Dispersive solid-phase extraction based on oleic acid-coated magnetic nanoparticles followed by gas chromatography–mass spectrometry for UV-filter determination in water samples

A sensitive analytical method to concentrate and determine extensively used UV filters in cosmetic products at (ultra)trace levels in water samples is presented. The method is based on a sample treatment using dispersive solid-phase extraction (dSPE) with laboratory-made chemisorbed oleic acid-coated cobalt ferrite (CoFe2O4@oleic acid) magnetic nanoparticles (MNPs) as optimized sorbent for the target analytes. The variables involved in dSPE were studied and optimized in terms of sensitivity, and the optimum conditions were: mass of sorbent, 100 mg; donor phase volume, 75 mL; pH, 3; and sodium chloride concentration, 30% (w/v). After dSPE, the MNPs were eluted twice with 1.5 mL of hexane, and then the eluates were evaporated to dryness and reconstituted with 50 μL of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) for the injection into the gas chromatography–mass spectrometry (GC–MS). Under the optimized experimental conditions the method provided good levels of repeatability with relative standard deviations below 16% (n = 5, at 100 ng L−1 level). Limit of detection values ranged between 0.2 and 6.0 ng L−1, due to the high enrichment factors achieved (i.e., 453–748). Finally, the proposed method was applied to the analysis of water samples of different origin (tap, river and sea). Recovery values showed that the matrices under consideration do not significantly affect the extraction process.