  In a previous paper (S. Ghosal and Z. Chen Bull. Math. Biol. 2010, vol. 72,
pg. 2047) it was shown that the evolution of the solute concentration in
capillary electrophoresis is described by a nonlinear wave equation that
reduced to Burger's equation if the nonlinearity was weak. It was assumed that
only strong electrolytes (fully dissociated) were present. In the present paper
it is shown that the same governing equation also describes the situation where
the electrolytic buffer consists of a single weak acid (or base). A simple
approximate formula is derived for the dimensionless peak variance which is
shown to agree well with published experimental data.
