Q: What is the difference between GPC, GFC, SEC and HPLC? A: Size exclusion chromatography (SEC) is a chromatographic method in which particles are separated based on their size, or in more technical terms, their hydrodynamic volume. It is usually applied to large molecules or macromolecular complexes such as proteins and industrial polymers. Both molecular weight and three dimensional shape contribute to the degree of retention. (view the principle  as  portrayed by General Electric Corporation) When an aqueous solution is used to transport the sample through the column the technique is known as gel filtration chromatography. The name gel permeation chromatography is used when an organic solvent is used as a mobile phase.  GPC must operate free of interactions to assure separation by size only. Only the entropy effects should influence the separation.  Normal HPLC methods rely on interactions between sample and stationary phase;those interactions result from ion exchange, bio-affinity, or chirality. Gel Permeation Chromatography (GPC) is one of the most versatile and powerful analytical techniques available for understanding and predicting polymer performance.  GPC is well established for determining the molar mass of polymers.  Compared to other methods of analysis such as osmometry or static light scattering, it has the advantage that it determines complete distributions of molar masses as opposed to merely an average molecular weight.  GPC separates the molecules in solution by their "effective size" or Hydrodynamic volume.  The sample is dissolved in an appropriate solvent and injected into a continually flowing stream of solvent (mobile phase).  The mobile phase flows through millions of highly porous, rigid particles (stationary phase) tightly packed together into a column. As the mobile phase flows through the column the smaller molecules penetrate more pores than the larger molecules. As a result, the smaller molecules take longer to emerge from the column than the larger molecules The width of the individual peaks reflects the distribution of the size of molecules for a given polymer (macromolecule) and its components. High Performance Liquid Chromatography (HPLC) is an analytical technique for the separation and determination of organic and inorganic solutes in any samples especially biological, pharmaceutical, food, environmental, industrial, etc. In a liquid chromatographic process a liquid permeates through a porous solid stationary phase and elutes the solutes into a flow-through detector. The stationary phase is usually in the form of small-diameter (5-10 mm) uniform particles, packed into a cylindrical column. The typical column is constructed from a rigid material (such as stainless steel or plastic) and is generally 5-30 cm long and the internal diameter is in the range of 1-9 mm.