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Gel-permeation-chromatography/Size exclusion chromatography (GPC)

Method description

Gel permeation chromatography (GPC/SEC) is the name for a liquid chromatography accomplished as column chromatography. The stationary phase consists of a porous poured network (polyacrylamide or polystyrene e.g. interlaced), whose distribution of sizes of pores varies over several orders of magnitude. The separation takes place with respect to molecule size (molecular sieve effect). A solution of the polymer which can be examined is injected to the gel, whereby smaller molecules can penetrate the entire volume of the mobile phase into all pores and leave them from there after a longer time because of the longer way the particle takes through the pores. Because the smaller the particle the more pores it can enter, the smaller particles are held back longer in the column than the larger molecules. The gel permeation chromatography is a relative method for the determination of the mol mass distribution of polymers, since the size of a molecule is generally dependent on the mol mass. In contrast to the HPLC the target molecules must be always completely solved in the mobile phase in the GPC/SEC, so that ideally no interaction effect between material which can be separated and the stationary phase takes place.

Conditions of GPC/SEC

With the GPC/SEC practically the hydrodynamic volume (volume of the molecule in solution) is determined. For mol mass regulation from there a calibration must take place. The calibration standards should behave in addition in solution similarly as the target molecule. For calibration several differently large polymer standards with low polydispersitivities are usually used. From the indicated molecule masses of the standards and the retention time received after analysis one can provide the calibration curve. With the help of the calibration curve now the molecule masses of unknown samples can be determined. As result one receives relative mol masses, related to the standard substance. Since for not each polymer narrow-distributed standard are available, the mol mass computation can be problematic on use of different standards. Although one in such cases if possible "similar" standards used, the mol mass computation can deviate dramatically from the material of interest.

Instrumentation

The GPC is accomplished by a partner of the ZEA-3. There several GPC devices are available. Beside purely organic solvents also devices with aqueous separation phase are available. Detection can take place as required with UV-VIS, refractive index or light scattering detection.

Analysis Examples

  • Molecular mass/Size distribution of synthetic polymers
  • Molecular mass distribution of bioploymers (e.g. polysaccachrides)
  • Protein fractionation by size

Contact

Herr Dr. S. Küppers Tel.: 02461-61 2766


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