Band broadening Knox equation

The van Deemter equation is a useful approximation however, the experimental H u plots often show some downward curvature on the right-hand branch, unpredicted by Eq. (1.10). Giddings explained this behaviour by coupling the flow and the diffusion effects which demonstrates that it is not strictly correct to consider the simple additivity of their contributions to band broadening and he suggested more sophisticated equations to account for this phenomenon [3. For practical purpose, a simple empirical equation, which accounts for the experimental behaviour and is only slightly different from the van Deemter expression was introduced by Kennedy and Knox [4. ... 

Relationships between mobile phase velocity and column efficiency, such as the Knox equation (equation (2.32)), are developed by taking into account all the possible contributions to band broadening. Thus the total peak variance (a oiumn) arising from band broadening in a packed column is given by... 

Defining separation in terms of the selectivity factor (equations (2.41)-(2.43)) ignores the effects of peak width and band broadening. The resolution factor (Rs) is defined by equation (2.44), which takes into account both the difference in retention as well as the average peak widths of the two peaks (0.5(wb,i + Wa,i)) (Knox, 1977). 

B term The component of the van Deemter and Knox equations that describes the impact that longitudinal diffusion has on the band broadening process. 

Eddy diffusion Also called axial diffusion, a band-broadening effect caused by the flow stream splitting around particles in the packed bed of a colrunn. It is a component of the A term in the van Deemter and Knox equations. 

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