Steric chromatography of exclusion
One calls steric chromatography of exclusion ( SEC ) a method of Chromatography in liquid phase allowing to determine the average molar masses Polymère S.
Principle
Contrary to the methods of conventional Chromatography, the physical phenomenon allowing the separation of different the Macromolécule S constituting polymer is not based on chemical affinity with the support, but simply on the size of the macromolecules (their hydrodynamic volume). Indeed, according to their size, the éluées molecules can or not penetrate in the porous balls of which the columns are filled. Thus, the smallest molecules are retained whereas largest éluent more quickly. At exit of column, detectors (viscometer, photometer,…) we provide the number of macromolecules leaving the column to a given moment.
Calibration and its importance
To obtain values of the average molar masses of polymers, it is necessary to have one or more calibration curves indicating the average molar mass according to the hydrodynamic volume of the macromolecules. It will be noted that this hydrodynamic volume can be different for two of the same mass macromolecules molar but of different architecture. A nonlinear macromolecule (ex: out of comb) a greater volume than a macromolecule molar of the same mass occupywill occupy linear and will thus be éluée more quickly even if the two molar masses are identical! Ce that one must retain: one needs various calibration curves for each polymer and also for each type of architecture of same polymer.
There exists also a universal method of calibration making it possible to determine the average molar polymer masses of architecture or different chemical composition. Such a calibration however requires a material more sophisticated and is slightly more difficult to realize than a conventional calibration.
Synonyms
This method is also called gel chromatography permeable and is often shortened in GPC according to English Gel Permeation Chromatography .Another synonym: freezing filtration chromatography
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