Determination and speciation of Se(IV), Se(VI), and selenomethionine in iranian walnut samples by spectrophotometry after cloud point extraction

A sensitive and selective micelle-mediated speciation and preconcentration method has been developed for trace amount of inorganic and organic selenium prior to UV-Vis spectrophotometry determination. The method is based on cloud point extraction of Se(IV) ions with polyethylene glycol tert-octylphenyl ether (Triton X-114) in presence of 2,3-diaminonaphthalene (DAN) as a chelating agent. Se(IV) ions react with DAN in a surfactant solution yielding a hydrophobic complex at pH 3. The phase separation was accelerated by a 20 min centrifugation at 3500 rpm. The calibration graph obtained from Se(IV)-DAN complexes was linear in the concentration range of 5.0–400.0 ng/mL and detection limit was 9 ng/mL. The relative standard deviation was 1.6% in the determination of 80 ng/mL Se(IV). The proposed method was successfully applied to the speciation and determination of selenium species-Se(IV), Se(VI), selenomethionine—in walnut samples with satisfactory results.