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

The chromogenic reagent 4,4'-dichloro(3-mercapto-1,5-diphenylformazan), Cl2H2DZ, 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)-Cl2H2DZ chelate and the molar absorptivity at 416 nm were found to be [SeO (Cl2HDZ)(2)] and 9 x 10(4) L mol(-1) cm(-1), respectively. The values of the extraction constants (K-D, K-ex, beta) 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 mu g 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.