Spectral Analysis of Broad-Spectrum Sunscreens Using HPLC and a Photo Diode Array Detector

Importance of the Topic

Sunscreen formulations rely on multiple organic UV filters to protect human skin from harmful ultraviolet (UV) radiation. Analytical methods that provide fast, accurate separation and spectral verification of these filters are critical for quality control, regulatory compliance and formulation development. Photodiode array detection (PDA) paired with high-performance liquid chromatography (HPLC) enables simultaneous chromatographic separation and full-spectrum absorbance analysis to confirm peak purity and compound identity.

Study Objectives and Overview

This work demonstrates an HPLC-PDA method for rapid separation, spectral purity assessment and library-based identification of five common sunscreen UV filters and related impurities in both reference standards and over-the-counter (OTC) lotion samples. The study evaluates method repeatability, carryover and spectral coverage across UV and high-energy visible (HEV) ranges.

Methodology and Instrumentation

The method employs a Waters Alliance iS HPLC System coupled to a PDA detector (Detector Software version 1.4.0) under Empower 3 Software v3.8.0. Key parameters include:

• Column: XBridge Premier BEH C18, 2.5 µm, 4.6 × 150 mm
• Mobile phases: A = Water/0.1% formic acid; B = Acetonitrile/0.1% formic acid; gradient from 70% B to 95% B over 4 min
• Flow rate: 2.0 mL/min; column temperature: 40 °C; sample temperature: 20 °C; injection volume: 35 µL
• Sample prep: Reference standards at ~4 mg/mL in methanol; lotions dissolved in ethanol (5 mg/mL w/v), diluted 1:10 in methanol, filtered (0.2 µm)
• Run time: 7 min for standards; 15 min for lotions

Main Results and Discussion

The method baseline-resolved five UV filters (oxybenzone, avobenzone, octocrylene, octisalate, homosalate) and two related impurities in under 5.5 min with retention time repeatability ≤0.02% RSD and area RSD ≤0.19%. PDA spectra confirmed λmax values within UVC, UVB and UVA ranges; no significant absorbance was observed in the HEV blue region. Peak purity checks in Empower 3 showed spectral homogeneity above noise thresholds, and PDA library matching automatically identified each filter in lotion samples. Contour and three-dimensional plots illustrated broad UVB–UVA coverage for multi-filter formulations.

Benefits and Practical Applications

• Rapid, high-resolution separation of multiple sunscreen actives and impurities
• Spectral purity verification ensures accurate peak assignment and quality control
• Library-based UV filter identification streamlines analysis of complex formulations
• Minimal carryover and excellent repeatability exceed typical validation criteria

Future Trends and Possibilities

Advances in PDA detector sensitivity and data visualization will support analysis of next-generation UV and HEV filters, including metal oxide and polymeric systems. Coupling HPLC-PDA with mass spectrometry may enable simultaneous structural confirmation of novel actives. Artificial intelligence-driven spectral libraries could further automate filter identification in high-throughput QC environments.

Conclusion

The Alliance iS HPLC System with PDA detection provides a robust, reproducible platform for simultaneous separation, spectral purity assessment and library identification of broad-spectrum sunscreen filters. The method delivers fast run times, reliable performance and comprehensive UV coverage, making it well suited for routine QC of lotions and formulations.

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