Insitu ultrasound-assisted synthesis of Fe3O4nanoparticles with simultaneous ion co-precipitation for multielemental analysis of natural waters by total reflection X-ray fluorescence spectrometry

Abstract

In this work, in situ ultrasound-assisted magnetite synthesis with simultaneous ion co-precipitation (UAMS-SIC) was applied to magnetic solid-phase extraction (MSPE) of Cu, Zn, Ge, As, Se, Re, Au, Hg, Tl, Bi and Pb. The magnetic solid phase (MSP) enriched with metal ions was directly analyzed by total reflection X-ray fluorescence (TXRF). Magnetite nanoparticles (Fe₃O₄ NPs) were synthesized by sonochemical treatment of a solution containing Fe(II) and Fe(III) in the presence of target analytes so that these are trapped by occlusion or surface adsorption during the formation of Fe₃O₄ NPs. In situ synthesized Fe₃O₄ NPs were easily separated from the aqueous matrix by applying an external magnetic field, and hence, no filtration or centrifugation steps were necessary. A 10 μL aliquot of MSP was deposited onto a sample quartz glass siliconized carrier and analyzed by TXRF, thus avoiding the elution step. The effect of the Fe(II) : Fe(III) molar ratio, total mass of Fe in the MSP, ultrasound amplitude, time and interfering ions on the extraction efficiency of the metal ions was investigated. Detection limits ranged from 0.3 to 26 μg L⁻¹ depending on the metal ion. Enrichment factors (EFs) in the range 8–180 were achieved. A recovery study carried out on spiked samples showed recoveries in the range 89–109% with relative standard deviations below 10% (N = 5). An effective, fast and sensitive procedure that can be used for field analysis is accomplished. A comprehensive characterization of in situ synthesized Fe₃O₄ NPs was carried out by atomic force microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Finally, a co-precipitation mechanism for trace metal ions with this novel synthesis of nanosized magnetite is approached using the Berthelot–Nernst and the Doerner–Hoskins laws.