| This paper is to apply nano-materials, such as graphene, gold nanoparticles, organic polymeric membranes and their composite materials to the construction of electrode, which is a new direction for chemically modified electrodes and has an important significance to improve the sensitivity and selectivity of analysis. Based on this, different novel chemically modified electrodes were constructed and applied to some food analysis (β-agonists, synthetic antioxidants and spice). The main contents and conclusions are as follows:1. An electrochemical method involving a gold nanoparticle modified glassy carbon electrode (AuNPs/GCE), was researched and developed for the simultaneous analysis of three (32-agonists, ractopamine (RAC), salbutamol (SAL) and clenbuterol (CLB). The three analytes were electrocatalytically oxidized at the AuNP/GCE, which enhanced the oxidation peak current and influenced the shift of the oxidation potentials to lower values in comparison with the analysis involving only the GCE. The peak currents associated with RAC, SAL and CLB measurements were linear as a function of their concentrations (ranges within0.005～0.075μg mL-1,0.010～0.150μg mL-1and0.004～0.064μg mL-1for RAC, SAL and CLB, respectively); the detection limits for RAC, SAL and CLB were2.4,5.8and2.6ng￣mL-1, respectively. The differential pulse stripping voltammetry (DPSV)voltammograms from the drug mixture produced complex, overlapping profiles, and chemometrics methods were applied for calibration modeling. It was shown that satisfactory quantitative results were obtained with the use of the MVC1package of chemometrics methods e.g the PLS1calibration model produced a relative prediction error (PRET) of7.0%and an average recovery of97.6%. The above AuNP/GCE was successfully employed for the simultaneous analysis of RAC, SAL and CLB in pork meat, liver and pig feed samples.2. The electrochemical behaviors of three antioxidants:butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and butylated hydroquinone (TBHQ) at a gold nanoparticles modified glassy carbon electrode (AuNPs/GCE) were investigated. The modified electrode was characterized by scanning electron microscope (SEM). The experimental results indicated that the modified electrode exhibited an excellent electrocatalytic activity towards the redox reactions of BHA, BHT and TBHQ, testified by the increased redox peak currents and shifted potentials, and in addition, the oxidation products of BHA and TBHQ were found to be the same. The experimental conditions were optimized and the oxidation peaks of BHA and BHT were clearly separated. Based on this, an electrochemical method was proposed to simultaneously determine the BHA, BHT and TBHQ in mixtures by first derivative voltammetry, with linear concentration ranges of0.10-1.50μg mLL1,0.20～2.20μg mL-1and0.20～2.80jig mL-1, and detection limits of0.039,0.080and0.079μg mL-1, for BHA, BHT and TBHQ, respectively. The proposed method was successfully used for the analysis of the three analytes in edible oil samples.3. A novel modified electrode was constructed by the electro-polymerization of7-[(2,4-dihydroxy-5-carboxybenzene)azo]-8-hydroxyquinoline-5-sulfonic acid (DHCBAQS) at a graphene-nafion modified glassy carbon electrode (GCE). The construction process was performed stepwise and at each step the electrochemical characteristics were investigated particularly with respect to the oxidation of the three noxious analytes,2-nitroaniline (2-NA),3-nitroaniline (3-NA),4-nitroaniline (4-NA); the electrode treated with the fluorescence reagent DHCBAQS perfomed best. At this electrode, the differential pulse voltammetry peak currents of the three isomers-2-NA,3-NA and4-NA increased linearly with their concentrations in the range of0.05～0.55μg mL-1,0.05～0.60μg mL-1and0.05～0.60μg mL-1, respectively, and their corresponding limits of detection (LODs) were0.025,0.021and0.019μg mL-1. Furthermore, satisfactory results were obtained when this electrode was applied for the simultaneous quantitative analysis of the nitroaniline isomer mixtures by Principal component regression (PCR) and Partial least squares (PLS) as calibration methods (relative prediction error (PRET)-9.04%and9.23%) and average recoveries (101.0%and101.7%), respectively. The above novel poly-DHCBAQS/graphene-nafion/GCE was successfully employed for the simultaneous analysis of the three noxious nitroaniline isomers in water and sewage samples.4. A new modified electrode was constructed by the electro-polymerization of4,5-dihydroxy-3-[(2-hydroxy-5-sulfophenyl)azo]-2,7-naphthalenedisulfonic acid trisodium salt (acid chrome blue K (ACBK)) at a graphene-nafion modified glassy carbon electrode (GCE). The electrode was investigated by the electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and atomic force microscope (AFM) techniques, and the results were interpreted and compared at each stage of the electrode construction. At this modified electrode, the linear sweep voltammetry peak currents of the eight β-agonists (clenbuterol, terbutaline. ractopamine, salbutamol, dopamine, dobutamine, adrenaline and isoprenaline) increased linearly with their concentrations in the range of1.0-36.0ng mL-1, respectively, and their corresponding limits of detection (LODs) were0.58-1.46ng mL-1. This electrode showed satisfactory reproducibility and stability, and was used successfully for the quantitative analysis of clenbuterol in pork samples.5. A new modified electrode was constructed by the electro-deposition of the mixture of CuSO4and HAuCl4at a glassy carbon electrode (GCE). The eugenol was electrocatalytically oxidized at the Cu@AuNP/GCE, which enhanced the oxidation peak current and influenced the shift of the oxidation potentials to lower values in comparison with the analysis involving only the GCE. In order to confirm the electrochemical reaction mechanism for o-methoxy phenol, the electrochemical behavior for catechol, guaiacol and vanillin were studied. Based on this, the electrochemical reaction mechanism for o-methoxy phenols was inferred. At this modified electrode, the linear sweep voltammetry peak current of eugenol increased linearly with its concentration in the range of0.05-0.80μg mL-1, and its corresponding limit of detection (LOD) were0.042μg mL-1. Moreover, The above Cu@AuNP/GCE was successfully employed for the analysis of eugenol in food samples. |
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