New Test Methods for Extractables in No-Wipe Topcoat Gel Polish: Extraction and Quantitation of Uncured Monomers After UV Curing

Background: Nail gels are decorative fingernail coatings based on (meth)acrylates that are photopolymerized on the nail surface. After polymerization, these coatings typically retain an uncured layer of monomers at the air interface due to oxygen inhibition, which may pose a risk of skin sensitization unless removed. No-wipe topcoats are formulated to address this issue by curing fully; however, no standard test method exists to verify a complete cure. This study presents a method to quantify residual uncured traces of several common nail gel monomers extracted from polymerized commercial no-wipe nail gels. Method: Commercially available no-wipe nail gels were formed into films of controlled thickness and polymerized using a standard UV-curing nail lamp. Solvent extraction was employed to eliminate residual uncured monomers, namely diethylene glycol dimethacrylate (DEGDMA), isobornyl acrylate (IBOA), and 2-hydroxyethyl methacrylate (HEMA). These monomers were quantified utilizing GC-FID and HPLC techniques. Method validation was conducted with samples of known monomer identity and concentration, thereby establishing specificity, linearity, precision, and detection limits. Results: Validated test protocols were established for the analysis of residual uncured traces of three commonly used monomers in nail gel coatings. In all instances, levels of monomer residue in a cured gel coating were found to range from 56 µg/g to 800 µg/g. Tests conducted on commercial products indicated that levels of these monomers fell within the expected normal ranges for such products. Conclusions: Through the utilization of two chromatographic techniques, three analytical methods were established for the simultaneous determination of ingredient concentrations and residual monomer quantities in unreacted bulk formula and cured UV-gel film. These methods and the resultant data facilitate the evaluation of curing completeness, which is essential for product development and safety assessments.