# Dispersion in Chromatography Columns - The Van Deemter Equation > Page 56

_{}

Bearing in mind the values of (l) and (g) for a well packed column are 0.5 and 0.6 respectively,

H_{min.} =
1.48d_{p }

Thus, the
approximate value of H_{min,} for
a well retained solute eluted from a well packed column and operated at the
optimum linear mobile phase velocity, can be expected to be about 1.48d_{p. }Furthermore, to the first approximation,
this value will be independent of the nature of the solute, mobile phase or
stationary phase. For the accurate design of the optimum columns for a
particular separation, however, this approximation should, in general, not be
made, nevertheless, the value of 1.48 for H_{min}
is a useful guide for assessing the quality of a column. From d'Arcy's Law for
fluid flow through a packed bed, at the optimum mobile phase velocity the
length of the column is given by,

where (P) is the inlet pressure to the column,

(h) is the viscosity of the mobile phase,

(j) is the d'Arcy's Constant.