Modification of the methylene blue method for spectrophotometric selenium determination

The spectrophotometric method for Se(IV) determination based on its catalytic effect in the reduction of Methylene Blue (MB) by sulphide is modified. The variables that affect the decolorization of MB were taken into account: reagent concentrations, order of addition, mixing and standing times, pH, ionic strength, temperature, solution volume, wavelength, etc. The results of this study allowed a decrease of the determination limit and, by selection of the appropriate analytical conditions, choice of optimum linear range according to the selenium content in the sample. The lower limit range is 15-75 mug/1., with 3% relative standard deviation and no systematic errors. Procedures for overcoming several potential interferences were studied. The proposed method was applied to several environmental samples and the results were compared with those obtained by other standard methods.