Capillary electrophoresis measurements of the free solution mobility
for several model polyelectrolyte systems
Macromolecules, 32 (19):
6180--6190 (September 1999)Abstract
The free solution electrophoretic mobilities of poly(styrenesulfonate),
ss-DNA, and duplex DNA are measured by capillary electrophoresis
across a range of ionic strengths and, for poly(styrenesulfonate)
and ss-DNA, across a range of chain lengths. The data are then compared
with mobilities reported in the literature and predicted by theory.
For ionic strengths below 0.1 M, the capillary method is more accurate
and rapid than previous techniques; it also provides a distribution
of mobility values for polyelectrolyte mixtures. A maximum of the
free solution mobility with respect to chain length is discovered
in the oligomer range for both poly(styrenesulfonate) and ss-DNA;
lowering ionic strength accentuates this unexplained phenomenon.
In the large chain limit, where the mobility is independent of chain
length, the ionic strength dependences of mobility for all three
polymers are remarkably similar. These dependences can only be explained
by models that incorporate nonlinear electrostatic effects into the
description of the counterion cloud. The Manning model (with relaxation
correction) best approximates the dependence of mobility on ionic
strength.