Size-exclusion chromatography separation mechanism

By contrast with other chromatographic methods, GPC (gel permeation chromatography) or SEC (size exclusion chromatography) separates according to the size of the specimen molecule in solution. This is a simple way of utilizing the exclusion principle. This very specific separation mechanism enables the determination of molecular weight distribution and dispersion index. 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

The two techniques differ in that HDC employs a nonporous stationary phase. Separation is affected as a result of particles of different size sampling different velocities in the interstitial spaces. Size exclusion chromatography is accomplished by superimposing a steric selection mechanism which results from the use of a porous bed. The pore sizes may vary over a wide range and the separation occurs as a result of essentially the same processes present in the gel permeation chromatography of macromolecules. 

The data prove that the retention order of anthocyanins deviates from each other in HPLC and TLC suggesting the involvement of a different retention mechanism. It was stated that the preseparation of anthocyanins by size-exclusion chromatography is a prerequisite of the successful preparative separation by RP-HPLC [244],... 

There are four different mechanisms of separation utilized in HPLC adsorption, partition, ion-exchange, and size exclusion chromatography. 

Gel filtration chromatography. A mode of LC in which molecules are separated according to their size using an aqueous mobile phase. Gel filtration chromatography most often is used to separate proteins and peptides. See Gel permeation chromatography for a discussion of the mechanism. Gel filtration and gel permeation chromatography are sometimes referred to as size exclusion chromatography (SEC). 

Size exclusion chromatography is the premier polymer characterization method for determining molar mass distributions. In SEC, the separation mechanism is based on molecular hydrodynamic volume. For homopolymers, condensation polymers and strictly alternating copolymers, there is a correspondence between elution volume and molar mass. Thus, chemically similar polymer standards of known molar mass can be used for calibration. However, for SEC of random and block copolymers and branched polymers, no simple correspondence exists between elution volume and molar mass because of the possible compositional heterogeneity of these materials. As a result, molar mass calibration with polymer standards can introduce a considerable amount of error. To address this problem, selective detection techniques have to be combined with SEC separation. 

Ion exchange chromatography uses an ion exchange resin as the stationary phase. The mechanism of separation is based on ion exchange equilibria. In size exclusion chromatography, solvated molecules are separated according to their size by their ability to penetrate a sievehke structure (the stationary phase). 

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