Purity, degree of substitution (DS), and moisture content of carboxymethyl cellulose (CMC)

Significance of Topic

Carboxymethyl cellulose (CMC) is a versatile cellulose ether extensively used in pharmaceuticals, cosmetics, paints and coatings due to its thickening, binding and disintegrant properties. Critical quality attributes such as purity, degree of substitution (DS) and moisture content govern its performance and compliance in regulated industries. Traditional wet-chemical analyses (ASTM D1347, D1439) are accurate but time-consuming, creating a need for faster, user-friendly methods.

Aims and Study Overview

This study evaluates the capability of visible-near infrared (Vis-NIR) spectroscopy to simultaneously quantify three key parameters of CMC: purity (97–100 %), DS (0.5–0.9) and moisture content (2–7 %). The goal was to develop robust calibration models and verify their predictive power using independent validation sets.

Methodology and Instrumentation

Samples of CMC with varied purity, DS and moisture levels were placed in glass vials and measured in reflectance mode over the full Vis-NIR range (400–2500 nm). Spectral pretreatment involved a second-derivative filter (10 nm segment). Partial least squares (PLS) regression models were built using Metrohm Vision 4.03 software and externally validated to assess accuracy and precision.

Used Instrumentation

• NIRS DS2500 Analyzer (reflection mode)
• NIRS DS2500 Iris sample adapter
• Vision 4.03 chemometric software

Main Results and Discussion

The purity model (PLS, 3 factors) achieved R² = 0.9836 and SEP = 0.105 %. The DS model (PLS, 5 factors) yielded R² = 0.9817 and SEP = 0.0147. The moisture model (PLS, 3 factors) showed moderate performance with R² = 0.8401 and SEP = 0.499 %. External validation demonstrated mean prediction errors below 0.05 % for purity, 0.02 for DS and 0.2 % for moisture, confirming the models’ reliability.

Benefits and Practical Applications

Vis-NIR spectroscopy enables rapid, multi-parameter analysis in a single scan, reducing sample preparation and labor. The method can be performed by non-specialized personnel, accelerates quality control in production environments and lowers reliance on reagents and waste-generating procedures.

Future Trends and Opportunities

Integration of real-time NIR probes into continuous manufacturing lines will further enhance process control. Advances in machine learning may improve spectral interpretation and expand the approach to other cellulose derivatives. Portability and miniaturized NIR devices promise on-site, real-time monitoring across diverse industrial settings.

Conclusion

Vis-NIR spectroscopy provides a fast, reliable alternative to conventional lab methods for determining purity, DS and moisture in CMC. High accuracy for purity and DS and acceptable moisture precision support its adoption for quality assurance in pulp, paper and related industries.

References

• Metrohm Application Note NIR-31: Vis-NIR Spectroscopy for CMC Analysis
• ASTM D1347: Standard Test Method for Carboxymethyl Cellulose Purity
• ASTM D1439: Standard Test Method for Degree of Substitution of CMC