Equations • 7 Theoretical plates


N, the number of theoretical plates, is one index used to determine the performance and effectiveness of columns, and is calculated using equation


where tr = retention time W = peak width at base


N = `j16 tr 2 W


• 8 Van Deemter equation


The van Deemter equation relates the theoretical plate height, or efficiency, of a chromatographic column to the various flow and kinetic parameters which cause peak broadening, as follows:


HETP A B Cu = ++ $ u


Where HETP = height equivalent to a theoretical plate, a measure of the resolving power of the column [m] A = Eddy-diffusion parameter, related to channeling through a non-ideal packing [m] B = diffusion coefficient of the eluting particles in the longitudinal direc- tion, resulting in dispersion [m2 s-1] C = Resistance to mass transfer coefficient of the analyte between mobile and stationary phase [s] u = Linear Velocity [m s-1


]


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