Aqueous GPC/SEC

Aqueous Gel Permeation Chromatography/Size Exclusion Chromatography

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  • How big is my polymer? 
  • Has crosslinking or chain scissioning occurred?
  • Has my reaction worked?
  • Why has my solution viscosity dropped?
  • Is my material degrading?
  • Do I have unreacted products?
  • How pure is my sample?

Cambridge Polymer Group investigates the above questions for water-soluble polymers using Gel Permeation Chromatography (GPC), sometimes referred to as Size Exclusion Chromatography (SEC).

Gel permeation chromatography (GPC) is a form of liquid chromatography which separates compounds on the basis of size or hydrodynamic volume. This is performed by passing a sample (consisting of a mixture of molecular weights) through a column typically packed with porous micro-spheres. These spheres make up the stationary phase of the column and often possess a range of pore sizes.

Smaller analytes are able to pass into smaller stationary phase pores and therefore experience a longer “path length” through the column than larger analytes.

This separation mechanism is distinct from the most commonly performed HPLC separations which depend on relative affinity (chemical or physical interactions) between the compound and a stationary phase. 

GPC Outputs

The outputs of the GPC analysis include the following:

  1. Number average molecular weight or Mn
  2. Weight average molar mass or Mw
  3. Z average molar mass or Mz
  4. Peak molecular weight or Mp
  5. Polydispersity index (PDI), or Mw/Mn
  6. Molecular weight distribution

Samples to be analyzed are tested alongside reference standards of certified molecular weight moments. The resulting data is processed to generate a calibration curve for the column relating the logarithm of molecular weight to the retention time during the run.

Tested samples are mapped onto this calibration curve to determine their molecular weight distribution and for calculation of molecular weight moments and polydispersity index.  The general method described here is not dependent on the choice of column, mobile phase, or detector.

GPC/SEC Applications

Multi-Detector GPC

As compounds elute a signal is generated by an appropriate detector. For compounds with chromophores a diode array detector (DAD) may be used to measure UV-VIS absorption at a characteristic absorption band. For compounds that are ionizable a mass spectrometer may be used to measure the total ion intensity. Most compounds may be detected by an evaporative light scattering detector (ELSD), a non-specific detector for semi-volatile and non-volatile analytes. Another common detector used for GPC analysis is the refractive index (RI) detector. 

Example Materials

  • Polyacrylic Acid
  • Polyvinylpyrrolidone
  • Polyvinyl Alcohol
  • Dextran
  • Polymethylacrylic Acid
  • Poly(allylamine) Hydrochloride
  • Hydroxypropyl Cellulose
  • Hydroxyethyl Starch
  • Polyacrylamide
  • Chitosan
  • Hydroxypropyl Methylcellulose
  • Hydroxyethyl Cellulose
  • Polyethylene Glycol
  • Xanthan
  • Carboxymethyl Cellulose
  • Pullulan
  • Polyethylene Oxide
  • Guar Gum
  • Poly (2-Vinylpyridine)
  • Proteins
  • Polystyrene Sulfonate