| Diazepam, one of the psychotropic drugs, is commonly used as minor tranquillizer, hypnotics, muscle relaxant and as anticonvulsant. Improper use of diazepam leads to central nervous system impression and respiratory depression. Furthermore, the drug dependence and addiction can be caused by frequent use of diazepam. Benzodiazepines, including diazepam, are prohibited in the edible animal tissue. However, there is still possibility that these agents were illegally used for increasing feed conversion and the economic benefit, leading to the potential hazard to the environment and public health. The practical detecting methods are key points for controlling the abuse of psychotropic drugs. Up to now, the main approaches for the detection of diazepam residue include immunoassay, chromatography and chromatography coupled with mass spectrum. However, the disadvantages of these methods were represented by complex analyzing processes, long time for pretreatment of biological samples and expensive instrumentation. These techniques hardly meet the requirements of the rapid on-site screening for large amounts of real samples. Electrochemical sensor, which shows the advantages of short assay time, preferable accuracy and low cost, represents an important trend in the detection of diazepam residue.The techniques based on molecularly imprinted technique involve the preparation of polymers with selective recognition sites for specific molecule. It is of great significance if novel electrochemical sensors are fabricated based on the molecularly imprinted polymers employed as recognition unit for the detection of drug residues. Based on the theory of molecularly imprinted polymers and the techniques of electrochemical sensor, new type of materials for the construction of sensing unit and electrode were selected to exert the advantages of the specificity, practicability and preordainment by molecularly imprinted polymers. In this study, two types of electrochemical sensors for determining diazepam in animal products were established, showing the advantages of short assay time, low cost, straight-forward, convenient and satisfactory efficiency. The main work of this study is shown as follows:1. The study of superficial and absorption characterizations of diazepam molecularly imprinted polymers: Molecularly imprinted polymers were synthesized using diazepam as the template by thermal polymerization method. The binding mechanism and recognition characteristics of the molecularly imprinted polymers were studied by ultraviolet spectra and infrared spectra. The results showed that template molecules and functional monomers had formed 1:2 hydrogen bonding complexes. The adsorption characteristics of the polymers toward the target molecules in the adsorption process were in coincidence with Freundlich isotherm equation and adsorption rate with Langergen quasi-second order kinetics equation. The molecularly imprinted polymers exhibited high adsorption capacity and specificity, which can be used as sensing materials for electrochemical sensors. 2. Preparation of conductometric sensor for the detection of diazepam based on molecularly imprinted film:个Molecularly imprinted films were synthesized in situ using diazepam as the template on screen printed electrodes. A sensor based on molecularly imprinted films for the detection of diazepam was assembled by connection the electrode to a portable conductometer through an electrode slot. Standard calibration curve was established and the detection of diazepam in meat samples was performed on the sensor. The response of the conductometric sensor to the concentration of diazepam displayed a linear correlation over a range from 0.039 to 1.25 mg/L with a detection limit of 0.008 mg/L, the recoveries were 91%95% and the detection time was within 180 seconds based on meat samples. The sensing system exhibited satisfactory reproducibility and stability with the shelf life of above four months. In summary, this technique can be used as a quick, preferable sensitive and practical approach for the detection of diazepam on site.3. Preparation of amperometric sensor for the detection of diazepam based on molecularly imprinted film:个Molecularly imprinted film modified screen printed electrodes were prepared by electro-polymerization method based on cyclic voltammetry using o-phenylenediamine as the functional monomer and diazepam as the template. The detection of diazepam performed on an electrochemical working station using molecularly imprinted film modified screen printed electrode as the transducer. Potassium iodide was employed as a probe for indirect determination of diazepam on the amperometric sensor. The results indicated that a linear correlation of the sensor signal with diazepam concentration was shown over a range of 2×10-71×10-5 mol/L. The detection limit was 2.5×10-8 mol/L and the optimized accumulation time for detection of diazepam was 3 minutes. The advantages of this sensing system could be represented by short assay time, easy operation, favorable stability and reproducibility.
|
PDF Full Text Request