Qualification of droplet morphology in hair conditioner by Vis-NIR spectroscopy

Significance of the Topic

Hair conditioner performance depends critically on droplet size distribution, which influences product efficacy, texture and sensory attributes. Rapid, non-destructive methods for monitoring droplet morphology are essential for quality control in cosmetic manufacturing.

Objectives and Overview of the Study

The primary aim of this application note was to develop and validate Vis-NIR spectroscopic methods for:

• Identifying whether a hair conditioner sample is unprocessed or processed.
• Qualifying droplet sizes against defined thresholds (5–20 µm vs. 5–50 µm).

Two intermediate conditioner formulations were provided: sample A (unprocessed, 5–50 µm) and sample B (processed, 5–20 µm). Models were built and tested using independent validation sets.

Methodology and Instrumentation

Diffuse reflectance spectra were collected from 400 to 2500 nm using a Metrohm NIRS DS2500 Analyzer with variable spot size. Samples in disposable vials were scanned and spectra pre-treated by second derivative (segment = 10 nm, gap = 0 nm) to minimize baseline effects. Two types of chemometric models were created in Vision Air Complete software:

• Identification model to classify samples as A or B (wavelength regions 416–1080 nm, 1120–2480 nm).
• Qualification model to assess droplet size relative to the threshold (region 1380–1404 nm).

The software automatically executed classification and qualification and reported results in seconds.

Results and Discussion

Raw Vis-NIR spectra of samples A and B showed overlapping features but were resolved by second derivative analysis. Classification models achieved clear separation between unprocessed and processed formulations. Qualification models successfully discriminated droplet sizes, with unprocessed samples failing the size threshold and processed samples passing both identification and qualification steps.

Benefits and Practical Applications

Vis-NIR spectroscopy offers:

1. Rapid, real-time quality control without sample destruction.
2. Minimized reliance on labor-intensive microscopy or laser diffraction.
3. Automated, user-friendly analysis with immediate feedback.

This approach can be integrated into production lines to ensure consistent product quality and reduce analytical bottlenecks.

Future Trends and Applications

Advances in NIR instrumentation and chemometrics may enable:

• Inline monitoring of emulsion stability and droplet coalescence dynamics.
• Expansion to other cosmetic emulsions and pharmaceutical formulations.
• Integration with process analytical technology (PAT) frameworks for closed-loop control.

Conclusion

The study demonstrated that Vis-NIR spectroscopy, combined with derivative pretreatment and chemometric modeling, reliably identifies conditioner formulations and qualifies droplet morphology. This fast, non-destructive method enhances quality assurance workflows in cosmetic production.

Instrumentation Used

• Metrohm NIRS DS2500 Analyzer
• NIRS DS2500 Iris accessory
• Vision Air 2.0 Complete software