gelpermeation

Gel permeation chromatography (GPC), also known as size-exclusion chromatography (SEC), is a chromatographic technique used to characterize macromolecules in solution by their size in a swollen state. The method relies on a column packed with porous beads made of cross-linked polymers or inorganic materials. As a polymer solution passes through the column, molecules are separated primarily by hydrodynamic volume: large molecules cannot enter many pores and elute first, while smaller molecules penetrate more pores and elute later. The separation reflects effective size rather than direct molecular weight.

Calibration is required to relate elution volume to molecular weight, typically using polymer standards of known weight. Polystyrene standards are commonly employed, producing a calibration curve that converts elution volume to apparent molecular weight. Modern systems often combine multiple detectors to enrich data, including refractive index (RI) or UV for concentration, and light scattering (such as multi-angle light scattering, MALS) or viscometry for determining absolute molecular weights and intrinsic viscosity.

Outputs and concepts often reported include the number-average molecular weight (Mn), weight-average molecular weight (Mw), and the polydispersity index (PDI = Mw/Mn), which expresses the breadth of the molecular weight distribution. Applications span polymer science for quality control, process development, and research, as well as the analysis of biopolymers such as proteins and polysaccharides when appropriate columns and solvents are used.

Limitations include dependence on the calibration standard, potential interactions between analyte and the stationary phase, and the influence of molecular conformation on hydrodynamic volume. Consequently, SEC/GPC provides relative molecular weight information rather than absolute values for all polymers, and results should be interpreted with awareness of these factors.