Quality control of an active ingredient in hair spray using near-infrared spectroscopy

Importance of the Topic

Ensuring the correct dosing of active ingredients in hair sprays is critical for product performance and consumer safety. Traditional methods like LC-MS/MS are accurate but time-consuming and generate chemical waste. Implementing rapid, non-destructive techniques such as near-infrared spectroscopy (NIRS) can streamline quality control workflows, minimize environmental impact, and improve throughput in industrial and laboratory settings.

Objectives and Study Overview

This study aimed to develop and validate a NIRS-based method to quantify an active ingredient in hair spray formulations. Key objectives included:

• Constructing a calibration model correlating NIR spectral data with known active concentrations ranging from 0.0% to 8.4%.
• Evaluating model accuracy through calibration and cross-validation metrics.
• Comparing NIRS predictions with reference LC-MS measurements to assess reliability in detecting out-of-specification samples.

Methodology

Samples from five production batches were prepared by placing approximately 3 grams of hair spray into a transflection vessel equipped with a gold reflector. Spectral data were acquired over 400–2500 nm using the Metrohm DS2500 NIR analyzer. Spectra underwent pretreatment via second derivative transformation, and Partial Least Squares Regression (PLS) was applied to the 1590–1720 nm and 2090–2220 nm regions to isolate concentration-dependent spectral features.

Used Instrumentation

Key equipment and software employed in the study included:

• DS2500 NIR Analyzer (Metrohm code 2.922.0010)
• LiquidKit for DS2500 (6.7400.010)
• Vision Air 2.0 Complete software (6.6072.208)

Results and Discussion

The PLS model built with three latent variables achieved a calibration and cross-validation error (SEC and SECV) of 0.034% active ingredient. The correlation between NIRS-predicted concentrations and LC-MS reference values demonstrated strong linearity, confirming that spectral variations in the selected wavelength intervals directly correlate with active levels. The method reliably distinguished compliant samples from those outside specification limits, illustrating its suitability for rapid quality screening.

Benefits and Practical Applications

NIR spectroscopy offers several advantages over conventional chromatographic methods:

• Fast analysis time (results within seconds).
• No sample preparation required, preserving sample integrity.
• Non-destructive measurement allows sample reuse.
• Elimination of chemical reagents and associated waste.

This approach is ideal for high-throughput QC environments, enabling real-time monitoring of raw materials and final products without bottlenecks.

Future Trends and Opportunities

Advancements in NIR instrumentation and chemometric algorithms will further enhance sensitivity and robustness. Emerging inline and at-line NIRS solutions can integrate directly into production lines for continuous monitoring. The use of disposable vials and transmission-mode analyzers, such as the XDS RapidLiquid system, may simplify sample handling and reduce maintenance, broadening the deployment in cosmetic and pharmaceutical manufacturing.

Conclusion

The developed NIRS method provides a rapid, reliable, and eco-friendly alternative for quantifying active ingredients in hair sprays, reducing analysis time and waste generation compared to LC-MS. Its strong performance and operational advantages support its adoption in routine quality control to ensure consistent product efficacy.