Octyl coated cobalt-ferrite/silica core-shell nanoparticles for ultrasonic assisted-magnetic solid-phase extraction and speciation of trace amount of chromium in water samples

Abstract

In the present work, an organic-inorganic core-shell nanohybrid composed of octyl modified-silica coated cobalt ferrite nanoparticles (CoFe2O4@SiO2-C8) was synthesized, characterized and used as a magnetic nanoadsorbent for chromium speciation in environmental water samples. The procedure was based on the selective ultrasonic assisted-magnetic solid phase extraction (UA-MSPE) of non-charged chromium (VI)-ammonium pyrrolidine dithiocarbamate (APDC) chelate under the strong acidic solution prior to its detection by flame atomic absorption spectrometry (FAAS). Meanwhile, the total chromium ions chelated with APDC were quantitatively maintained on the sorbent at pH 6.0. The concentration of Cr (III) ions in the solution was calculated by the difference between the total Cr and the Cr (VI) level. The influences of various parameters on the extraction efficiencies including pH, ultrasonic time, amount of adsorbent and chelating agent, sample volume, and desorption conditions were studied and optimized. Good linearity was obtained in the ranges of 0.5–100 (R2 = 0.9993) and 0.4–100 µg L−1 (R2 = 0.9982) for Cr (VI) and Cr total, respectively. The limits of detection (LODs, 3δ/m) of the method were 0.15 µg L−1 and 0.13 µg L−1 for Cr (VI) and total Cr, respectively. Relative standard deviations (RSDs, n = 5) of the method for Cr (VI) and total Cr were 2.4% and 3.8%, respectively. The prepared adsorbent exhibited good chemical and mechanical stability, and selectivity towards Cr (IV) ions in the presence of other interfering ions. The developed procedure was successfully applied to chromium speciation in environmental water samples including tap, river, and wastewater samples with the recoveries in the range of 92.4–99.0%.