Dispersion in Chromatography Columns - Experimental Validation of the Van Deemter Equation > Page 81

 

The value of (H) for each solute was determined in each solvent mixture over 10 different linear velocities that covered the normal practical range of velocities used in LC. Measurements at each velocity were taken in triplicate which resulted in a minimum of 180 values of (H)  being taken for each solute. Each data set, from each solvent mixture, was fitted to each dispersion equation and the values for the respective constants (A), (B), (C), etc. calculated, together with the index of determination for each fitting. It is seen that the data was sufficient in both quantity, and quality to be able to identify the most appropriate dispersion equation with some confidence. The results obtained are shown in table 2.

Examination of the results obtained by Katz et al as given in table 2 show rational fits between the experimental data and the equations of Van Deemter, Giddings and Knox. The fit of the data to both the Huber and Horvarth equations gave alternating positive and negative values for the D constant which is the coefficient of the term involving a fractional power of (u).