Characterization of Hydroxyethyl Starch

Significance of the Topic

Hydroxyethyl starch (HES) is a chemically modified polysaccharide widely used in pharmaceutical and biomedical applications, particularly as a plasma volume expander. Precise determination of its molecular weight distribution and polydispersity is critical for ensuring efficacy, safety and batch-to-batch consistency.

Objectives and Study Overview

This application note describes the development and optimization of a size-exclusion chromatography (SEC/GPC) method for comprehensive characterization of HES. Key aims include establishing ideal chromatographic conditions, sample preparation guidelines and calibration strategies to achieve reliable molecular weight profiling.

Methodology and Protocol

Aqueous SEC was conducted using PSS SUPREMA columns and a sodium nitrate 0.1 M mobile phase. Chromatographic parameters were maintained at 1.00 mL/min flow rate and 25 °C. Detection was performed with a Shodex-RI71 refractive index detector. Calibration was based on an HES standard kit and data were processed in PSS WinGPC.

Recommended sample concentrations and injection settings:

• Narrow PDI samples:
  • 100–10 000 Da: 2 g/L
  • 10 000–1 000 000 Da: 1–2 g/L
  • > 1 000 000 Da: ≤ 0.5 g/L
• Broad PDI (>1.5) samples (all molar masses): 3–5 g/L
• Injection volume: 20 µL

Column selections for different molecular weight ranges:

• Low Mw: P/N 206-0001 (set of 3) or sua083005lis (1 linear)
• Medium Mw: P/N 206-0002 (set of 3) or sua083005lim (1 linear)
• High Mw: P/N 206-0003 (set of 3) or sua083010lxl (1 linear)
• Ultrahigh Mw: P/N 206-0004 (set of 3) or sua083010luh (1 linear)

Instrumentation Used

• Chromatography system with PSS SUPREMA columns
• Refractive index detector: Shodex-RI71
• Data acquisition and analysis software: PSS WinGPC
• Calibration kit: Hydroxyethyl starch standards

Main Results and Discussion

Under these conditions, HES samples exhibited well-resolved, reproducible elution profiles across the full molecular weight range. Calibration using the dedicated HES kit produced accurate weight-average molecular weights (Mw) and narrow polydispersity indices (PDI) when sample concentrations and column sets were matched to target Mw ranges.

Benefits and Practical Applications

This SEC method enables rapid quality control in research and manufacturing environments. It provides:

• High reproducibility and resolution of HES size distribution
• Tailored protocols for different PDI and Mw ranges
• Straightforward implementation for batch release testing and formulation development

Future Trends and Possibilities

Advances may include coupling SEC with multi-angle light scattering (MALS) or viscometric detectors to obtain absolute molecular weights and branching information. Integration of real-time process monitoring and miniaturized column formats could further enhance throughput in industrial analytics.

Conclusion

The described GPC/SEC approach on PSS SUPREMA columns, combined with refractive index detection and tailored sample preparation, offers a robust platform for in-depth characterization of hydroxyethyl starch. Its flexibility and reliability make it an asset for analytical laboratories focused on polymer quality control and research applications.