The right flow rate is dependent on column dimension. The ’’Van-Deemter equation’’ shows the correlation between column length and flow rate:
H= A+(B/v)+C⋅v
The smaller the H value, the better the separation effieciency of the system: H=L/N H or HETP: height equivalent to a theoretical plate
L: column length
N: number of theoretical plates
v: linear velocity of mobile phase
A: Eddy-diffusion parameter, related to channeling through a non-ideal packing
B: diffusion coefficient of the eluting particles in the longitudinal direction,
resulting in dispersion
C: Resistance to mass transfer coefficient of the analyte between mobile and
stationary phase
The H/v-hyperbolic function (X = v, Y = HETP) has a minimum at the optimal velocity (v),where the height equivalent to a theoretical plate (H) has the smallest value and so the separation efficiency is maximum. The following flow rates are typical guiding values for a 5 µm particle size material: ID 2mm flow 0.15ml/min-0.5ml/min ID 3mm flow 0.6 ml/min, ID 4 and 4.6 mm flow 0.8 ml/min-2.0 ml/min, ID 8 mm 2.0 ml/min – 4.0 ml/min.
