Molecular Weight Analysis

Molecular weight refers to the mass of a molecular relative to its constituent elements. Material's properties, such as mechanical properties, rheological properties, are influenced by its molecular weight and molecular weight distribution. Molecular weight plays an important role for material development, material selection, quality control during material processing. It is one of the basic data required for the study of specific polymerization reactions and the structure of specific polymers in the fields of polymer chemistry and polymer physics. In addition, molecular weight is also a primary parameter in the identification of biological samples such as proteins, peptides and polysaccharides.

Test Technologies

Relative molecular weight determination

• Gel Permeation Chromatography (GPC)

Gel permeation chromatography (GPC) is based on the separation mechanism of size exclusion. It is used to separate fat-soluble and water-soluble substances with smaller relative molecular mass through a stationary phase with molecular screening properties, The separation relative molecular mass ranges from several million to less than 100. It can also analyze polymer homologues with different molecular volumes and the same chemical properties. It has been widely used in the measurement of relative molecular weight and molecular weight distribution of polymers.

• SDS-PAGE

The addition of SDS to the electrophoresis system opens the hydrogen and hydrophobic bonds of the protein and binds to the protein molecule, making the electrophoretic mobility dependent only on the molecular size as a factor. Therefore, the molecular weight of the unknown can be obtained from the standard curve made by the logarithm of the molecular weight and mobility of the standard protein.

• Optical light scattering measurements

When a beam of light passes through the cylindrical sample tube, most of the light continues to travel after being transmitted, while other directions also emit scattered light due to the refractive index of the medium in the solution. Since the refractive index of the medium depends on the dielectric constant of the medium, which is the result of the density and concentration of the medium, the relationship between the dispersion of the solution and the molecular weight of the material can be known according to the Van-Hoff equation and the Willy expansion.

• Viscosity detection

Viscosity can be used to determine the molecular weight of material based on the certain relationship between the viscosity and the molecular weight of the materials.

Accurate molecular weight determination

• MALDI TOF-MS

Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI TOF-MS) can be used to obtain the absolute molecular weight, segment mass and end group mass of each polymer chain. The average molecular weight and polymerization dispersion data of polymers can also be obtained from MALDI TOF-MS spectra sensitively and quickly.

Test Capabilities

• Number-average molecular weight (Mn)
• Mass-average molecular weight (Mw)
• Z-average molecular weight (Mz)
• Polydispersity/Molecular weight distribution (MWD)

STEMart's expert molecular weight analysis can help you to understand the composition and properties of your materials and address processing and material failure issues throughout the material and product's lifetime. For more information about our molecular weight analysis, please contact us.