Determination Trace Of Mercury(II) And Nitrite By Fluorescent And Colorimetric Sensors And Phthalate Esters In Powdered Milk By Ultra Performance Liquid Chromatography

In this thesis, the determination of a trace of mercury（II） and nitrite by fluorescentand colorimetric gold nanoparticles sensors was reported with enhanced sensitivity.Thirteen phthalate esters in powdered milk were determinated simultaneously by ultraperformance liquid chromatography. Details are listed below.1. Fluorescent sensing of mercury（II） based on formation of catalytic goldnanoparticlesThe oxidization of o-phenylenediamine （OPDA） by dissolved oxygen to produce2,3-diaminophenazine（DAP）, which is a product of strong fluorescence. But rate of thisreaction is very slow without catalyst. The coexistence of Hg²⁺and polyethylene glycolstabilized gold nanoparticles （AuNPs） forms Hg-Au alloy on the surface of AuNPs,which accelerates the oxidization of OPDA by dissolved oxygen. A fluorescence assayfor the highly sensitive and selective detection of Hg²⁺was proposed. The fluorescenceintensity is in a linear correation with the concentration of Hg²⁺in the ranges of5.0-100nmol/L. The limit of detection is2nmol/L, the recovery of spiked5-60nmol/L of Hg²⁺in a standard addition method were in the ranged of93to105%.This method avoidesthe addition of extra oxidant, making the sensing system simpler.20-fold of Ca²⁺, Mg²⁺,Zn²⁺, Cr3+, Pb²⁺, Cr（VI）, Mn²⁺, Cd²⁺, Fe3+, Al3+, Ni²⁺,10-fold Fe²⁺, Co²⁺,5-fold Cu²⁺and the same concentration of Ag+caused almost no fluorescence signal, indicating thatthe sensor displayed excellent selectivity toward Hg²⁺. 2. Positively-charged AuNPs-based nitrite colorimetric sensorA positively-charged AuNPs-based nitrite colorimetric sensor was demonstrated.4-Aminothiophenol functioned nanoparticles in the acidic solution with ethanol wereaggregated by heating at80°C. In the presence of nitrite ions, the deamination reactionof4-aminothiophenol takes place, which led to dispersion of AuNPs and a colorimetricresponse that was quantitatively correlated to the concentration of nitrite ions. Thissimple assay was highly sensitive and a novel application of a positively-chargedAuNPs-based nanoprobe for nitrite detection.Under optimum experimental conditions,the detection limit for nitrite by nake eyes is below1μmol/L.3. Simultaneous determination of thirteen phthalate esters in powdered milk forinfants and young children by ultra performance liquid chromatography-photo-diode arrayA method was developed for the simultaneous determination of thirteen phthalateesters in powdered formulas for infants and young children by ultra performance liquidchromatography-photo-diode array. Samples were extracted with methanol saturated byn-hexane in an ultrasonic field, cleaned up by refrigerated centrifugation, and then thesupernatant was cleaned by0.2μmol/L hydrophobic membranes.The target analyteswere separated on an HSST3column with gradient elution using acetonitrile and wateras mobile phases. The identification and quantification were achieved by usingphoto-diode array detector. Linear ranges of thirteen phthalate esters were from0.5to50mg/L with the correlation coefficients （r） above0.99. Limits of detection were in therange of0.05-0.4mg/L. The average recoveries of the method were from92%to102%.The relative standard deviations were less than10%.The method is simple,highlysensitive,rapid,broad test range and suitable for the simultaneous determination ofthirteen phthalate esters in powdered formulas for infants and young children..4. Acceleration color removal by foreign particles in flocculation usingpoly（epicholorohydrin-diamine）Color removal of a model dye wastewater of weak acid orange GS was tested by a chemical flocculation process using poly（epicholorohydrin-diamine）. Under theconditions used, the color removal efficiency in this system was low because the lowsedimentation rate of the fine flocs. The sedimentation was accelerated and colorremoval was enhanced by adding micro-amount of foreign particles such ascarbon-containing residue, kaolin, titanium dioxide or silicon dioxide nanoparticles. Itwas shown that these foreign particles have favorable effect on the nucleation of theflocs. The turbidity removal process is helpful to color removal during this flocculation.