Expanding the application of stir bar sorptive-dispersive microextraction approach to solid matrices: Determination of ultraviolet filters in coastal sand samples.

This work describes a new method for the determination of organic compounds in solid samples based on the equilibrium desorption of the analytes in an aqueous phase followed by stir bar sorptive-dispersive microextraction (SBSDME). Sand samples, contaminated with UV filters due to bathing and recreational activities, were dispersed in an aqueous medium by using a coated stir bar with CoFe2O4@oleic acid magnetic nanoparticles. The UV filters were physically desorbed from the surface of the sand particles and rapidly adsorbed on the hydrophobic coating of the nanoparticles, which were retrieved by means of their magnetism after stopping the stirring. In this manner, both preconcentration of the analytes and clean-up were simultaneously accomplished without the requirement of any additional sample preparation steps. After extraction, the analytes were desorbed in ethanol and then analyzed by gas chromatography-mass spectrometry (GC-MS). The main variables involved in the extraction process (i.e., sorbent amount, extraction time, pH and ionic strength) were studied to provide the best extraction efficiencies and maximum enrichment factors. Under the selected conditions, the figures of merit of the proposed method were evaluated providing limits of detection in the low ng g-1 range, enrichment factors between 23 and 80, and relative standard deviations (RSD%) below 14% for all the target analytes. Matrix effects were observed in real costal sand samples and thus standard addition calibration was employed for quantification. The method was successfully applied to the analysis of UV filters in several coastal sand samples of different origin. This work expands the analytical potential of the novel SBSDME approach to the determination of organic compounds in solid matrices.