Gel Permeation Chromatography GPC

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Gel Permeation Chromatography (GPC)
Kelechi C. Anyaogu
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Concept GPC is a high performance liquid
chromatography technique for the separation of
components based on their molecular size in
solution. It is a method widely used today for
determining the molecular size and molecular
weight distribution of high polymers. It is also
known as size exclusion chromatography (SEC) or
gel filtration chromatography (GFC).

• Principle
• GPC provides a physical means for separating
  molecules by their size in solution
• hence widely used in the analysis of polymer
  weights or molar mass.
• There is a distribution of pore sizes within
  the packing (stationary phase) such that
• the small molecules can enter most of the pores
  and are therefore retained the
• the longest, while the larger molecules enter
  fewer pores and are retained a shorter
• time period.

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• GPC Instrumentation
• Pumps - for maintaining constant rates of flow.
• Column
• Detector for quantifying the result.
• Degasser

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• In GPC , a column (steel cylinder typically 10
  mm in diameter and 500 to 1000 mm
• in length) is packed with a porous material
  (typically silica or cross-linked polystyrene)
• and solvent is forced through the column (at
  rates typically 1 ml/min and pressures of
• 50 to 200 bar).
• Mobile Phase solvent plus
  portion of the polymer
• Stationary phase the porous
  material ( eg. polystyrene)

• A sample is dissolved in the same solvent that
  is running through the column and
• is then introduced into the solvent stream going
  through the column.
• A detector monitors the concentration of sample
  exiting the end of the column.
• Detector systems are classified as either
  concentration sensitive or molar mass
• sensitive. The refractive index detector measures
  the change in refractive index as
• the concentration of polymer in the solution
  changes, and is usually operated on some
• type of differential refractive index method.
• Another group of concentration methods involves
  the input of ultraviolet light, with the
• output being fluorescence or absorption by the
  polymer.

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• GPC can be used to analyze soluble compounds and
  mixtures that fall in the size range
• 10 to 500 Angstroms (covers wide range of polymer
  weights).
• Requirements
• The sample may be either a solid or liquid.
• The sample must be soluble in chosen solvent.
  Commonly used organic solvents
• include toluene, tetrahydrofuran,
  trichlorobenzene, and chloroform.
• The instrument can be operated up to 140o C to
  increase solubility and reduce
• viscosity. The column oven helps to maintain
  steady temperature.
• There should not be fluctuations in pump
  pressure.
• The system is calibrated by using a polymer of
  known molecular weight. The
• calibration of the system is a plot of the
  log of the molecular weight vs. retention time.