Study On The New Methods For Hypochlorite, Fluoride And Uranyl Determination By Spectrofluorimetry

This paper mainly investigates the specific interaction of ferrocyanide-thiamine and hypochlorite ions, calcium(Ⅱ)-cucurbit[7]uril-thioflavin T and fluoride anions, and Triton X-100-curcumin-uranyl ion systems. The absorption and fluorescent spectra of the above three luminescent system is systematically studied. As a consequence, new and simple spectrofluorimetric assays are proposed and validated for the qualitative and quantitative determination of hypochlorite, fluoride and uranyl ions in different real samples. The research contents are described as follows:1. Enhanced spectrofluorimetric determination of hypochlorite based on the catalytic oxidation of thiamine to thiochrome in the presence of trace ferrocyanideAn enhanced spectrofluorimetric method for highly selective and sensitive determination of nmol L-1 levels of hypochlorite ions in tap water and some disfectants samples has been performed. In 0.2 mol L-1 NaOH aqueous solution, potassium hexacyanoferrate was specifically oxidized by sodium hypochlorite to form potassium ferrocyanide, which further reacted with non-fluorescent thiamine hydrochloride, resulting in the formation of blue fluorescent thiochrome. Notably, the fluorescence intensity was positively correlated with the concentration of sodium hypochlorite over the concentration ranges of 0.02-12.5 × 10-6 mol L-1. The detection limit was 6.1 × 10-9 mol L-1, which was lower than most of the recently published methods. The experimental conditions were optimized and effects of potentially interfering substances were evaluated and the results suggested an excellent priority on account of a certain amount of other anions, including ClO3-, BrO3-, IO3-, Cr2O72- and other acid radicals, would not interfere with the measurement. In addition, the sensing mechanism was confirmed by contrast experiment using ferricyanide as oxidants.2. Calcium(II)-stimulus-responsive cucurbit[7]uril-thioflavin T supramolecular nanocapsule for the determination of fluoride and logic gate operationIn pH 7.0 HEPES buffer solution, thioflavin T would react with macrocyclic cavity compound cucurbit[7]uril to form host-guest supramolecular complex. The molar ratio of thioflavin T and cucurbit[7]uril (in this case) is 1:2. This stoichiometrically combinated supramolecular complex exhibits intensive fluorescence emission in virtue of the inclusion-induced enhancement of molecular rigidity. However, the brilliant green fluorescence of cucurbit[7]uril-thioflavin T superamolecular complex can be selectively quenched by Ca(II) ions, in pace with the formaton of a capsule-like molecular assemblies. The as-formed supramolecular capsule shows excellent selectivity for fluoride anions because of calcium ion can selectively bind to fluoride ions to give insoluble calcium fluoride (CaF2) crystals, and thus the strong fluorescence of this luminescence sensing system can be effectively released. The maximum emission wavelength locates at 490 nm. The enhancements of fluorescence intensity shows a linear correlation of the concentration of fluoride ions in a certain varing range (10.4～5000 ×10-6 mol L-1), with a limit of detection of 3.1×10-6 mol L-1, which is 68 times lower than the maximum contamination concentration defined by the U.S. Environmental Protection Agency. Notably, this luminescent sensing system is unresponsive to other coexisting anions, including halides (Cl-, Br-, I-), pseudohalides (CN-, N3-, SCN-); the bisanionic species (CO32-(existed as HCO3- at pH 7.4), SO42-HPO4-) give weak or negligible response. In addition, the proposed fluorimetric assay has been successfully applied to monitor fluoride ions content in five dental products and several tap water samples with agreeable results. The individuality of this luminescent sensing system has also been employed to develop molecular memories.3. Selective Uranyl ions Determination by Spectrophotometry and Fluorescence Quenching Using Triton X-100 Micelles-capped CurcuminUnder pH 4.0 HAc-NaAc buffer medium, curcumin alone possesses extraordinary weak fluorescence emission. Nevertheless, the introduction of Triton X-100 micelles can largely enhance the fluorescence intensity of curcumin molecule. Uranyl ions can interact with micelles-capped curcumin compounds, along with the slight red shift of curcumin fluorescence (about 1-7 nm), and a clear decreament of absorbance (424 nm) and fluorescence (507) intensities. The absorbance (△A,424 nm) and fluorescence (△F, 507 nm) decrements are positively correlated to the amount of uranyl ions in the range of 6.0×10-6～1.4×10-5 mol L-1 and 3.7×10-6～1.4×10-5 mol L-1, respectively. The detection limit of spectrophotometric method is calculated to be 6.0×10-6 mol L-1. And detection limit of fluorescence quenching methods is 3.7×10-6 mol L-1, which is nearly 9000 times lower than the maximum allowable level in drinking water proposed by World Health Organization. Good selectivity is achieved because of a majority of co-existing substances (such as Ce4+, La3+, Th4+, etc.) do not affect the detection. The content of uranyl ions in tap water samples was determined by the proposed method with satisfactory results.