Van Deemter equation

The van Deemter equation in chromatography, named for Jan van Deemter, relates the variance per unit length of a separation column to the linear mobile phase velocity by considering physical, kinetic, and thermodynamic properties of a separation.

[1] These properties include pathways within the column, diffusion (axial and longitudinal), and mass transfer kinetics between stationary and mobile phases.

Alternatively, the linear velocity can be taken as the ratio of the column length to the dead time.

The van Deemter equation is a hyperbolic function that predicts that there is an optimum velocity at which there will be the minimum variance per unit column length and, thence, a maximum efficiency.

The van Deemter equation was the result of the first application of rate theory to the chromatography elution process.

The van Deemter equation relates height equivalent to a theoretical plate (HETP) of a chromatographic column to the various flow and kinetic parameters which cause peak broadening, as follows: Where In open tubular capillaries, the A term will be zero as the lack of packing means channeling does not occur.

The form of the Van Deemter equation is such that HETP achieves a minimum value at a particular flow velocity.

At this flow rate, the resolving power of the column is maximized, although in practice, the elution time is likely to be impractical.