| The biological effects of an element are highly depend on its chemical form, and therefore comprehension of the bioavailability, assimilation, and excretion of the element is only possible through determination of the species present rather than determination of the total elemental concentration. Thus speciation analysis, which comprises the identification, quantification, and structural characterization of the species, is one of the key challenges of the environmental analytical chemistry.In this paper, the speciation of mercury, arsenic and selenium were studied using high performance liquid chromatography coupled with atomic spectrometry. The main work and conclusions listed as following:First, a method based on high performance liquid chromatography-UV-hydride generation on line coupled with atomic fluorescence spectrometry (HPLC-UV-AFS) for mercury speciation in seafood was proposed. Different extraction methods for methylmecury in fish and shellfish were also investigated. The samples were digested by 25% KOH in methanol, shaken for 10 hours, extracted by CH2Cl2, then back-extracted by 0.01mol L-1 Na2S2O3 and then measured. Under the optimized conditions, the relative deviations for the determination of methyl-, inorganic and ethylmercury are 4.4%, 3.9% and 4.3%, the detection limits for methyl-, inorganic and ethylmercury are 0.069, 0.15 and 0.046ng mL-1. The recoveries for methylmercury in fish and shellfish are 96±5% and 95±5%.Second, a novel separation method for mercury species using cation liquid chromatography on line coupled with atomic fluorescence spectrometry was proposed. The mercury species (inorganic mercury, methylmercury and ethylmercury) were baseline separated within 15 min by using cation-exchange chromatography on the PRP X-200 column with a mobile of 20mmol L-1 pyridine, 1% L-cysteine and 3% acetontrile. The linear range for inorganic, methyl-and ethylmercury were from 0-500ng mL-1, and the detection limits for inorganic, methyl-and ethylmercury were 0.12, 0.089 and 0.076ng mL-1. Further, a simple method for methylmercury determination using atomic fluorescence spectrometry without UV cracker was proposed. The two methods were validated by certified reference material DORM-2, results showd goog agreement with the certified values.Third, a method based on high performance liquid chromatography-hydride generation on line coupled with atomic fluorescence spectrometry (HPLC-HG-AFS) for arsenite (AsⅢ), dimethylarsinic acid (DMAⅤ), monomethylarsonic acid (MMAⅤ) and arsenate (AsⅤ) in seafood was proposed. The sample was extracted by a methanol-water mixture (1:1, v/v), condensed and then cleaned up by Oasis HLB cartridges. The extracts were separated by anion-exchange chromatography on the PRP X-100 column with an aqueous solution of KH2PO4 at pH 6.0 as mobile phase. The results demonstrated that the linear range for AsⅢ, DMAⅤ, MMAⅤand AsⅤwere from 0 to l000ng mL-1 and the correlation coefficient was exceeded 0.99. The average spiked recoveries were ranged from 89.6 to 95.3%. Under the optimized conditions, the detection limits for AsⅢ, DMAⅤ, MMAⅤand AsⅤwere 1.4, 2.5, 2.0 and 4.2 ng mL-1 respectively. The proposed method was simple, sensitive, and reliable for the determination of arsenic speciation in seafood.Further, a method based on HPLC-ICP-MS for selenite and selenate was proposed. The on line coupling system has been applied in wine and drinking water after preconcentration by A-alumnia cartridge.In the last, thiourea was novelly developed as a reduction reagent under the titanium dioxide catalyzed for on-line reduction of selenate before hydride generation. Different parameters affecting the signal of selenium species such as the concentration of thiourea, the concentration of hydrochloride acid, the concentration of KBH4, the concentration of suspension TiO2 and flow rate of carries gas were discussed. Under the optimized conditions, the limits of detection of selenite and selenate were 2.38 and 3.39 ng mL-1 respectively.
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