(B) Gel filtration chromatography # Gel filtration chromatography:> Separation of molecules is based on their size, shape and molecular weight.> Technique is also referred to as molecular sieve or molecular exclusion chromatography.> Apparatus consists of a column packed with sponge like gel beads (usually cross-linked polysaccharides) containing pores.> Gels serve as molecular sieves for the separation of smaller and bigger molecules.> Gel-filtration chromatography can be used for an approximate determination of molecular weights.> This is done by using a calibrated column with substances of known molecular weight.> Partition chromatography: Molecules of a mixture get partitioned between the stationary phase and mobile phase dependir g on their relative affinity to each one of the phases.> Ion-exchange chromatography: Ion-exchange chromatography involves the separation of molecules on the basis of their electrical charges Ion-exchange resins--cation exchangers and anion exchangers--are used for this purpose.> Affinity chromatography: The principle of affinity chromatography is based on the property of specific and non-covalent birding of proteins to other molecules, referred to as ligands.> For instance, enzymes bind specifically to ligands such as substrates or cofactors.