ABSTRACT
Axial dispersion of a solute in a column is also responsible for
the dispersion of a solute in a chromatographic column as well as
intraparticle diffusion (Chap. 4). In the usual case, the axial
dispersion in an ion-exchange chromatographic column can be
treated in a way similar to that in a gel chromatographic column
or in a column packed with nonporous packing materials. Ac-
cording to the mass balance model I given in Sec. 2. 1. 3, the
mass balance equation in a column with porous gels is given by
Eq. (5.1) (the effect of mass transfer across the mobile/gel
phase interface is ignored) with appropriate initial and boundary
conditions:
ac at
p
(5.1)
Equation (5.1) is rearranged in nondimensional form as
12H aC*1 Fe ad* d*=l
(5.2)
where t* = tU/dp C* = C/Cref (Cref is any fixed concentration) Pe = dpu/DL
z* = z/dp Pe = dpu/D
d* = d/dp = 2r/dp
The Peclet number Pe dpu/DL indicates the degree of axial
dispersion in a column. The higher the Pe number, the smaller
is the dispersion of a solute in a column. For a column with
nonporous packing materials, the third terms on the right-hand
side of Eqs. (5.1) and (5.2) are eliminated. In this case the
dispersion of a solute (second central moment 112) in a column
is expressed as
2 Peu
(5.3)
where Z = length of a column. On the other hand, \.I 2 is given
by Eq. (5.4) according to the plate theory (see Secs. 2. 1.5
and 2.1.6) (Martin and Synge, 1941).
