Gel permeation chromatography GPC , also known as size exclusion chromatography SEC , is a widely used technique to determine the molecular weight distribution of a polymer sample. The method separates polymer chains based on their size in solution, allowing for the determination of molecular weight averages and dispersity. Here's a step-by-step guide on how to use GPC for this purpose:1. Preparation of the sample: Dissolve the polymer sample in an appropriate solvent to create a homogeneous solution. The concentration should be within the recommended range for the GPC system being used, typically around 1-5 mg/mL.2. Selection of columns and mobile phase: Choose a suitable GPC column or a series of columns with an appropriate pore size and particle size that can effectively separate the polymer chains based on their size. The mobile phase should be a solvent that is compatible with both the polymer and the column packing material.3. Calibration of the GPC system: Run a series of polymer standards with known molecular weights through the GPC system to generate a calibration curve. These standards should cover the molecular weight range of interest for the sample being analyzed. The retention times of the standards are plotted against their molecular weights or hydrodynamic volume to create the calibration curve.4. Sample injection and analysis: Inject the prepared polymer sample into the GPC system and allow it to pass through the column s under a constant flow of the mobile phase. The polymer chains will be separated based on their size, with larger chains eluting first and smaller chains eluting later.5. Detection and data collection: As the separated polymer chains elute from the column, they will pass through a detector, typically a refractive index RI or ultraviolet UV detector. The detector will generate a signal proportional to the concentration of the polymer chains at each elution time. This signal is recorded and plotted as a chromatogram, showing the intensity of the signal as a function of elution time or elution volume.6. Data analysis: Using the calibration curve generated in step 3, convert the retention times or elution volumes of the sample peaks to molecular weights. This will provide the molecular weight distribution of the polymer sample. From this distribution, various molecular weight averages e.g., number-average molecular weight Mn , weight-average molecular weight Mw , and z-average molecular weight Mz and dispersity or polydispersity index PDI , calculated as Mw/Mn can be calculated.By following these steps, gel permeation chromatography can be effectively used to determine the molecular weight distribution of a polymer sample, providing valuable information about the sample's properties and potential applications.