Powerful electrophoretic techniques have been developed to separate macromolecules
on the basis of molecular weight. The mobility of a molecule in an electric field is
inversely proportional to molecular friction which is the result of its molecular size and
shape, and directly proportional to the voltage and the charge of the molecule. Proteins
could be resolved electrophoretically in a semi-solid matrix strictly on the basis of
molecular weight if, at a set voltage, a way could be found to charge these molecules to
the same degree and to the same sign. Under these conditions, the mobility of the
molecules would be simply inversely proportional to their size.