Novel UV-photochemical Reduction Of Te And As And Its Analytical Application

The analysis of trace or ultra-trace elements in environmental samples has positive impact on environmental science and environmental geochemistry.However,the lack of accurate,reliable and sensitive trace or ultra-trace elemental analysis methods in current environmental science and environmental geochemistry often poses obstacles to the in-depth study of related research.Therefore,it is of great significance to develop novel,efficient and simple elemental analysis methods,which can be applied to the analysis of trace or ultra-trace elements in the environment.UV-photochemical vapor generation?UV-PVG?is an emerging sample introduction technology,utilizing free radicals as reductants,which is generated by photo-decomposition of low molecular weight organic compounds?LMWAs?,can transform a target analyte into itis corresponding vapor species,which can be detected by atomic spectrum.UV-PVG not only has the advantages of high sampling efficiency,low matrix interference,but also the advantages of simple operation,environmental friendliness,and cost-effectiveness.Tellurium?Te?is regarded as a toxic element for humans,which can affect various organs.Te receives great attention due to its optoelectronic and thermal properties,which has been widely used in industrial applications,new materials development and fluorescent probes production.Thus,the potential risks of humans exposing to tellurium is increasing,which may poses risks to human health.Arsenic?As?is a toxic and carcinogenic element,which can cause cancer in human skin,lungs,liver,and bladder.In 1993,the World Health Organization?WHO?stipulated that the content of As in drinking water should not exceed 10?g L^-1.Thus,accurate analysis of Te and inorganic As in environmental samples is essential.In this research work,novel photochemical vapor generation systems using transition metal ions or photocatalysts as sensitizers will be developed for the determination of tellurium and arsenic species in environmental samples.Specific work includes the following two aspects:?1?Due to unique feature of Te to form volatile species,photochemical vapor generation?UV-PVG?is emerging as a promising analytical tools for its determination.UV-PVG utilizes free radicals as reductants,which is generated by photo-decomposition of low molecular weight organic compounds?LMWAs?.UV-PVG can efficiently separate analyte from troublesome sample matrix and provide a very simple and green procedure for chemical vapor generation.However,the low UV-PVG generation efficiency of Te often limits its wide application in environmental samples with trace Te levels.Transition metal ions can greatly increase the efficiency of light-induced vapor generation.In addition,the researchers found that photocatalyst—nano-TiO₂ can also effectively increase the vapor generation efficiency of Se?VI?.Under ultraviolet radiation,nano-TiO₂ can generate electrons,which can reduce Se?VI?into its vapor form.By irradiating nano-TiO₂ with short-wavelength UV light?254 nm and185 nm?,its photocatalytic capacity can be effectively improved,thus the photolysis efficiency of volatile organic compounds can be increased.Herein,enlightened by the above-mentioned phenomena,a highly sensitive Te UV-PVG assay was developed after the synergistic enhancement of transitional metal ions and nano-TiO₂.The UV-PVG was carried out under short-wavelength UV irradiation?254 nm and 185 nm?,in the presence of ferric ion and photocatalytic nano-TiO₂.The ferric ion enhances the signal intensity of Te?IV?,while nano-TiO₂ can further enhance the signal intensity and photoreduce Te?VI?to Te?IV?in the presence of ferric ion.The risks of analyte loss and sample contamination during the traditional prereduction procedure are eliminated for Te determination.The main parameters potentially influencing UV-PVG of Te and its transport efficiency to ICPMS were optimized,including the concentration of ferric species,nano-TiO₂ and LMWAs,irradiation time and Ar carrier gas flow rate.The accuracy of the proposed method is validated by the analysis of three surface waters and two sediment samples.To our best knowledge,this is the first report of synergistic enhancement of transitional metal ions and nano-TiO₂ in UV-PVG,which possesses potential for highly sensitive determination of vapor-forming elements.?2?Transition metal ions have the potential to greatly enhance the efficiency of UV-PVG.However in present there are few studies focusing on the investigation of the effectiveness of transition metal ions as sensitizers to improve the efficiency of UV-PVG systems,thus in order to further understand the application of transition metal ions in the UV-PVG system,more in-depth studies are needed.Thus,in this study a novel photochemical vapor generation system of As based on cobalt ion sensitized was developed.In this UV-PVG system,30?g mL^-1 Co?II?can effectively increase the vapor generation efficiency of As,which was enhanced approximately 72 fold for As in the presence of Co?II?,and effectively improve of the reaction kinetics of As.In this UV-PVG system the generation efficiency of volatile As species was highly depended on pH of sample solution,and the best reduction efficiency of As could be achieved when pH was 3.Under the optimum condition,a LOD of 4 ng L^-1 could be achieved.The proposed method is highly sensitive and precise,which has potential to determinate As in environmental samples.