Extracting Information
from the Ionic Strength Dependence
of Electrophoretic Mobility by Use of the Slope Plot
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Abstract
The effective mobility (μ<sub>ep</sub>) is the
main parameter
characterizing the electrophoretic behavior of a given solute. It
is well-known that μ<sub>ep</sub> is a decreasing function of
the ionic strength for all solutes. Nevertheless, the decrease depends
strongly on the nature of the solute (small ions, polyelectrolyte,
nanoparticles). Different electrophoretic models from the literature
can describe this ionic strength dependence. However, the complexity
of the ionic strength dependence with the solute characteristics and
the variety of analytical expressions of the different existing models
make the phenomenological ionic strength dependence difficult to comprehend.
In this work, the ionic strength dependence of the effective mobility
was systematically investigated on a set of different solutes [small
mono- and multicharged ions, polyelectrolytes, and organic/inorganic
(nano)particles]. The phenomenological decrease of electrophoretic
mobility with ionic strength was experimentally described by calculating
the relative electrophoretic mobility decrease per ionic strength
decade (<i>S</i>) in the range of 0.005–0.1 M ionic
strength. Interestingly, the “slope plot” displaying <i>S</i> as a function of the solute electrophoretic mobility at
5 mM ionic strength allows for defining different zones that are characteristic
of the solute nature. This new representative approach should greatly
help experimentalists to better understand the ionic strength dependence
of analyte and may contribute to the characterization of unknown analytes
via their ionic strength dependence of electrophoretic mobility