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Selenium is widely distributed in nature in relatively small concentrations in rocks, plants, coal and other fossil fuels. Selenium compounds are extensively used in paints, dyes, glass, electricals, rubber and insecticides, and in many other industries. 1 The determination of selenium is of considerable interest because of its contrasting biological effects; selenium is a toxic element as well as a trace element for animals and humans.2 Its efficiency causes pulmonary edema, abdominal pain, jaundice, chronic gastrointestinal diseases, hair loss and fatigue in humans, 3 and its deficiency causes Keshan and Kaschin beck diseases in humans, which have been frequently reported in China. 4 It also plays a major role in the life cycle of plants (Cruciferae family) which absorb organoselenium compounds accumulated in the soils of semiarid areas, and may poison livestock that graze on them. Selenium enters into natural water through seepage from seleniferrous soil and industrial waste. Water drained from such soil may cause severe environmental pollution and wildlife toxicity.2 Selenium is also reported to be present in cigarette paper, tobacco, 5 and various cosmetic samples. 6 Because of its significance, several analytical techniques have been reported concerning the determination of selenium. 7-10Many spectrophotometric methods for the determination of selenium have been reported with some chromogenic reagents, such as 3,3-diaminobenzidine, 11 dithiozone, 12 8-hydroxyquinoline, 1-naphthylamine-7-sulfonic acid 16 and Leuco Crystal Violet. 17 Of these reagents, some have been reported to be carcinogenic, while few others are less selective; the latter reagent system required heating and 25 min for full color development. There is thus a need to develop an entirely new method, which would overcome the existing inadequacies in the determination of trace amounts of selenium.In the present investigation, a facile, sensitive and selective method has been reported for the determination of selenium with a new reagent Variamine Blue (VB), based on the liberation of iodine by the reaction of selenium with potassium iodide in an acidic medium and a subsequent oxidation of VB by the liberated iodine to form a violet-colored species. The developed method has been successfully employed for the determination of selenium in water, soil, plant materials, human hair, cosmetic and pharmaceutical preparations. Experimental ApparatusJasco (Model UVIDEC-610) and Elico (Model CL-27) spectrophotometers with 1 cm matched quartz cells were used for all absorbance measurements. ReagentsAll of the chemicals used were of analytical-reagent grade, and distilled water was used throughout the study. Standard selenium(IV) solution (1 mg/ml).Prepared by dissolving 0.219 g of Na2SeO3 in 100 ml water. A working standard solution was prepared by a suitable dilution of the standard solution. Variamine Blue (VB), (0.05%). Prepared by dissolving 50 mg of Variamine Blue (E. Merck, Germany) in 25 ml methanol and made up to 100 ml with distilled water, and s...

A detailed investigation of photocatalytic degradation of Acid Yellow 36 (AY36) has been carried out in aqueous heterogeneous medium containing ZnO as photocatalyst in a batch reactor. The effects of some parameters such as pH, catalyst loading, and ethanol concentration were examined. Solutions with initial concentration of 50 mg L−1 of dye, within the range of typical concentration in textile wastewaters, were treated at natural pH of 6.93 and catalyst concentration of 1 g L−1 after 180 min irradiation. Investigations on the active species indicated that hydroxyl radicals play the major role in the process. Experiments showed that the most efficient pH on the removal of the dye with photocatalytic degradation process was 8; however, acidic pH was favored for the dark surface adsorption. Electrical energy consumption per order of magnitude for photocatalytic degradation of AY36 has been also determined.

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