Magnetic ZnFe2O4 nanotubes for dispersive micro solid-phase extraction of trace rare earth elements prior to their determination by ICP-MS.

Magnetic ZnFe2O4 nanotubes (ZFONTs) with numerous pores on their walls were synthesized and characterized. They are shown to be a viable sorbent for dispersive micro-solid phase extraction of the trivalent ions of rare earth elements (REEs), specifically of lanthanum, praseodymium, europium, gadolinium, holmium and ytterbium. The specific surface area of ZFONTs is large (57 m2⋅g-1) and much bigger than that of ZnFeO4 nanoparticles (16 m2⋅g-1). It is shown that REEs are quantitatively retained on ZFONTs in the pH range of 7.0-9.0. The separation of the sorbent from the aqueous phase was achieved by an external magnetic field. Following elution with 0.5 mol⋅L-1 HNO3, REEs were quantified by inductively coupled plasma mass spectrometry. The main parameters influencing preconcentration and determination of the REEs were studied. Under optimum conditions, detection limits for REEs range from 0.01 (Ho) to 0.75 (La) pg⋅mL-1. Relative standard deviations are less than 6.5% (for n = 9; at 1.0 ng⋅mL-1). The method was applied to the determination of trace REEs in spiked biological and environmental samples and gave satisfactory results. Graphical abstract Schematic presentation of a new adsorbent for dispersive micro-solid phase extraction (DMSPE) combined with ICP-MS. Magnetic ZnFe2O4 nanotubes with many pores on their walls were used for preconcentration and determination of rare earth elements (REEs) in environmental and biological samples.