GPC/SEC
Gel Permeation Chromatography Size Exclusion Chromatography · Also known as: size exclusion chromatography, molecular weight determination, polymer characterization
Gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), is an analytical technique for determining the molecular weight distribution (MWD) and average molecular weight (Mw, Mn) of polymers. The method separates polymer molecules by their hydrodynamic size as they pass through a porous chromatography column: larger molecules elute first (excluded from pores), while smaller molecules are retained longer. Developed by Moore and colleagues in the 1960s, GPC/SEC is now the standard method for characterizing polymer chains, assessing polymer degradation over time, and verifying batch consistency in biomaterial production.
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When to use it
GPC/SEC is essential for characterizing newly synthesized polymers, assessing polymer batch-to-batch consistency in manufacturing, monitoring polymer degradation kinetics (e.g., PLGA, PLA hydrolysis), and evaluating whether polymer chain-breaking events are occurring as designed. It is the method of choice for polymers with molecular weights from ~1,000 to ~10 million Da. However, GPC/SEC provides hydrodynamic size distribution (how molecules behave in solution), not absolute molecular weight unless coupled with light scattering. For very small oligomers (<1000 Da) or very large proteins (>1 MDa), alternative methods may be more suitable.
Strengths & limitations
- Quantitative MWD: provides complete distribution of molecular weights, not just averages.
- Fast and automated: modern GPC systems run autonomously, analyzing multiple samples per day.
- Reproducible calibration: standard polymers enable reliable conversion of elution time to molecular weight.
- Sensitive to degradation: even small changes in average molecular weight (e.g., 5%) are detectable, enabling sensitive monitoring of degradation.
- Works with diverse solvents: GPC systems can accommodate aqueous and organic solvents, enabling analysis of most synthetic and natural polymers.
- Hydrodynamic size versus absolute size: GPC measures elution size, not true molecular weight, unless coupled with light scattering or other absolute methods.
- Polymer-column interactions: some polymers interact with column material, causing peak broadening or anomalous elution; use appropriate column chemistries.
- Solvent effects: choice of solvent affects polymer conformation and thus apparent size; use consistent solvents for inter-sample comparison.
- Limited to dissolved polymers: GPC cannot analyze polymers that do not dissolve readily; cross-linked polymers and insoluble aggregates are invisible.
Frequently asked
What is the difference between Mw and Mn?
Mn (number average) weights each molecule equally; Mw (weight average) weights larger molecules more heavily (by mass). For monodisperse polymers, Mw = Mn. For polydisperse polymers, Mw > Mn; the ratio Mw/Mn (polydispersity index) indicates breadth of distribution.
Do I need light scattering detection, or is a refractive index detector sufficient?
RI detection provides relative molecular weight (based on calibration). Light scattering (MALS or LALLS) provides absolute Mw without standards. For most applications, RI detection suffices; MALS is valuable for polymers that don't match calibration standards well or for absolute accuracy requirements.
How do I choose the right solvent for my polymer?
Solvent should fully dissolve the polymer without degrading it. Common choices: THF for most synthetic polymers, DMSO for PEG and water-soluble polymers, chloroform for PS and some polyesters. Consult literature or test small amounts to verify dissolution.
Why is my peak so broad, and what does it mean?
Broad peaks indicate polydisperse polymer (wide MWD), which is normal for most synthetic polymers. Very broad peaks may suggest aggregation, incomplete dissolution, or column overloading; try injecting less material or checking sample preparation.
Can I use GPC to measure protein molecular weight?
Yes, aqueous GPC (using PBS or similar as solvent) can measure protein Mw. However, proteins may adsorb to columns, causing peak distortion. Use protein-specific columns (gel filtration resins) and minimize column residence time.
Sources
- Striegel, A. M., Yau, W. W., Kirkland, J. J., & Bly, D. D. (2009). Modern size-exclusion liquid chromatography: practice and theory. John Wiley & Sons. link ↗
- Podzimek, S. (2011). Light scattering, size exclusion chromatography and asymmetric flow field flow fractionation: promising tools for the characterization of polymers and nanoparticles. John Wiley & Sons. link ↗
- Bateman, L. C., & Moore, C. G. (2017). Determination of molecular weight and molecular weight distribution. In The Chemistry and Physics of Rubber-Like Substances. Academic Press. link ↗
How to cite this page
ScholarGate. (2026, June 3). Gel Permeation Chromatography Size Exclusion Chromatography. ScholarGate. https://scholargate.app/en/biomaterials/gpc-sec
Which method?
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