Borek, hes talking about gel permeation chromatography, also called size exclusion chromatography. It depends on the mean free path length of molecules in solution through a porous column as a function of hydrodynamic volume. The larger the molecule the shorter its path because it can't pass through some fraction of the pores which are under a certain size. High MW polymers elute before low MW polymers and small molecules come off last. Its how polymer molecular weight is usually determined.
permanganate, I've never heard of GPC being used for determining concentration. For one thing, GPCs work a few different ways. They can be UV detectors, light scattering detectors, or viscometers. UV detectors have a pretty linear response to concentration, but light scattering and viscocity are probably different ball games. These detectors are also very very sensitive, and I bet your injection volume will vary a little, so you would need a standard of some kind in there that is very separated from the other peaks. In all detector cases more polymer=more signal but deconvoluting it is what I would consider "very very tricky at best."