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The kinetics of photo-oxidation of indigocarmine dye-5,5-indigosulfonate disodium (5,5-IDS)-in an acid medium has been studied to discover the effect of different parameters in the efficiency of the process. The experiments were conducted applying ultraviolet (UV)-polychromatic radiation to oxygen-saturated solutions. All kinetic experiments showed that the dye reaction order was zero, and its initial concentration did not influence the experimental rate constant. An increase in the rate was observed with an increasing UV radiation dose (D uv ) and/or the acidity. Temperatures-ranging from 290 K to 320 K-did not significantly affect the rate constant, indicating the photochemical activation of the oxidative process. 5-Isatinesulfonate sodium (5-IS) was identified as a photo-oxidation product. The effluent of the phototreatment had no color and contained no toxic products. Results showed that UV-induced oxidation of 5,5-IDS dye in an oxygensaturated aqueous medium, at room temperature, is an alternative treatment to conventional chemical oxidation for the decoloring of indigoid-dye wastewater from the textile industry.

Alkali nitrites and nitrates, along with sodium chloride have long been used in the curing of meat products to prevent bacterial spoilage and to enhance the flavor, color and texture of these food products. Much concern has been shown about the level of nitrite in food because the nitrite can react in the stomach, with dietary components, to form toxic and carcinogenic nitrosamines.1 Other danger that can occur after nitrite ingestion is that this ion in the blood stream converts oxyhemoglobin to metahemoglobin, thereby interfering with oxygen transport in the blood.2 For these reasons, the nitrite content in meat products have been regulated and the majority of the analytical methods recommended by the legislations of different countries to determine its content are based on the Saltzman modification of the classical Griess method. Unfortunately, this spectrophotometric method is time consuming, since a lengthy procedure is necessary to carry out in order to obtain a clear solution before measurement, due to the fine suspensions formed during the meat extraction.The usefulness of ion-selective electrodes is widely recognized today and their properties and characteristics make them very attractive analytical tools for food analysis. Potentiometric determination of nitrite in smoked fish 3 , and animal feed 4 have been carried out using a nitrogen-oxide gas sensing electrode, with previous conversion of nitrite ion to nitrous acid by addition of an acid buffer. The use of a nitrate-selective electrode for the determination of nitrite in meat products, with previous oxidation to nitrate by addition of potassium permanganate, has been proposed. 5Recently a nitrite-selective electrode has been commercialized, but successfully applications to food analysis have not been published. In this work the evaluation of the behavior of this electrode and its applicability to the determination of nitrite in different types of meat products is reported for the first time. The limit of detection, precision and accuracy have been established and the results obtained are compared with those obtained by simultaneous application of the spectrophotometric method, recomended by the Spanish legislation 6 which is similar to those adopted by ISO 7 and AOAC.8 Experimental Reagents and solutionsThroughout all the experimental work, analytical grade reagents were used; distilled and deionized water with a conductivity of less than 0.1 µS cm -1 was used throughout.The nitrite stock solution (0.1 M) was prepared from solid sodium nitrite which had been previously ovendried at 110˚C for 24 h. When necessary, the working solutions used in the calibration curves and in the standard addition method were prepared by rigorous dilution of the stock solution.The ionic strength adjuster (I.S.A) solution (2.0 M) was prepared from solid ammonium sulfate; chloride suppressor solution (0.16 M) was prepared from solid silver sulfate dissolved in ammonium hydroxide. ApparatusThe following equipment was used: a Perkin-Elmer Lambda 3B UV-V spectrophotometer,...

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