broadly, to separate or be separated into various components or portions (fractions);
e.g. There are many ways to fractionate a mixture to separate the various substances in it.
(verb)
to separate the components of a mixture by the process of fractional distillation, which takes advantage of the different boiling points of the components;
e.g. When you fractionate the contents of the beaker, the alcohol will evaporate off, leaving the required product behind.