Dye, diethylene glycol, water, and surfactant content in ink

Importance of Topic

In the ink production industry, maintaining consistent quality requires monitoring key formulation parameters—dye concentration, solvent levels, surfactant content and moisture. Traditional wet‐chemistry methods for these analyses are laborious, time‐consuming and require skilled personnel. Visible–near infrared (Vis–NIR) spectroscopy offers a rapid, non‐destructive alternative, enabling simultaneous determination of multiple components in a single measurement by untrained operators.

Objectives and Overview

This study aimed to develop and validate quantitative Vis–NIR methods for four critical ball‐pen ink parameters: dye (0.6–4.6 %), diethylene glycol (DEG, 12.5–29.8 %), surfactant (0.0–1.0 %) and water content (63.6–82.1 %). Twenty commercial blue ink samples served as the calibration set and eight independent samples for external validation.

Methodology and Used Instrumentation

The following instrumentation and configuration were employed:

• NIRS DS2500 Analyzer (Metrohm 2.922.0010) in transflection mode.
• Optically flat quartz transflection vessel, 1 mm path length (Metrohm 6.7401.000).
• Gold diffuse reflector, 1 mm path length (Metrohm 6.7420.000).
• Vision 4.03 chemometric software (Metrohm 6.6069.102).

Spectral data were recorded from 400 to 2350 nm depending on the analyte. Partial least squares (PLS) regression models were built using appropriate spectral pretreatments—second derivative, standard normal variate (SNV) or none—optimizing factors and wavelength ranges for each parameter.

Results and Discussion

Dye content was modeled over 420–800 nm with no pretreatment and two PLS factors, achieving R²=0.9961, SEC=0.0835 % and SECV=0.0949 %. DEG content between 2220–2300 nm used second‐derivative+SNV pretreatment and two factors (R²=0.9934, SEC=0.5037 %, SECV=0.5888 %). Surfactant content was predicted from 1350–2350 nm with a second‐derivative pretreatment and five factors (R²=0.9774, SEC=0.0368 %, SECV=0.1316 %). Water content was modeled in the 1300–1550 nm region using second‐derivative pretreatment and three factors (R²=0.9909, SEC=0.5571 %, SECV=0.9614 %). External validation on eight independent samples confirmed predictive accuracies within acceptable limits for all four analytes.

Benefits and Practical Applications

Vis–NIR spectroscopy streamlines ink quality control by:

• Providing rapid, simultaneous multi‐component analysis in under a minute.
• Eliminating reagents and complex sample preparation.
• Reducing operator training requirements.
• Supporting in‐process monitoring and batch release testing.

Future Trends and Potential Applications

Advances likely include integration of inline Vis–NIR probes for real-time production monitoring, expansion of chemometric models to colored inks and specialty formulations, deployment of handheld NIR devices for field QC and incorporation of machine learning algorithms to further improve prediction robustness and adaptivity.

Conclusion

The developed Vis–NIR methods demonstrate high accuracy and precision for quantifying dye, DEG, surfactant and water in ball‐pen inks. Adoption of this approach can significantly accelerate quality control workflows, reduce costs and improve consistency in ink manufacturing.

References

No additional literature references were provided in the source document.