Design and Development of a Nano sensor Modified by Molecularly Imprinted Polymers for Determination of Thiourea at Industrial Media

Thiourea (TU) as an organic additive is most commonly used in industrial processes of copper electro refining from acidified copper sulfate solutions. TU affects the structure of deposited cathodes via the mechanism of electrolytic reduction processes. Smooth and pure copper is obtained in case the reagent is in a proper concentration. An insufficient amount of a smoothing reagent has an equally detrimental effect that causes the nodulation phenomenon of the cathode. Since TU is consumed during electro refining by co-deposition with copper, it must be added to the electrolyte in a continuous way. Therefore, it is desirable to be able to measure the reagent concentration in the electrolyte [1]. In food industries, TU is known as a toxic and hazardous, and these effects seem to arise from a disturbance of carbohydrate metabolism that may be harmful for humans. Furthermore, TU has also been screened as allergenic and carcinogenic factors [2]. Different analytical techniques such as UV–Vis spectrophotometry, UV reflectance spectrometry, infrared spectrometry, chemiluminescence, Raman spectroscopy, chromatography and electrochemical methods [3] have been reported for the determination of TU in various samples. Electrochemical methods are suitable for determination of low levels of TU because of their high sensitivity and selectivity and inexpensive instrumentation. Development of various modified electrodes to achieve higher selectivity and sensitivity has been of interest, but there are few reports so far on the determination of TU using modifiers. Moreover, molecularly imprinted polymers (MIPs) are tailor made materials with selective recognition properties toward a chosen guest molecule or related compounds similar to that displayed by antibodies but without their experimental restrictions [4]. The MIPs were used to modify the carbon ceramic paste electrode 405 (CCE). In the present study, an electrochemical nanosensor based on MIP has been designed and developed for separation and determination of TU in industrial waste of Sarcheshmeh copper Inc. Co. The MIP synthesized by Methacrylic acid as a functional monomer, Ethylene glycol dimethacrylate as cross linker, 2,2-azobis(2-methyl propionitrile) as initiator and TU has been used as template. In the next stage Multiwall carbon Nano tube, Graphite, MIP and SiO2 solution used for making carbon ceramic electrode. The effect of different parameters such as, solution pH and time for pre-concentration of TU on electrode surface, also MIP and MWCNT amounts in preparation of electrode were investigated and optimized with statistical method of the Respond Surface Methodology (RSM). Optimized condition determined as MWCNT=3.3 mg, MIP= 12.3 mg, pH=8.0 and time of 26 min. Under optimal experimental conditions, DPVs of MIP/MWCNT/CCE was recorded to estimate the lower limit of detection and the linear range of TU. As expected, the oxidation TU signal increased upon the increase of TU concentration. Fig 1 clearly indicates that the plot of the reduction peak current against the TU concentration was linear in the two range of 0.05–5.0 nM and 50 -1100 nM. According to the method mentioned in Skoog et al. (1998), the lower detection limit, Cm, was calculated 0.12 pM by using the equation Cm=3sbl/m, where sbl is the standard deviation of the blank response and m is the slope of the calibration plot (0.2883 μA nM). The average voltammetric peak current and the precision estimated in terms of the coefficient of variation for repeated measurements (n = 15) of 0.12 pM TU at the MIP/MWCNT/CCE were 0.295 ± 0.007 μA and 2.4 %, respectively. Finally, performance of proposed procedure was evaluated to separation and determination of TU in industrial electrolyte of Sarcheshmeh copper Co. (Table 1). 406 Fig 1. Differential pulse voltammograms of MIP/MWCNT/CCE in a 0.1 M phosphate-buffered solution (pH 7.0) containing different concentrations of TU. Insets show the plots of the electrocatalytic peak current as a function of TU concentration in the range of 0.05-1100 nM. Table 1: Determination and recovery results of TU in industrial electrolyte using DPV calibration plots and with the nanosensor (MIP–MWCNT–CCE) Initial found (nM) Added (nM) Found (nM) Recovery (%) 155.1 10.0 168.6 102.1 20.0 173.9 99.3 50.0 208.65 101.7 100.0 251.21 98.51