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Spectrophotometric Determination of Selenium Through Triiodide Anion by Otilia Bizerea-Spiridon, Radu Nartita, Alexandru F. Rogobete, Adina Negrea, Ramona Stroescu, Teofana O. Bizerea, Constantin Ilie, Otilia Marginean

Background: Selenium is a chemical element found in the human body that plays a crucial role in its regulation. Depending on the concentration, it may have beneficial or have toxic effects. Selenium is incorporated as selenocysteine amino acid residue in selenoproteins which play an important role in many biological functions: anti-oxidant defense, regulation of the immune function and of the inflammatory response, metabolism of thyroid hormones, functioning of the central nervous system, biosynthesis of DNA and RNA, fertility, and reproduction. Excess selenium, altough less common than selenium deficiency, has equally important negative effects.
Methods: Given the importance of selenium quantification in various samples, the study proposes a simple and direct spectrophotometric determination of selenium using triiodide anions. The method is based on the oxidation of iodide in acidic medium by selenium (IV) contained in the sample, to form elemental iodine which, in turn, reacts with the excess iodide to form the triiodide anions, the most stable soluble species in aqueous solution. Triiodide is colored from yellow to brown, depending on the concentration. The coloured compound has maximum absorbance at specific wavelengths and thus, the stage of interaction with a chromogenic agent is eliminated. Due to the sensitivity of the reaction, the detection limit of triiodide, and therefore selenium, is extended toward lower values.
Results: The optimal conditions for the measurements were established: λ = 290 nm, pH = 1.0 - 1.5, reaction time = 15 minutes. Two areas of selenium detection were determined from the samples: 0.025 - 0.100 ppm, and 0.1 - 4.0 ppm. The detection limit of selenium was lowered at 0.100 ppm and even at 0.025 ppm, which significantly improves the sensitivity of the determination. Types of samples were specified which are suitable for analysis using the proposed method and explained why, in case of biological fluids, it must be used only accompanied by an adequate digestion method of the samples.
Conclusions: Selenium can be measured by direct spectrophotometric determination of the triiodide anion resulting from the oxidation of iodide by selenium (IV) compounds from the sample. In this regard, a simple, direct, and sensitive determination method of selenium from the samples by UV-Vis spectrophotometry, without the use of chromogenic agents has been optimized.

DOI: 10.7754/Clin.Lab.2016.160905