| Deltamethrin(DM) pesticides have the advantages of high efficiency, low toxicity, broad-spectrum and so on. DM had been widely used in grains, fruits and vegetables, tea and other agricultural products for prevention and cure of diseases and pests. Researches on rapid detection techniques can provide technical support for monitoring the DM residues in agricultural products, give guidance for its useage and ensure food quality and safety.In this study, a kind of electrochemical sensor based on multi-walled carbon nanotubes(MWCNTs) modified glassy carbon electrode(GCE) was developed for the rapid detection of DM, and had been successfully used for determination of agri-production. To further enhance the sensitivity and specificity of the electrochemical detection for DM. The molecular imprinting pre-assembled system was studied by UV spectroscopy and computer simulation techniques. It can provide theoretical guidance for the preparation of molecularly imprinted membrane for DM. The main conclusions are as follows: 1. Research on MWCNTs modified GCE for DM determination(1) The key points of preparation process of MWCNT modified GCE were optimized for the better sensitivity. The most optimal preparation conditions are as follws: the mass concentration of dispersant SDS of 0.5%, dispensing volume of 5 μL and drying temperature of 25℃.(2) Electrochemical measurement conditions for DM were optimized and 0.1 M Na OH in 50% aqueous alcohol as background electrolyte, the peak shape of DM was sharp with the lower peak potential and the higher peak current. The most optimal parameters of DPV are as follws: Accumulating time of 60 s, incr E of 0.016 V, pulse amplitude of 0.0125 V, pulse width is 0.1 s and pulse period of 0.5 s, reduction curve of DM show the highest I and good sensitivity.(3) The methodology of electrochemical sensor based on MWCNTs/GCE was verified. The relationship between the response current of the reduction of DM and concentrations showed two linear regression equations at-0.920 V: I1(μA)= 1.5484+59.7360C(mg/kg)(R2=0.9863, 0.005~0.100mg/kg) and I2=7.8560+0.0877C(mg/kg)(R2=0.9988, 0.100~100.000 mg/kg), and a detection limit of 0.001 mg/kg. The accuracy was tested and the recoveries were arranged from 96.1%-103.5% for the spiked tangerine and tea samples by 0.5 times, 1.0 times, 1.5 times of DM. The repeatability was evaluated by using the same MWCNTs/GCE for 8 successive measurements and 5 MWCNTs/GCEs prepared at the same conditions for measurement of DM(50mg/kg), the RSD was 2.23% and 3.61% respectively. The stability of the developed sensor was investigated by measuring the current shift at different storage times. The results indicated that the current response could retain 85.90% of its initial current response to DM after storage for 5 days at 4℃. MWCNT/GCE showed good anti-interference to the distractors, the peak current values with or without Interferences showed no significant differences(p = 0.05).(4) Real samples such as tangerine and tea were detected by our method and GC methods. The result showed no significant differences.in these two methods. And the machine detection time of MWCNTs/GCE electrochemical is about 2min while the detection time of GC method is about 1 hour. And electrochemical detection didn’t require cartridge Florisil during pretreatment process. The cost of electrochemical method is much cheaper than GC method. The electrochemical sensor based on MWCNTs/GCE can detect deltamethrin rapidly and economily. 2. Study on preassembled system of DM molecular imprinting by UV method.(1) The ultraviolet spectrum of preassembled system of DM molecular imprinting was studied: DM had hydrogen bonding interactions with three kinds of monomers, and hydrogen bonds let absorption of DM get red-shifted. And the DHB showed the strongest impact on the preassembled system, OPD followed and OAP was the worst.(2) By differential ultraviolet spectrum, it showed that DM was difficult to form stable complex with OAP, a molecule DM could form two relatively stable complexes with one or two molecules DHB, and the most complex type was DM-2DHB; in addition, a DM with one or two molecules could form DM-OPD or DM-2OPD. However, the binding constant k between DM-DHB was much larger than DM-OPD, which indicated that DM prefer to forming stable complex with DHB. 3. Study on preassembled system of DM molecular imprinting by Molecular simulation(1) The combine energy between DM and functional monomer was calculated: the order of energy reaction was DHB>OAP> OPD. Combining energy between DM and DHB was maximum, which indicated that the compound was the most stable. The stability of DM-OPD was the worst. The complex was more stable, the selective synthesis efficiency of molecular imprinting was higher. It could be expected that imprinted efficiency of DHB and DM synthesized MIM was the best.(2) The steric configuration, bonding situation and combine energy of template molecule and functional monomer under different ratios were simulation calculated: when the template molecules and three kinds of functional monomer in ratios of 1:3, the combine energy was the largest, and there were three hydrogen bonds, the steric configuration was the most stable.(3) The solvation energy between DM and three monomers complexes in three kinds of solvents were calculated: the effect of solvents on complex was ranged as: acetonitrile> acetone> n-hexane, which showed that n-hexane was most suitable solvent for synthesis of MIM. |
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