Ultrasound-assisted dispersive solid-phase extraction of Ultratrace Fe(III) and Cr(III) from environmental waters using modified nanoporous MCM-41 as a novel adsorbent

A novel and highly selective method is presented for the preconcentration and determination of ultratrace Fe(III) and Cr(III) ions in environmental waters. The procedure integrates ultrasound-assisted dispersive solid-phase extraction (UA-DSPE) with flame atomic absorption spectrometric (FAAS) detection, using a newly engineered adsorbent. This material, acetylacetone-functionalized aminopropylated MCM-41 (acacAmpMCM-41), was specifically synthesized via covalent modification of mesoporous silica to impart tailored chelating affinity for trivalent metal cations. All parameters influencing extraction efficiency, including sample pH, adsorbent dosage, eluent composition, ultrasonication time, and sample volume, were systematically investigated and optimized. Under the established optimal conditions, quantitative adsorption was achieved within 20 min, followed by complete analyte recovery using 2.5 mL of 1.0 mol L −1 HNO 3 in a 10- desorption step. The method demonstrates excellent analytical performance, with low detection limits of 0.72 μg L −1 for Fe(III) and 0.44 μg L −1 for Cr(III), high precision (relative standard deviation <2.7%, n = 7), and quantitative recoveries in the range of 95–104% with a preconcentration factor of 100. The synthesized acacAmpMCM-41 exhibits high adsorption capacities of 29.6 and 32.4 mg g −1 for Fe(III) and Cr(III), respectively, and exceptional selectivity in the presence of common interfering ions. Successful application of the method to various environmental water samples (tap, river, and seawater) validates its practicality and robustness. This work establishes the acacAmpMCM-41-based UA-DSPE-FAAS protocol as a sensitive, reliable, and efficient tool for monitoring ultratrace levels of these ecologically significant trivalent metals in complex aqueous matrices.