Overcoming Field-Amplification Decay: A Counterflow Electroextraction Strategy for Direct, Fast, and Exhaustive Enrichment of Per- and Polyfluoroalkyl Acids from Cosmetic Matrices.

Per- and polyfluoroalkyl acids (PFAAs) in cosmetics pose significant human health risks. However, analytical methods for their monitoring remain scarce due to matrix interference, as the direct, fast, and exhaustive enrichment of trace targets from complex semisolid and solid cosmetic matrices is rather challenging. To address this gap, we developed a novel counterflow-sustained field amplification nonaqueous miscible liquid-liquid electroextraction (CSFA-NMLEE) technique. The CSFA strategy dynamically sustains a strong electric field in the sample donor phase via counterflow electrolyte replenishment, overcoming intrinsic time-dependent field decay in conventional techniques. This mechanism effectively disrupts analyte-matrix interactions, releasing PFAAs from semisolid and solid matrices, while simultaneously expelling comigrating interferents and compressing the enriched analyte zone. This integrates exhaustive electroextraction, efficient cleanup, and enrichment within a single 8 min step. Coupled with LC-MS/MS, the method enables rapid analysis of 20 PFAAs, requiring minimal sample (20 mg) and a low-cost device, while achieving high accuracy (88.5-104.6%), precision (RSD < 9.4%), and low detection limits (0.025-0.6 μg·kg-1) across diverse cosmetic matrices. Crucially, it facilitated the first investigation of PFAA migration from packaging materials into cosmetic products, revealing significant transfer of perfluorobutanesulfonate (0.6-14.17 μg·kg-1) and perfluorobutyric acid (0.15-1.39 μg·kg-1) from the majority of tested materials. These findings identify packaging as a previously unrecognized exposure source, and the overall work provides a critical and robust tool for exposure assessment against this emerging contamination pathway.