Cobalt content, solids content, specific gravity, and viscosity in cobalt octoate

Significance of the Topic

Vis-NIR spectroscopy represents an efficient approach for quality control in the coatings industry by enabling simultaneous, non-destructive measurement of multiple critical parameters in paint driers. This capability reduces analysis time and instrumentation requirements compared to traditional methods, supporting rapid decision-making during production and raw material qualification.

Goals and Overview of the Study

The study aimed to demonstrate that a Vis-NIR analyzer can accurately quantify cobalt content, solids content, specific gravity and viscosity of cobalt octoate paint driers in a single measurement. A feasibility evaluation was conducted by developing partial least squares (PLS) models correlating spectral data to established reference methods.

Methodology

Five cobalt octoate standards at 4 %, 6 %, 8 %, 10 % and 12 % cobalt were prepared, then diluted to yield 17 calibration samples. Spectra were acquired in transmission mode over 400–2500 nm using a 1 mm quartz cuvette. Data pre-processing included standard normal variate (SNV) correction to remove baseline offsets and scattering effects. Calibration models were built via PLS regression and validated through leave-one-out cross-validation.

Used Instrumentation

• NIRS XDS RapidLiquid Analyzer (Metrohm code 2.921.1410)
• 12.5 mm quartz cuvette, 1 mm path length (code 6.7401.200)
• Spacer for 12.5 mm cuvettes (code 6.7403.180)
• Vision Air 2.0 Software (code 6.6072.208)

Main Results and Discussion

• Cobalt content models based on the visible region (400–800 nm) achieved R² = 0.999, SEC = 0.08 % and SECV = 0.09 %.
• Solids content predictions over 800–2500 nm yielded R² = 0.999 with SEC = 0.24 % and SECV = 0.29 %.
• Specific gravity calibration produced R² = 0.997, SEC and SECV both = 0.003 g/cm³.
• Viscosity results showed R² = 0.999 with SEC = 9.3 mPas and SECV = 10.9 mPas using four PLS factors.
These outcomes highlight the strong linear correlation between spectral features and reference measurements, confirming the robustness of the Vis-NIR approach.

Benefits and Practical Applications of the Method

• Concurrent analysis of four parameters in a single, rapid measurement
• Reduction of sample handling and disposal compared to titrations and hydrometer tests
• Improved laboratory throughput and cost efficiency
• Non-destructive testing enabling sample archiving

Future Trends and Potential Applications

Expanding calibration libraries to include a wider variety of paint driers and additives will enhance model applicability. Integration of Vis-NIR probes for in-line monitoring could provide real-time process control. Advanced chemometric techniques and machine learning may further improve predictive accuracy and extend the approach to other coating properties and raw materials.

Conclusion

The application note demonstrates that Vis-NIR spectroscopy, combined with PLS modeling, offers a powerful and versatile solution for multi-parameter quality control of cobalt octoate paint driers. By covering 400–2500 nm, a single analyzer can replace multiple reference methods, streamlining operations and ensuring consistent product performance.

Reference

• ASTM D2373: Standard Test Method for Oil or Solvent-Reduced Alkyd Resin Solids
• ASTM D1644: Standard Test Methods for Drying, Curing, or Film Formation of Organic Coatings
• ASTM D5125: Standard Test Method for Cobalt Content in Paints and Coatings
• ASTM D2196: Standard Test Method for Rheological Properties of Non-Newtonian Materials by Rotational (Brookfield type) Viscometer
• ASTM D6122: Standard Test Method for NIR Spectroscopic Measurements
• Cu Ion-Selective Electrode Titration (AW TI CH1-1160-012014)