different chemicals have different
adsorption properties, they separate over time. One chemical,
for example, that does not stick well to the column will rush right
through and the detector produces a spike in a graph to reveal its
presence. Then, at later times other more sticky solutes will come
off the column and produce delayed peaks. The tracing of the various
peaks is called a chromatogram. If you carefully time when the peaks
occur, you can actually collect the solutes at the other end.
Gas chromatography is not
very useful for proteins. Know why? It is the heat, which denatures
and destroys proteins.