Electrochemical detection of bromate in food at MCWNT/Ni/Pc and MWCNT/Co/Pc modified electrode

Abstract

Bromate in food and water has been linked to cancer risks for lifetime exposures, and the present techniques for its detection have significant limitations that necessitate the development of new and more efficient approaches. The study describes the synthesis and characterization of CoPcMWCNTs and NiPcMWCNTs nanocomposites prior to the modification of a glassy carbon electrode for bromate detection. The two nanocomposites were prepared from cobalt or nickel nanoparticles, phthalocyanine and functionalized multiwalled carbon nanotubes fMWCNTs. The successful synthesis of the nanoparticles and the nanocomposites were confirmed by the microscopic and spectroscopic techniques such as the X-ray diffraction spectroscopy (XRD), UV-visible spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The synthesized nanoparticles and nanocomposites were used to modify the glassy carbon electrode (GCE). The electrochemical characterization of the bare GCE and the modified electrodes (GCE-Co, GCE-Ni, GCE-MWCNTs, GCE-CoPcMWCNTs, and GCE-NiPcMWCNTs) was performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques in 5 mM ferricyanide/ferricyanide ([Fe(CN)6]4-/3-) prepared in 0.1 M phosphate-buffered solution PBS (pH 7). The CV results showed that the GCE-CoPcMWCNTs, and GCE-NiPcMWCNTs nanocomposites exhibited the highest current response (259.1 & 457.0 μA) and specific capacitance (7.47 & 6.80 F/g), respectively, than the other nanomaterials. A similar trend was obtained in the EIS experiment with the GCE-CoPcMWCNTs, and GCE-NiPcMWCNTs nanocomposites having lower charge transfer resistance (Rct) than the individual nanomaterials. The nanocomposites' higher electronic properties as compared to those of the individual nanomaterials demonstrated that the synergy created by combining the nanomaterials during composite production resulted in improved electron transport capabilities. The electroanalysis of the analyte (bromate) at the CoPcMWCNTs, and GCE-NiPcMWCNTs using cyclic voltammetry (CV) and EIS revealed that both CoPcMWCNTs, and GCE-NiPcMWCNTs exhibited higher reduction peak currents (Ipc) and faster electron transport, thus having better electrocatalytic behaviour. According to scan rate studies, scan rate (v) is directly proportional to the bromate cathodic current responses (Ipc) at GCE-CoPcMWCNTs and GCE-NiPcMWCNTs. Based on the linear relationship between reduction peak currents (Ipc) and the square root of the scan rate (v1/2), the bromate reduction mechanism at GCE-CoPcMWCNTs and GCE-NiPcMWCNTs was diffusion controlled.

Using EIS technique, a LoD of 11.54 and 21.81 μM was obtained for the GCE-CoPcMWCNTs and GCE-NiPcMWCNTs over linear dynamic ranges (LDRs) of 48-167 and 48-200 μM, respectively. The sensitivities of the sensors were 125.5 and 485.6 μA μM-1, respectively. Whereas, with square wave voltammetry (SWV) technique, an LoD of 8.87 and 3.09 μM was obtained for the GCE-CoPcMWCNTs and GCE-NiPcMWCNTs over linear dynamic ranges (LDRs) of 24-149 and 24-111 μM, respectively. The sensitivities offered by the two sensors were 485.6 and 1290 μA μM-1, respectively. The two sensors demonstrated a good selectivity towards the bromate detection in the presence of interfering species (K+, Na+, NH4+, SO42−, Cl−, ClO3−, and CO32−), except for IO32- and Mg2+. Both sensors offered the same performance regarding stability, reproducibility, selectivity and real sample analysis. Importantly, the two sensors were effectively used for bromate determination in bread samples with a good recovery, demonstrating the practical application of the sensors to detect bromate in food.