Gel permeation chromatography (GPC) is a type of size exclusion chromatography (SEC), that separates analytes on the basis of size, typically in organic solvents. The technique is often used for the analysis of polymers. As a technique, SEC was first developed in 1955 by Lathe and Ruthven. The term gel permeation chromatography can be traced back to J.C. Moore of the Dow Chemical Company who investigated the technique in 1964 and the proprietary column technology was licensed to Waters Corporation, who subsequently commercialized this technology in 1964. GPC systems and consumables are now also available from a number of manufacturers. It is often necessary to separate polymers, both to analyze them as well as to purify the desired product.

When characterizing polymers, it is important to consider the dispersity (Đ) as well the molecular weight. Polymers can be characterized by a variety of definitions for molecular weight including the number average molecular weight (Mn), the weight average molecular weight (Mw) (see molar mass distribution), the size average molecular weight (Mz), or the viscosity molecular weight (Mv). GPC allows for the determination of Đ as well as Mv and based on other data, the Mn, Mw, and Mz can be determined.

GPC is a popular method for determining the molecular-weight distribution of a polymer. The preference for GPC is because of its relatively low cost, simplicity, and ability to provide accurate, reliable information about the molecular-weight distribution of a polymer. GPC is based on separation by molecular size rather than chemical properties. It employs the principle of size-exclusion chromatography (often referred to as SEC) to separate samples of polydisperse polymers into fractions of narrower-molecular-weight distribution. The details of the analytical procedure are given in several publications. For quality control, a master chromatogram representing acceptable range of GPC profiles is kept in the data file and subsequent samples are compared with this standard. Some internal correlations can be established with respect to batch-to-batch uniformity and some information about the processability and mechanical properties of the polyolefin.

1. Gel permeation chromatography is also called as gel filtration or size exclusion chromatography.
2. In size exclusion chromatography, the stationary phase is a porous matrix made up of compounds like cross-linked polystyrene, cross-like dextrans, polyacrylamide gels, agarose gels, etc.
3. The separation is based on the analyte molecular sizes since the gel behaves like a molecular sieve.
4. This technique is used for the separation of proteins, polysaccharides, enzymes, and synthetic polymers.
5. As a technique, size exclusion chromatography was first developed in 1955 by Lathe and Ruthven.

To perform gel permeation chromatography, a solvent is first used to dissolve the sample of interest. The fluid is then continuously pumped into an adsorbent bed, typically comprised of porous gel beads packed into a column. Smaller sample molecules spend more time passing through the porous structure of the column and will take longer to pass through the stationary phase. Conversely, a larger sample molecule cannot traverse through comparatively small pores and will pass through the column quickly. This property is reflective of the individual molecules’ hydrodynamic volumes.The eluted mobile phase molecules can be detected using any of the following techniques:

• Evaporative light scattering (ELSD)
• Fourier Transform Infrared Spectroscopy (FTIR)
• Low Angle Light Scattering (LALS)
• Refractive Index (RI)
• Right Angle Light Scattering (RALS)
• Ultraviolet (UV)
• Viscometry

It is possible to analyze an extremely wide range of molecular weights using gel permeation chromatography columns due to the development of a broad range of specially designed porous polymer packings. Conventional chromatography packings are unsuitable for detecting large molecules as they are often retained in the solid porous structure and do not elute from the column.

Regards,

Hanna Marin,

Managing editor,

Journal of Analytical and Bioanalytical Techniques

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