Size Exclusion Chromatography (also known as gel filtration) separates molecules based on molecular size. This chromatography can be applied using resins or membrane. With membranes, the smaller molecules pass through while the larger molecules (above a certain size cut-off) are held above the membrane. With resins, the larger molecules pass/flow through the resin and are collected first while the smaller molecules take longer to flow through because these smaller particles get held up within the pores of the resins. Therefore, with resins, the sample passes through the resin in decreasing molecular weight. Common size exclusion applications include concentration, fractionation, desalting and buffer exchange.
Size exclusion is one of the easiest chromatography methods to perform because samples are processed using an isocratic elution. In its analytical form, size exclusion can distinguish between molecules (e.g. proteins) with a molecular weight difference of less than a factor of two times. In this application, the porosity of the filtration media to be used is selected to provide high resolution in the molecular weight range of interest.