Gel Permeation Chromatography GPC , also known as Size Exclusion Chromatography SEC , is a widely used technique for determining the molecular weight of polymers. The method separates polymer chains based on their hydrodynamic volume or size in solution. Here's a step-by-step guide on how to determine the molecular weight of a polymer using GPC:1. Preparation of samples and standards: Dissolve the polymer sample in a suitable solvent to obtain a concentration typically in the range of 1-10 mg/mL. Prepare a series of polymer standards with known molecular weights and similar chemical structure to the sample. Dissolve these standards in the same solvent as the sample.2. Column selection: Choose a GPC column or a set of columns with an appropriate pore size and particle size that can effectively separate the polymer chains based on their size. The column should be compatible with the solvent used for the sample and standards.3. System calibration: Inject the polymer standards into the GPC system and record their elution profiles. Measure the retention time or elution volume for each standard. Plot a calibration curve by plotting the logarithm of the molecular weight of the standards against their retention times or elution volumes .4. Sample analysis: Inject the polymer sample into the GPC system and record its elution profile. Measure the retention time or elution volume for the sample.5. Molecular weight determination: Use the calibration curve obtained in step 3 to determine the molecular weight of the polymer sample. Locate the retention time or elution volume of the sample on the x-axis of the calibration curve, and read the corresponding molecular weight on the y-axis.6. Data analysis: GPC can provide additional information about the polymer sample, such as the molecular weight distribution MWD and polydispersity index PDI . The MWD can be obtained by analyzing the entire elution profile of the sample, while the PDI, which is a measure of the heterogeneity of the polymer sample, can be calculated as the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn .It is important to note that GPC provides relative molecular weight values, and the accuracy of the results depends on the quality of the calibration curve and the similarity between the sample and the standards. Other techniques, such as light scattering or viscometry, can be used in conjunction with GPC to obtain absolute molecular weight values and more accurate information about the polymer sample.