Analytical Sciences

Indirect Spectrophotometric Determination of Small Amounts of Selenium(IV) and Arsenic(V) by Simple Extraction Using Flotation Columns

Gamal Abd El-Hafeez MOSTAFA* and Shaban El-Syed GHAZY**

*Microanalytical Laboratory, Applied Organic Chemistry, National Research Center, Dokki, Cairo, Egypt
**Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt

A simple, rapid and selective procedure for the indirect spectrophotometric determination of Se(IV) and As(V) has been developed. It is based on the reduction of Se(IV) to Se(0) and As(V) to As(III) with hydroiodic acid (KI + HCl). The liberated iodine, equivalent to each analyte, is quantitatively extracted with oleic acid (HOL) surfactant. The iodine-HOL system exhibits its maximum absorbance at 435 nm. The different analytical parameters affecting the extraction and determination processes have been examined. The calibration graphs were found to be linear over the ranges 5 - 120 and 0.25 - 20 ppm of Se(IV) and As(V), with lower detection limits of 2.5 and 0.15 ppm and molar absorptivities of 1 x 10⁴ and 0.5 x 10⁴ dm³ mol^-1 cm^-1, respectively. Sandell's sensitivity was calculated to be 0.0078 and 0.0149 ug/cm² in the same order. The relative standard deviation for five replicate analyses of 40 ppm Se(IV) and 4 ppm As(V) were 1.0 and 0.9%, respectively. The proposed procedure in the presence of EDTA as a masking agent for foreign ions has been successfully applied to the determination of Se(IV) in a reference sample and As(V) in copper metal, in addition to their determination in spiked and polluted water samples.

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