Determination of sun protection factor in creams using visible near-infrared spectroscopy

Significance of the Topic

Effective sunscreen products are essential to reduce the risk of skin damage and cancer caused by ultraviolet radiation. Reliable determination of SPF is a critical quality control measure in the cosmetics industry, ensuring product safety and performance.

Aims and Study Overview

This study evaluates the application of visible near-infrared spectroscopy (Vis-NIRS) for rapid, non-destructive measurement of sunscreen SPF in commercial cream formulations. The goal is to develop a fast method requiring minimal sample preparation.

Methodology

A set of 14 sunscreen creams covering SPF values from 10 to 50 were analyzed. Approximately 1 g of each sample was loaded into a DS2500 Slurry Cup with a 1 mm gold diffuse reflector. Spectra were recorded in transflection mode over 400–2500 nm. Pretreatment included second derivative and standard normal variate (SNV). A Partial Least Squares (PLS) regression model with four factors was calibrated and internally cross-validated.

Used Instrumentation

• NIRS DS2500 Analyzer (400–2500 nm)
• DS2500 Slurry Cup accessory
• 1 mm gold diffuse reflector
• Vision Air 2.0 software suite

Main Results and Discussion

The PLS model achieved high predictive performance with R² = 0.9932, SEC = 1.30 SPF units, and SECV = 2.20 SPF units. Spectral trends clearly correlate absorbance features with SPF levels, demonstrating Vis-NIRS capability for accurate quantification.

Benefits and Practical Applications

• Rapid analysis (<30 s) without sample preparation
• Non-destructive measurement preserving samples
• No chemical waste generation
• Easy cleaning and rapid throughput
• Potential for simultaneous measurement of moisture and additives

Future Trends and Possibilities

Advancements may include integration with production-line monitoring, development of portable NIRS devices for on-site QC, and enhanced chemometric algorithms for multi-parameter analysis of personal care products.

Conclusion

Visible NIRS on the Metrohm DS2500 platform offers a fast, reliable, and eco-friendly approach for SPF determination in creams. The method supports quality control workflows with minimal operational complexity and high analytical performance.