Gel Permeation Chromatography is a column fractionation method based on the molecular sieve effect. It is a form of liquid chromatography in which the solute molecules are separated as a result of their permeation into a solvent filled matrix in the column packing. The particles of the column packing have various size pores and pore network, so that the solute molecules are retained or excluded on the basis of their hydrodynamic volumes, that is their size and shape. In so doing the stationary phase can effect a separation according to molecular weight.