Optimizing Salt Concentration for Reliable Aqueous Size-Exclusion Chromatography of Water-Soluble Polymers

Area of Science:

• Polymer Chemistry
• Analytical Chemistry
• Biomaterials Science

Background:

• Size-exclusion chromatography (SEC) is vital for characterizing water-soluble polymers, but charged polymers (polyelectrolytes) present challenges due to non-size interactions.
• Salt addition to the mobile phase screens these interactions, yet the optimal concentration for reliable SEC is often undefined, with excess salt causing artifacts.

Purpose of the Study:

• To investigate the effect of sodium sulfate (Na2SO4) concentration on aqueous SEC of poly(ethylene oxide) (PEO) and sodium alginate.
• To determine the minimum effective salt concentration for obtaining reliable SEC/RALS data for a model anionic biopolymer.

Main Methods:

• Aqueous SEC with refractive index (RI) and right-angle light scattering (RALS) detection was employed.
• The study evaluated varying Na2SO4 concentrations using PEO as a reference and sodium alginate as a model polyelectrolyte.
• Qualitative and quantitative peak analyses were used to validate optimal mobile-phase conditions.

Main Results:

• PEO showed minor variations in elution volume and molecular weight with salt concentration, indicating sensitivity to mobile-phase conditions.
• Sodium alginate exhibited significant salt dependence, with low salt concentrations yielding broad, noisy peaks.
• A minimum Na2SO4 concentration of 6.25×10-3 M was identified as effective for producing clear, symmetric peaks for alginate.

Conclusions:

• Even nominally neutral polymers like PEO are influenced by mobile-phase salt concentration in SEC.
• Establishing the minimum effective salt concentration is critical for accurate SEC analysis of polyelectrolytes.
• The study provides a practical workflow for optimizing mobile-phase conditions in aqueous SEC of water-soluble polymers.