from the multipath term, the longitudinal diffusion term and the total resistance to mass transfer, term derived from the curve fit, are included. It is seen that an excellent fit is obtained with the Van Deemter equation with an Index of determination of 0.999885. However, the results from testing all the data to each of the dispersion equations need to be known in order to identify the equation that, overall, shows the best fit.



Figure 19. Graph of H versus U for Benzyl Acetate (solvent 5.4%(w/w) ethyl acetate in n-hexane)