Chemical equilibria and sequential extractive spectrophotometric determination of selenium(IV) and (VI) using the chromogenic reagent 4,4′-dichlorodithizone

Abstract

The chromogenic reagent 4,4′-dichloro(3-mercapto-1,5-diphenylformazan), Cl2H2D Z , forms a yellow–red-coloured complex with selenium(IV). The produced complex species was extracted quantitatively into n-hexane, and its absorbance was measured at 416 nm. The chemical composition of the extracted selenium(IV)-Cl2H2D Z chelate and the molar absorptivity at 416 nm were found to be [SeO (Cl2HD Z )2] and 9 × 104 L mol−1 cm−1, respectively. The values of the extraction constants (K D, K ex, β) enable a convenient application of the proposed system for the liquid–liquid extraction procedure and sequential spectrophotometric determination of traces of inorganic selenium(IV) and/or selenium(VI) after reduction of the later to selenium(IV) with HCl (6 M). Beer's law and Ringbom's plots were obeyed in the concentration range 0.01–20 and 0.5–19 µg mL−1 of selenium(IV), respectively, with a relative standard deviation of 2.2%. The proposed method has been successfully applied to the determination of selenium(IV) or (VI) and total inorganic selenium(IV) and (VI) in tap and freshwater samples.