Magnetic solid-phase extraction based on Ni-Al layered double hydroxide/magnetite nano-hybrid for speciation of Mn(vii)/Mn(ii) in water samples by FAAS

A novel magnetic solid-phase extraction (MSPE) method applying a nanosorbent based on an Ni-Al layered double hydroxide/magnetite nano-hybrid (Ni-Al LDH/Fe3O4) was developed for the preconcentration and speciation of Mn(VII)/Mn(II) in aqueous solutions via flame atomic absorption spectrometry. The synthesized Ni-Al LDH/Fe3O4 nano-hybrid was characterized via X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The prepared nanosorbent can selectively extract Mn(VII) ions due to the negative charge of MnO4-ions. The total Mn and thus indirectly Mn(II) were determined after pre-oxidation of Mn(II) to Mn(VII) with an acidic solution of potassium periodate. Various parameters affecting the extraction recovery such as the amount of Ni-Al LDH/Fe3O4 nano-hybrid, pH of the solution, extraction time, eluent conditions, sample volume and interfering ions were investigated. Applying the optimum conditions, the developed method was successfully used for the speciation of Mn(VII)/Mn(II) species in various water samples with a linear dynamic range of 0.4-150 ng mL(-1) (R-2 = 0.9998) and a detection limit of 0.1 ng mL(-1). The method precision was evaluated with six replicates at a concentration level of 80 ng mL(-1), and a relative standard deviation of 3.3% was obtained. Furthermore, the method was applied for the determination of Mn(VII)/Mn(II) species in spiked real water samples and relative recoveries in the range of 93.6% to 103.3% were obtained.