Abstract: Gel polish is an emerging cosmetic product for nail art, widely popular because of its advantages such as environmental friendliness and ease of application. However, further research has revealed that (meth)acrylates ((M)AAs) based reactive diluents, one of the gel polish’s main components, pose significant health risks. Given the high risk of (M)AAs, 2-hydroxyethyl methacrylate (HEMA) was added to the list of restricted substances in cosmetics by (EU) 2020/1682. Subsequently, trimethylolpropane triacrylate (TMPTA) was included in the list of concerned substances under the California Proposition 65. The aforementioned regulations have made HEMA and TMPTA become the market access red lines. Despite these restrictions, routine laboratory analysis continues to detect HEMA and TMPTA in a considerable proportion of gel polish samples, indicating that safety monitoring remains insufficient. Nevertheless, analytical methods for such risk substances remain scarce in China, leading to regulatory gaps and challenges to meet the demands of high-quality development in the gel polish industry. An analytical method for detecting eight (M)AAs in gel polish was established in this study. These (M)AAs include methyl methacrylate (MMA), 2-hydroxyethyl acrylate (HEA), HEMA, hydroxypropyl methacrylate (HPMA), tetrahydrofurfuryl methacrylate (THFMA), ethylene glycol dimethacrylate (EGDMA), triethylene glycol diacrylate (TEGDA) and TMPTA. Samples were diluted with ethyl acetate and precipitated with n-heptane, followed by freezing to remove interfering impurities such as prepolymers and polymers. In the optimization of solvent type, ethyl acetate was chosen as the diluent for its good solubility for gel polish. n-Heptane, with poor solubility for gel polish, was selected as the precipitant. A volume of 3 mL was chosen as the optimal amount of diluent to achieve good recovery. By examining the freezing time for impurity removal, 10 min was determined as the optimal duration. Chromatographic separation was performed using an Agilent VF-624ms capillary column (30 m × 0.25 mm × 1.40 μm) by GC-MS/MS. In order to improve the sensitivity and specificity of the analysis, multiple reaction monitoring (MRM) was performed using an electron impact ionization (EI) source. Highly characteristic ion pairs were selected based on the mass spectrometry fragmentation patterns, which minimized the matrix interference as much as possible. The eight target compounds exhibited some degree of matrix effects in the gel polish sample. Matrix-matched calibration was used as the quantitative method to eliminate the impact of matrix effects on analytical accuracy. The results showed good linearity for the eight target compounds in the range of 0.1-20 μg/mL, with correlation coefficients (r) all greater than 0.995 0. LOD of the method was 1 μg/g and LOQ was 5 μg/g for all compounds. The recoveries at low, medium, and high spiked levels ranged from 87.0% to 104.7%, demonstrating good accuracy. Excellent precision was achieved, as indicated by the low relative standard deviations (RSDs) between 0.28% and 0.94%. No significant fluctuation in peak areas was observed during the 46 h stability test, as evidenced by RSDs below 8% for all compounds, demonstrating excellent stability. The above validation results indicate that the established method is reliable and suitable for routine analysis. Twenty-two batches of commercially available gel polish were analyzed by the developed method in this study, with at least one (M)AAs detected in 21 batches of samples. Notably, the positive detection rates for HEMA and TMPTA, both explicitly listed as prohibited or restricted substances, reached as high as 68% and 73%, respectively, indicating that effective regulation is still needed for the gel polish industry to improve safety and compliance. This method offers high sensitivity, good selectivity, and accurate results, providing technical support for ensuring the safety and compliance of gel polish products, conducting risk monitoring, promoting high-quality development of cosmetics in China, and fostering the healthy growth of this emerging cosmetic sector.

Key words: gas chromatography-tandem mass spectrometry (GC-MS/MS), gel polish, methacrylate, acrylate, cosmetics