Quantification of color intensity of diluted textile dye by visible near-infrared spectroscopy

Importance of the Topic

This application note demonstrates the use of visible near-infrared spectroscopy (Vis-NIR) to quantify the color intensity of textile dyes. Accurate color intensity measurement is essential in textile dyeing to ensure consistency, achieve desired appearance, and control product quality.

Objectives and Study Overview

The study aimed to:

• Develop a method to quantify dye color intensity using Vis-NIR spectroscopy as an alternative to UV-Vis reference analysis.
• Differentiate between dye types and suppliers.
• Identify impurities in undiluted dyes for raw material control.

Calibration used 19 aqueous dye solutions with known UV-Vis color strengths, and additional samples were reserved for external validation.

Methodology and Instrumentation

Measurements were performed in reflection mode on the Metrohm NIRS DS2500 Analyzer (400–2500 nm) for undiluted samples and in transmission mode on the NIRS XDS RapidLiquid Analyzer for diluted solutions. Spectral data were pretreated using a second derivative to correct baseline shifts. A Partial Least Squares (PLS) regression model with six factors was developed.

• Metrohm NIRS DS2500 Analyzer (reflection, 400–2500 nm)
• Metrohm NIRS XDS RapidLiquid Analyzer (transmission, 400–2500 nm)
• Disposable glass vials (4 mm) and sample cup holders
• Vision Air 2.0 Complete software for data acquisition and analysis

Main Results and Discussion

Identification of dye types and suppliers was achieved by selecting characteristic wavelength ranges: 1570–1720 nm for different dye types and 730–830 nm for samples from different suppliers. Impurities were detected by spectral differences in the 1750–1800 nm region. The PLS model for quantification in the 420–740 nm range yielded:

• Correlation coefficient R2 = 0.9846
• Standard Error of Calibration (SEC) = 108
• Standard Error of Cross-Validation (SECV) = 126
• Standard Error of Prediction (SEP) = 133

External validation confirmed accurate identification and quantification.

Benefits and Practical Applications

The combined Vis-NIR approach allows single-instrument analysis of multiple quality parameters within a 30-second scan. This method reduces costs and turnaround times compared to separate UV-Vis and NIR systems and supports rapid quality control in textile dyeing and raw material inspection.

Future Trends and Possibilities

Integration of Vis-NIR spectroscopy into process analytical technology (PAT) for real-time monitoring, development of more robust chemometric models with machine learning, and extension to other colorants and process streams present promising avenues for enhanced textile manufacturing control.

Conclusion

Vis-NIR spectroscopy offers a reliable, efficient, and multi-purpose alternative to UV-Vis methods for dye color intensity quantification, supplier differentiation, and impurity detection.

References

• Essential Chemical Industry. Colorants and applications.
• Wikipedia. Dyeing process overview.