Frans_M_Everaerts_Isotachophoresis_378342.pdf

Chapter 1
Historical review
SUMMARY
Mens ugitat molem*
1. HISTORICAL REVIEW
In the middle of the nineteenth century, Wiedeman [1,2] and Buff [3] reported on
the phenomenon that charged particles migrate in a solution when an electric field is
applied. Later experiments, carried out by Lodge [4] and Whetham [S, 61 , were the
basis on which Kohlrausch [7] developed a theory of ionic migration. With the equation
that he derived, all electrophoretic principles can be described**, including zone electro-
phoresis, moving-boundary electrophoresis and isotachophoresis.
The discovery by Hardy [8,9] that many biocolloids, such as proteins, show
characteristic mobilities that depend largely on the pH of the electrolyte solution in
which the analysis is performed, greatly stimulated interest in electrophoretic work. The
characterization of such substances on the basis of their electrophoretic properties,
especially the pl points, increased interest in electrophoretic separation techniques.
As an early example, the work of Michaelis [ 101 can be considered. He found that
enzymes can be characterized on the basis of their isoelectric points, measured in
migration experiments performed at various pH values; this work, of course, was carried
out before pure enzymes were available.
Although at first the terms cataphoresis and electrophoresis were introduced in order
to indicate the migration of charged colloidal particles and the term ionophoresis was
reserved for substances of lower molecular weight, nowadays most workers use the term
electrophoresis to describe the migration of charged particles in aqueous and non-aqueous
stabilized and free solutions.
Perhaps owing to the major interest in compounds such as proteins and enzymes, or
because high-resolution detectors had not been developed, most attention was paid to
only one of the basic principles, as already described by Kohlrausch [7] , namely zone
electrophoresis and few reports dealing with the other principles were published. It is a
fact that substances such as proteins need appropriate stabilization by electrolytes, as
discussed in Chapter 13.
It was not until about 1923 that a principle of electrophoresis other than zone
electrophoresis was described. Kendall and Crittenden [ 1 I] succeeded in separating rare
*Motto, University of Technology, Eindhoven.
** In Chapter 2, isoelectric focusing is also briefly described because it is a separation technique that
has many similarities with electrophoretic techniques, although once separated the charged particles
do not migrate if the amphiprotic compounds have reached their isoelectric points (the overall
charge is zero).
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