Indicates the reduced plate height (h) of the separation. The reduced plate height is a dimensionless measure of the performance of a HPLC column under a particular set of conditions. Here h is dimensionless because the HETP is normalized to the particle size (dp), which allows for comparisons of the performance of columns packed with different particle sizes. The reduced plate height is most commonly calculated using the van Deemter equation, which incorporates three empirically determined parameters, A, B, and C, that are characteristic of a particular type of packing material.
where
h = reduced plate height
ν = reduced flow velocity
A = reduced A parameter
B = reduced B parameter
C = reduced C parameter
The reduced velocity ν is a very important number. In physical terms, it represents the relative contributions of convection and diffusion to axial transport of the analyte through the column. So, when ν = 1, convection and diffusion contribute equally to movement of the analyte through the column. When ν << 1, axial transport is dominated by diffusion, and when ν >> 1, axial transport is dominated by convection.