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GPC (Gel Permeation Chromatography)
GPC (Gel Permeation Chromatography) is the most useful technique for determining the molecular weight distribution of polymers. It is similar to HPLC in that it involves a stationary phase and a mobile phase. It differs from HPLC in that the separation is strictly based on the size of the molecule and is not subject to any interaction between the sample, mobile phase or the stationary phase. It is essentially a size exclusion chromatographic (SEC) technique where the separation is accomplished by moving the molecules through a porous column packing using a solvent. Through repeated exchange of the sample molecule between the solvent (eluent) and the stagnant liquid phase within the pores of the packing, the molecules are separated. The average pore size of the column packing determines the molecular size range of the sample. The weight average (Mw), number average (Mn), the Z-average (Mz) as well as the polydispersity index (PDI) are provided for each analyzed sample.
Both organic (GPC) and aqueous (GFC) SEC modes are available for analyzing polymers soluble in organic solvents or aqueous solvents respectively. Polymers in finished parts or virgin forms can be analyzed. Information about additives that absorb in the UV-Vis region of the spectrum can be provided by recording the spectrum for the appropriate peak using the PDA detector.
The HPLC/GPC system available at NDE Analytical is Waters quaternary pump, an autosampler, index of refraction (RI), photodiode array (PDA), and evaporative light scattering (ELS) detectors. The software is the Waters Empower software with the GPC option.