| Hydroxylated polychlorinated biphenyls(OH-PCBs) are a class of typical second-generation persistent organic pollutants, which are produced in the environment by the oxidations of polychlorinated biphenyls(PCBs) through metabolic transformation in living organisms and abiotic reactions with hydroxyl radicals. OH-PCBs, as new environmental contaminants, are widely distributed in the world. It has been reported that OH-PCBs can be found not only in the blood and tissues of humans and wildlife, but also in the aquatic environments such as sediment and surface waters. The determination of OH-PCBs is of great importance from the ecotoxicological point of view since a number of OH-PCBs have been identified as endocrine disruptors. Consequently, several methods have been developed for detection of OH-PCBs. However, it should be noted that most of the applications of these methods developed so far are limited to measurements with biological samples such as blood and tissues. Very few methods have been reported for the determination of OH-PCBs in environmental water samples. Thus, the aim of this thesis is to develop the on-line and off-line systems for the detection of OH-PCBs in the environmental waters. In these systems, the solid-phase extraction(SPE) based on hydrophilic molecularly imprinted polymers(MIPs) as sorbents is used as an efficient way for sample separation and preconcentration. After preconcentration, OH-PCBs are determined by liquid chromatography coupled with tandem mass spectrometry(LC-MS/MS) and polymeric membrane ion-selective electrode, respectively. Combining with the flow analysis system which can be used to improve the sensor efficiency, a new on-line method for the rapid potentiometric determination of OH-PCBs in environmental waters is further developed. The contents of this thesis are shown as follows:1. Synthesis of hydrophilic MIP for OH-PCBsIn recent years, MIPs with excellent recognition abilities have been developed for preconcentration and determination of OH-PCBs in environmental samples. However, most of the MIPs developed for OH-PCBs are compatible with organic solvents, and fail to show specific template bindings in aqueous solutions since the strong nonspecific adsorption of OH-PCBs to the hydrophobic surface of MIPs usually occurs in aqueous media. This significantly limits their practical application in such areas as molecularly imprinted sorbent assays. In addition, owing to the large variety of structures and high toxicity, OH-PCBs cannot be employed as the template. Herein, we report the efficient synthesis of the hydrophilic MIP for OH-PCBs. The proposed MIP is synthesized by precipitation method using hydrophilic acrylamide as a functional monomer, trimethylolpropane trimethacrylate as a cross-linking agent and 4,4’-dihydroxybiphenyl as a dummy template. Experiments show that the uniform polymer spherical particles have a diameter of 2-3 μm.2. Preparation of molecularly imprinted SPE column for OH-PCBsThe proposed MIP based on the dummy template was utilized as an adsorbent in SPE for selective preconcentration of OH-PCBs. In order to obtain an optimal recovery of the target analyte in aqueous solution, the experimental parameters for SPE are optimized. A satisfactory recovery can be obtained by using 10 m L of hexane/Et OAc(1/1, v/v) as eluent, 50 mg of dosage, sample p H 11.0, 30 m L min-1 of sample flow rate and 10 m L min-1 of eluting flow rate.3. An off-line detection method based on molecularly imprinted SPE coupled with LC-MS/MS for OH-PCBs in environmental watersTraditionally, measurements of OH-PCBs can be done using gas chromatography-mass spectrometry(GC-MS) and LC-MS. For GC-based approaches, sample clean-up and derivatization procedures are always required, which may result in losses in sensitivity due to sample handling. Compared to GC-MS, LC-MS methods do not need derivatization of phenolic compounds and therefore are more promising for OH-PCBs detection. So far several papers have been reported for LC-MS-based measurements of OH-PCBs in blood matrix, but none for measurements in the aquatic environment. Herein, an off-line detection method based on SPE coupled with LC-MS/MS is developed to determine trace amounts of OH-PCBs in the aquatic environment. OH-PCBs can be detected in the linear concentration range of 0.05- 1.0 p M, with the detection limits ranging from 11 f M to 82 f M for 4’-OH-CB 9, 4’-OH-CB 30, 4’-OH-CB 61, 4’-OH-CB 106 and 4’-OH-CB 112, and the relative standard deviation(RSD %) was less than 8 %. The proposed system has been successfully applied to the determination of trace OH-PCBs in spiked water samples with recoveries in the range of 89- 109 %. These results indicate that the developed method can offer promising potential for the detection of trace-level OH-PCBs in real water samples.4. Fabrication of polymeric membrane ion-selective electrode(ISE) for OH-PCBs: Compared with the chromatography, chemical sensors have shown to be promising for environmental trace analysis due to their intrinsic advantages including excellent selectivity, low cost and ease of use. A few chemical sensors have been prepared for the detection of OH-PCBs using appropriate signal transductions such as amperometry and spectroscopy. However, these methods suffer from several problems such as low sensitivity and tedious detection process. Potentiometric sensors are generic and highly successful approaches to chemical sensing. With attractive features of portability, low cost and ease of miniaturization and integration, polymeric membrane ISEs have been widely used in environmental monitoring. Despite their great advantages, none has been reported for the detection of OH-PCBs. In this work, a polymeric membrane ISE for the determination of OH-PCBs is described. By optimizing the experimental conditions such as membrane composition, sample p H and rotation speed, a low detection limit is obtained. The proposed electrode response ranges from 6.3×10-9 to 6.0×10-7 mol L-1, and the lowest detection limit is 1.5×10-9 mol L-1 for 4’-OH-CB 106. These results suggest that the proposed sensor can be used for sensitive detection of OH-PCBs.5. Development of prototype sensing system for OH-PCBs in environmental watersThe sensitive and selective sensing systems for rapid and on-site monitoring of OH-PCBs have been developed based on the combination of flow analysis based on molecularly imprinted SPE and ISEs. This system integrating on-line filtration, enrichment and potentiometric detection can be used for on-site determination of OH-PCBs in environmental samples. The proposed system exhibits linear range in the range of 6.0×10-11 to 1.0×10-9 mol L-1 with a detection limit of 2.6×10-11 mol L-1 for 4’-OH-CB 106. The developed on-line sensor system has been successfully applied to determination of OH-PCBs in sea water samples with recoveries in the range of 82- 104 %. The study on sensor technology for on-site and rapid monitoring of OH-PCBs will provide important technical support for efficient environmental monitoring and evaluation of marine and coastal zone. Also, it can satisfy the urgent need of our country in environmental water monitoring. |
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