| The Cr(Ⅲ) and the Cr(Ⅵ) ions usually exist in simultaneously in nature.The different chromium speciation would produce different physiology function. The Cr(Ⅲ) cation is a kind of indispensable microelement to human body, which could participate in sugar and fat metabolism in organic body. But the chromium(Ⅵ) compound is just a generally accepted carcinogen, whose toxic was 100 times more than that of chromium(Ⅲ). The compound which includs chromium(Ⅵ) would damage the cardiovascular and hematopoietic function in animal bodies, cause the pathologic change of liver, kidney and lung, make the embryo malformation and so on. It also has strong irritation and high permeability to skin. Moreover, it has the embryonic development toxicity and the teratogenicity to the animals. Recently, with the rapid development of industries of leather, electroplating and metallurgy , which have relation with chromium(Ⅵ) compounds , the quantity of the chromium(Ⅵ) cation is increased rapidly in environment. Thus the work of determination of chromium(Ⅵ) cation becames a very important project in the fields of chemistry, environmental science, life science and physical medicine.Eelectric analysis, chemiluminescence method, atomic absorption spectrometry, atomic emission spectrometry, voltammetric and inductively coupled plasma mass sprctrometrci are general ananltical methods for the determination of chromium(Ⅵ). The disadvantages of these methods are operating complicatedly, consuming much time and needing more reagents and needing expensive apparatus, which have large limitation to the application and popularizing of these methods. The studies of new analytical spectrophotometric and florescence methods for the determination of trace amount of chromium(Ⅵ) cation were carried out in this work, which had the advantages of simple requiring and convenient operating and so on. The major contents of the paper were described as follows:Part one Catalytic Kinetic Spectrophotometric Method for the Determination of Trace Amounts of Chromium (Ⅵ) Cation with Methyl Orange as DeveloperTrace amounts of chromium(Ⅵ) cation were detemined by kinetic spectrophpotometry, which was based on its catalytic effect on the redox reaction between methyl orange and H2O2 in H2SO4 aqueous solution medium at 90℃. The determination signal difference (△A) between catalytic reaction and non-catalytic reaction was linear with the concentration of chromium(Ⅵ) in a certain range. The optimum conditions available had been found: The apparent activation energy was 25.73 KJ·mol-1 ; the linear range of determination was 0～72μg·L-1 and the detection limit was 4.74μg·mL-1. The interfering ions on iodide determination were also studied. The method was simple and selective and most ions were out of interfering. Compared with the standard method, it could be found that both of the methods were comparative.Part two Catalytic Kinetic Spectrometric Determination of Trace Chromium (Ⅵ) Cation Using Oxidation of Crystal Violet with H2O2A new catalytic kinetic-spectrohpotometric method for the determination of trace chromium (Ⅵ) has been proposed. It was based on the chromium (Ⅵ) cation which could catalyze the redox reaction between H2O2 and crystal viole in H2SO4 aqueous solution edium at 75℃. The absorbance difference (△A)between catalytic reaction and non-catalytic reaction was linear with the concentration of chromium (Ⅵ) in a certain range. On optimum conditions, calibration curve was linear in the range of 0-96μg/mL, with the detection limit as low as 6.91μg·mL-1 (regression coefficient was 0.9985).The regression equations was△A = 0.0033 + 0.1401C (μg/25mL). The method was simple and selective. It has been applied satisfactorily to the determination of chromium (Ⅵ) in wastewater samples.Part three Highly Sensitive Fluorescence Quenching Method for Determination of Trace Chromium(Ⅵ) Cation With Safranine TA new fluorescence quenching method based on oxidation reaction for the determination of trace chromium(Ⅵ) has been proposed. It was based on the principle as follows: in HCL aqueous solution medium, redox reactions occurred between chromium(Ⅵ) and safranine T, which has primary amino group . After the reaction, the fluorescent primary amino group disappeared and molecular electronicsπconjugate degrees reduced, which reduced the fluorescent efficiency of product molecules and the fluorescent strength of the whole system. The results show that the largest excitation wavelength of Tibetan T was at 559.0 nm and the largest emission wavelength was at 575.0 nm in the acid medium. It could be found that chromium(Ⅵ), whose content was 0 128μg L-1 within the framework of the system, had good linear relationship with fluorescence response. The detection limit was 2.5μg L-1 and the relative standard deviation was 1.2%. This method, which was sensitive, low-cost, simple, fast, etc., has been used in the determination of trace chromium (Ⅵ) cation in electroplating wastewater, industrial wastewater, water and the lake water. Compared with the standard method, it could gain satisfactory results.
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