Dispersion in Chromatography Columns - Experimental Validation of the Van Deemter Equation > Page 83

Although a good fit is obtained to the Giddings equation, the value of (E) is shown to be numerically equal to zero. This is further evidence that the Van Deemter equation can be considered to be a special case of the Giddings equation, where, at the linear velocities employed (i.e. those normally employed in practical LC), the constant (E) was zero or tended to zero. It is quite probable, however, that if mobile phase velocities are considered outside the range studied, the Giddings equation would be more appropriate. There does not appear to be  sufficiently precise data available at this time to test this possibility. In any event, the Van Deemter equation and the Knox equation are the two that must be further considered as they do describe the experimental data accurately.

The Van Deemter equation in explicit form is,

 

(61)

                     

 and that of Knox,

                (62)

where,   (g) and (g') are constants  

    and    the other symbols the meanings previously ascribed to them.