Novel Ultra-Sensitive Electrochemical Sensor Based on Screen-Printed Electrode Modified by 1,3-/1,4-Diazines for the Detection of Nitrobenzene in Solutions and Commercial Honey Samples

An efficient, highly sensitive electrochemical sensor for the detection of nitrobenzene in solutions and commercial honey samples was developed. The electrochemical behavior of nitrobenzene was investigated on the glassy carbon electrode and on screen-printed electrodes unmodified and modified with 1,3-/1,4-diazine compounds. The electrode modification process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The obtained results indicate a diffusion-controlled four-electron direct reduction process of nitrobenzene into hydroxylaminophenol in water solutions with enhanced cathodic currents on the diazine-modified screen-printed electrodes. This is probably contributed to the combination of complexation and collisional processes of diazines towards nitroaromatic compounds and also increased electroconductivity of the diazine-modified electrodes. The best electrochemical responses were obtained in square wave voltammetry mode by using the carbazolyl substituted diazines as a component of the sensitive layer, which was assembled by co-electropolymerized with unsubstituted carbazole on the electrode during 5 cycles. It allows one to additionally increase the effective surface area of the screen printed electrode and also to enhance the nitrobenzene peak current more than two times in comparison with the unmodified electrode as a result of the synergy effect. Under the optimized operating conditions, the reduction peak current was in linear dependence with the concentration of nitrobenzene in the range from 10-1000 µM. The low detection limit of the sensor estimated as 0.032 μM enables determining nitrobenzene in water and food samples. The developed electrochemical sensor was applied in the analysis of commercial honey samples using high performance liquid chromatography as the reference method. The results show the presence of trace amounts of NB in original honey samples. The analysis of spiked probes demonstrated the high precision of the proposed electrochemical sensor.