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Theory Answers
How does separation work in Gel Permeation Chromatography?
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GPC Theory: Separation |
Separation
The principle of GPC operation is the separation of molecules based on their hydrodynamic
radius (Rh) or volume (Vh), not molecular weight. The separation process takes place
in GPC columns which are packed with porous material such as polystyrene gels, glass
beads, silica gel etc.
Because of their size, the larger molecules cannot fit into as many pores and elute
faster through the porous packing materials than the smaller molecules. The figure
below illustrates the mechanism of GPC separation.
The gel permeation chromatography process starts with 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 vapor or
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 GPC 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
data processing
system (computer).
The extent of the GPC 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 composition
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