SEC Analysis of Carboxymethyl Cellulose

Significance of the Topic

Carboxymethyl cellulose (CMC) is a key polymer in the food and pharmaceutical industries for viscosity control and product texturization. Small variations in its molecular weight distribution can critically alter performance, making sensitive analytical techniques essential for quality control and product optimization.

Objectives and Study Overview

The study aimed to resolve subtle differences in molecular weight among CMC samples with identical viscosity grades. By employing size exclusion chromatography (SEC) on Agilent PL aquagel-OH columns connected in series, the work sought to demonstrate high-resolution profiling over a broad molecular weight range (10^4–10^7 Da).

Methodology and Instrumentation

Instrumentation and conditions

• System: Agilent 1260 Infinity GPC/SEC
• Columns: two PL aquagel-OH 60 (8 µm, 300 × 7.5 mm) in series with one PL aquagel-OH 40 (8 µm, 300 × 7.5 mm)
• Eluent: 0.5 M Na₂SO₄
• Flow rate: 1.0 mL/min
• Detection: Refractive index (RI)

Calibration was achieved using pullulan molecular weight standards.

Main Results and Discussion

Chromatograms of three CMC variants revealed distinct elution profiles despite equal viscosity. Slight retention time shifts corresponded to differences in molecular weight distribution. The high pore volume and column efficiency (>35 000 plates/m) of PL aquagel-OH phases enabled clear separation of closely related polymer species.

Benefits and Practical Applications

SEC with PL aquagel-OH columns offers:

• Enhanced discrimination of polymer batches beyond viscosity measurements
• Improved quality assurance in food and pharmaceutical formulations
• Ability to detect minor changes in production or raw material quality

Future Trends and Potential Applications

Advances may include:

• Integration of multi-angle light scattering (MALS) detectors for absolute molecular weight determination
• High-throughput screening of water-soluble polymers
• Expanded use in characterizing copolymers and charged biopolymers

Conclusion

SEC analysis using Agilent PL aquagel-OH columns provides a robust approach to detect minor molecular weight variations in CMC, supporting stringent quality control where viscosity alone is insufficient.

Reference

Agilent Technologies Inc. Application Note 5991-5792EN, "SEC Analysis of Carboxymethyl Cellulose", April 30, 2015.