In-syringe magnetic dispersive µSPE exploiting magnetic almond shell biochar@ZIF-8 for parabens determination by UHPLC-UV

An in-syringe magnetic dispersive micro-solid phase extraction (MD-µSPE) system followed by UHPLC-UV analysis has been developed exploiting a hybrid sorbent based on magnetic alkali-activated almond shell biochar (MAASB), which is used as a support for in-situ growth of ZIF-8 (MAASB@ZIF-8), for the extraction and preconcentration of parabens (PBs) in environmental water and urine samples. Experimental designs were employed to optimize the pyrolysis conditions for biochar production, including temperature, heating rate, and residence time, and several parameters affecting extraction efficiency, e.g., pH, extraction time, ionic strength, eluent type, elution time and eluent volume. Under optimized conditions, the method showed detection limits between 0.05 and 0.09 ng mL⁻¹ for methyl, ethyl, propyl, and butyl paraben. The precision expressed as RSD (n = 3) showed intraday and interday ranges of 2.2–4.7 % and 2.6–4.3 %, respectively, demonstrating the good precision of the proposed methodology. Recovery studies were performed in the absence and presence of PBs spiked at different concentrations (10–30 ng mL⁻¹), yielding good recoveries in the range of 88–104 %. These results confirm that MAASB@ZIF-8 is an efficient sorbent for the determination of PBs, offering high porosity, magnetic responsiveness, and stability. Furthermore, the proposed method was evaluated with AGREE, ComplexMoGAPI, and BAGI metrics, evidencing its environmentally friendly approach, as well as the practicality of the method compared to previous works.