| This thesis is aimed at environmental contaminations detection, mainly heavy metal ions in surface water and disinfection by-products (DBPs) in drinking water. The two categories of contaminations have different properties so that two correspondent methods were developed:one is based on fluorescent molecular sensors in a microfabricated device, the other one is based on conductive detection.In the first part, two fluorescent molecular sensors and several microfluidic devices were developed and applied for heavy metal ions detection in surface water. Further more, some improvements of the performance of microfluidic chips were made.A microfabricated device has been designed and fabricated for selective detection of cadmium ions in water. This method is based on a fluorescent molecular sensor for cadmium sensing in microfluidic chip. Rhod-5N consists of BAPTA moiety and a rhodamine fluorophore. The principle of this probe is photoinduced electron transfer occurring from one of the aromatic amine groups of BAPTA moiety to the rhodamine fluorophore in1:1complex. To eliminate the interference of lead, a solid phase extraction (SPE) preconcentration process was used to separate cadmium and lead. Then the sensor and analyte solutions were introduced into the microchannel and excited by a525nm UV LED. The fluorescence signals were collected and the calibration curve ranges from0to2μM (Rhod-5N1μM), and the limit of detection is4nM (0.45μg L-1).A new microchip made of PMMA was fabricated by femtosecond laser ablation and tested for Cd2+sensing based on a fluorescent molecular sensor Rhod-5N. The results were compared with that in cuvette and in PDMS-based microchip. Unfortunately, Rhod-5N molecules adsorbed on PMMA polymers and the adsorption affects the response of fluorescence detection, and the limit of detection is much lower than in PDMS-glass chip.A water soluble fluorescent sensor (DPPS-PEG) was used for Hg2+sensing, which is a diphenylphosphanomethane (DPPE) derivative with phosphane sulfide, and a poly(ethylene oxide)(PEG) group introduced to increase the water solubility. The principle of this fluorescent sensor is Hg2+interacted with sulfur atom of phosphane sulfide in1:1or1:2complex. The detection limit obtained in cuvette is3.8nM. Then a long microchip based on PDMS and glass was fabricated for mercury ions detection. The reactants were prepared in organic-aquous solution (CH3CN/H2O80:20at pH4.0), and2～3×10-4Triton X100was added to obtain stable fluorescence signals. The detection limit is about10nM (2.0μg L-1).In PDMS-based microfluidic system, air bubbles always occur and affect the fluorescence detection, so some improvements were developed to solve this problem. Three strategies were studied for trapping and debubbling of air bubbles, including portable bubble trap fabrication, hydrophilic PDMS surface treatment and phase-guide in microchip design. The bubble trap is based on the principle of buoyant force so that liquid and air can be separated before introduced into the micro-channel. The hydrophilic treatments were realized by two ways, O2plasma treatment (simple and convenient, but unstable) or PEG-coating on PDMS surface (effective and stable). The drawback is that fluorescent molecules are adsorbed on PEG grafted PDMS surface. Phase-guide was designed and fabricated in the detection chamber, and enable the control of priming. Air bubbles emptied the chamber and the overflow filling the chamber along the phase-guide wall. In general, the work is helpful for air bubbles prevention, separation and elimination.A novel method for sensitive determination of five priority haloacetic acids (HAAs) in water systems has been developed based on electromembrane extraction (EME) prior to capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D). The target HAAs were extracted into the supported liquid membrane (using a polypropylene membrane supporting1-octanol), and then back-extracted into few microliters of an acceptor solution. The extracted solution was directly analyzed by CE-C4D without derivatization. Several factors that affect separation, detection and extraction efficiency were investigated. Under the optimum conditions, five HAAs (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid) could be well separated from other components coexisting in water samples within23min, exhibiting a linear calibration over three orders of magnitude (r>0.999); the obtained enrichment factors (EFs) at430-671were obtained in a30min of extraction, and the limits of detection were in the range of0.165-0.609μg/L with relative standard deviation between1.17%and7.08%. This approach offers an attractive alternative to the official proposed method, which requires complex sample preparation and derivatization prior to analysis by gas chromatography. |
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