Abstract:

A method for analysis of oil-in-water （W/O） sunscreen formulations containing nano zinc oxide （ZnONPs） was established. The mixture of sodium dodecyl sulfate （SDS） and polyethylene glycol-polypropylene glycol copolymer （PEG-PPG-25/30） was used for extraction, and then the extracted sample was analyzed by ultrasound-assisted single particle inductively coupled plasma mass spectrometry （SP-ICP-MS）. This method enabled the determination of particle size distribution and particle number concentration of ZnONPs. The surfactant-polymer mixture could effectively break the stable structure of W/O emulsions through synergistic effects of electrostatic repulsion and steric hindrance, thus significantly enhancing the extraction efficiency and dispersion stability of ZnONPs. Key parameters such as pH value, ultrasonic treatment time, and dilution factor were optimized, and the optimized analytical conditions were as follows: pH of 7.0, ultrasonic processing for 30 min, and a range of particle testing concentration from 1.6×10⁸ to 1.2×10⁹ particles/L. Results of methodological validation indicated that the measured values for ZnONP standard materials were highly consistent with reference values; specifically, the detection limit for particle size was 7 nm while the detection limit for particle number concentration was 2.34×10³ particles/L. The spiked recovery was found to be 109.7%±3.5%, further confirming the excellent accuracy, sensitivity, and reproducibility in measurement. This work provided a reliable pre-treatment strategy to address challenges associated with extracting and accurately quantifying nanoparticles in complex matrices. The established method was straightforward in operation and rapid in analysis, making it suitable for high-precision and high-sensitivity detection of ZnONPs in W/O sunscreen products.

Key words: single particle inductively coupled plasma mass spectrometry, zinc oxide nanoparticle, surfactant, sunscreen