GPC/SEC theory: Separation
The principle of GPC/SEC is the separation of molecules based on their hydrodynamic radius (Rh) or volume (Vh), not molecular weight. The separation process takes place in a column which is packed with porous, microparticulate material of typically 5 to 20 µm such as styrenedivinylbenzene gel, silica gel etc.
Because of their size, the larger molecules are excluded from some of the pores in the packing material and therefore elute faster through the column than the smaller molecules. In effect, the molecules are sorted by size, with the largest eluting first and the smallest last. The figure below illustrates the mechanism of GPC separation.
The GPC/SEC process starts with a continuous flow of the mobile phase through the system by means of a solvent delivery device, most commonly an isocratic pump. An in-line solvent degasser is employed to eliminate any dissolved gases in the line so that signal instability and noise are reduced. The sample is injected into the system either manually or by an autosampler.
The sample solution is then carried through the column(s) where the size separation process takes place. When the sample elutes from the column(s) it passes through a detector or series of detectors and the output is analyzed by a GPC/SEC software package on the computer.
The extent of the data analysis depends on the type and number of detectors used in the experiment. Depending on the choice of detectors, various types of calibrations and/or calculations are employed to compute parameters like molecular weight (MW), molecular weight distribution (MWD), intrinsic viscosity (IV) or molecular density, hydrodynamic radius (Rh), and radius of gyration (Rg). It is also possible to obtain additional information on macromolecular structure, conformation, aggregation, branching and copolymer/conjugate composition.
Systems for GPC/SEC:
The Viscotek TDAmax is a complete, temperature controlled, advanced, multidetector GPC/SEC system suitable for all macromolecular applications, particularly research. It consists of three unique and complementary components – The Triple or Tetra Detector Array (TDA), the GPCmax integrated solvent and sample delivery module and the OmniSEC software.
The Viscotek 270max is a modular advanced multi detector detector system that operates at ambient temperature. It is perfect for the routine full characterization of natural and synthetic polymers, copolymers and proteins.
The Viscotek RImax is a modular, conventional calibration system. It offers simple operation and full upgradeability to advanced detection. Designed for routine GPC/SEC and teaching purposes. Operates with the same powerful OmniSEC software as used in the advanced systems.