Electrochemical detection of Cr(III) and Cr(VI) in solution by using ZrO2 modified magnetic nanoparticles by redox probes

Abstract

Herein, modified Fe3O4 magnetic nanoparticles by ZrO2 (MNPZs) were prepared by co-precipitation method. Prepared MNPZs were characterized with XRD, SEM, EDX, TEM, FTIR and VSM techniques. In addition, a modified magnetic carbon paste electrode (CPE) by MNPZ was prepared, and its interaction with Cr(III) and Cr(VI) ions was investigated in the presence of [Fe(CN)6]3-/4- and PBQ/H2Q redox probes via CV and EIS. An electrochemical technique based on observed behavior of redox probes with accumulated each forms of chromium was developed for speciation of Cr(III) and Cr(VI) in this work. Accumulated Cr(III) on CPE/MNPZ showed electrostatic attraction toward [Fe(CN)6]3-/4- redox probe and accumulated Cr(VI) showed a blocking behavior toward PBQ/H2Q redox probe. According to different behaviors of Cr(III) and Cr(VI) at electrode interface in the presence of redox probes, a new calibration for each forms of chromium ions and an entire protocol for Cr speciation are proposed based on voltammetry and impedimetry. After optimization of affecting experimental parameters on the electrode response, linear calibration curves from 1.0 × 10-9 to 1.0 × 10-3 M with sensitivity as 3.41 μA/M and detection limit (DL) as 8.1 × 10-10 M, and from 1.0 × 10-9 to 1.0 × 10-6 M with sensitivity as 4.07 kΩ/M and DL as 6.9 × 10-11 M, were obtained for Cr(III) by using [Fe(CN)6]3-/4- as a redox probe in CV and EIS methods, respectively. Also, linear calibration curves from 5.0 × 10-9 to 1.0 × 10-4 M with sensitivity as 1.79 μA/M and DL as 5.3 × 10-10 M, and from 1.0 × 10-9 to 5.0 × 10-5 M with sensitivity as 7.05 kΩ/M and DL as 4.5 × 10-10 M, were observed for Cr(VI) when use PBQ/H2Q as redox probe in CV and EIS methods, respectively.