Characterization of Alginate Sodium Salt

Significance of the Topic

Alginate sodium salt is a versatile biopolymer widely employed as an emulsifier, stabilizer and thickening agent in food, cosmetic and pharmaceutical formulations. Accurate determination of its molecular weight distribution is critical for ensuring product consistency, performance and regulatory compliance.

Objectives and Study Overview

This study demonstrates a gel permeation chromatography method for characterizing the molecular weight profile of sodium alginate. Key aims include:

• Establishing reliable separation conditions on PSS SUPREMA columns
• Calibrating with pullulan standards for molar mass estimation
• Defining sample preparation and concentration guidelines for narrow and broad polydispersity samples

Methodology

Mobile phase consisted of water with 0.07 M disodium hydrogen phosphate at a flow rate of 1.00 mL/min and a column temperature of 25 °C. Sample concentration recommendations vary by molecular weight range:

• Narrow polydispersity index (PDI): 2 g/L for 100–10 000 Da; 1–2 g/L for 10 000–1 000 000 Da; ≤ 0.5 g/L for > 1 000 000 Da
• Broad PDI (> 1.5): 3–5 g/L across all molar mass ranges

Injection volume was set at 20 µL. Suitable column sets are specified for low, medium, high and ultrahigh molecular weight fractions, with options for three-column assemblies or single linear columns for each range.

Used Instrumentation

• GPC1100 refractive index detector
• PSS SUPREMA separation columns
• Pullulan calibration kit
• PSS WinGPC data processing software

Main Results and Discussion

The method produced clear elugrams for two sodium alginate samples, demonstrating baseline separation of molecular weight fractions. Pullulan-based calibration enabled reliable estimation of number average and weight average molecular weights, as well as polydispersity index. Observed distributions highlight differences in chain length and heterogeneity between commercial alginate batches.

Benefits and Practical Applications

• Rapid, reproducible profiling of alginate molecular weight
• Quality control in product development and manufacturing
• Optimization of viscosity and gelation properties for target applications

Future Trends and Potential Applications

Anticipated advances include integrating multi-angle light scattering detectors for absolute molecular weight determination, coupling GPC with hyphenated techniques such as mass spectrometry for structural insight, and deploying inline GPC systems for real-time process monitoring.

Conclusion

The outlined GPC method on PSS SUPREMA columns provides a robust approach for assessing sodium alginate molecular weight distributions, supporting critical quality attributes in food, cosmetic and pharmaceutical industries.