A New Spectrophotometric Method for Determination of Selenium in Cosmetic and Pharmaceutical Preparations after Preconcentration with Cloud Point Extraction
A simple, rapid, and sensitive spectrophotometric method for the determination of trace amounts of selenium (IV) was described. In this method, all selenium spices reduced to selenium (IV) using 6？M？HCl. Cloud point extraction was applied as a preconcentration method for spectrophotometric determination of selenium (IV) in aqueous solution. The proposed method is based on the complexation of Selenium (IV) with dithizone at pH？<？1 in micellar medium (Triton X-100). After complexation with dithizone, the analyte was quantitatively extracted to the surfactant-rich phase by centrifugation and diluted to 5 mL with methanol. Since the absorption maxima of the complex (424？nm) and dithizone (434？nm) overlap, hence, the corrected absorbance, Acorr, was used to overcome the problem. With regard to the preconcentration, the tested parameters were the pH of the extraction, the concentration of the surfactant, the concentration of dithizone, and equilibration temperature and time. The detection limit is 4.4？ng mL-1; the relative standard deviation for six replicate measurements is 2.18% for 50？ng mL-1 of selenium. The procedure was applied successfully to the determination of selenium in two kinds of pharmaceutical samples. 1. Introduction Selenium (Se) has been recognized as an essential nutrient for plant, animal, and human body, but at high concentration it can become toxic. The range between the concentration in which selenium is essential and toxic is very narrow [1, 2]. This element plays an important role in elderly people as well as in the prevention of many age-associated diseases and in maintenance of normal immune function. Se is potent antioxidant involved in cellular defense against free radical reactions, and the risk of deficiency seems to increase in proportion to the age. Evidence is accumulating that most of the degenerative diseases have their origin in deleterious free radical reactions. These diseases include atherosclerosis, cancer, inflammatory joint, asthma, diabetes, senile dementia, and degenerative eye disease [3]. But high Se concentrations in human can cause loosing hair and nails and irritation of skin and eye [1]. Se is essential nutrient for human health. The required daily amount of Se is 20？mcg？day？1 and 40–70？mcg day？1 for 4–6 years old and adult males, respectively. The essential role of the Se is due to its presence in the active site of some enzymes (i.e., glutathione peroxidase and iodotironine-5-deiodinase) and the catalytic effect of selenium compounds on the reaction of intermediate metabolism and inhibition of the toxic
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