Determination of Ultratrace Levels of Cobalt (II) and Chromium (III) by Magnetic Dispersive Solid-Phase Extraction (SPE) Using Urea-Formaldehyde Polymer/Magnetite Nanoparticles with Flame Atomic Absorption Spectrometry (FAAS)

Abstract

A fast, selective and sensitive magnetic dispersive solid-phase extraction (SPE) method is presented for the first time for simultaneous preconcentration of ultra-trace levels of cobalt (II) and chromium (III) before their quantification by flame atomic absorption spectrometry (FAAS). Urea-formaldehyde polymer/magnetite nanoparticles (UFP/MNPs) were used as adsorbents. The prepared nano-adsorbent was assessed by x-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). The excellent magnetic properties of the prepared adsorbent promote rapid isolation of the analytes. A comprehensive study was performed on the extraction conditions and optimal levels of effective parameters were determined. Using the optimum conditions, linear dynamic ranges of 0.8–150 and 0.3-80 μg L⁻¹ were obtained for cobalt (II) and chromium (III), respectively. The limits of detection were 0.2 and 0.09 µg L⁻¹ for cobalt (II) and chromium (III). Intra-day and inter-day relative standard deviations (RSDs) were 3.8% and 5.7%, respectively. Adsorption isotherms were investigated and high adsorption capacities were obtained for the metal ions. The developed method managed to extract and quantify the analytes from unspiked and spiked environmental water samples from the Caspian Sea, Ardabil Balighli Chay River, and Ardabil tap water. The recoveries and relative standard deviations for the samples were from 98.2 to 103% and 0.2 to 5.7%, respectively. The results were validated by comparison with inductively coupled plasma – optical emission spectroscopy (ICP-OES) measurements.