Abstract: A catalytic spectrophotometry for the determination of trace selenium (IV) based on its catalytic effect on discoloring reaction of oxidation of with potassium bromate in weak acid solution and in the presence of microemulsion medium is described. The above reaction is followed spectrophotometrically by measuring the decrease in the absorbance at 450 nm for the catalytic reaction of 5-NO2-PADAP. Under optimum conditions, the calibration graph is linear in the range of 0.0～1.0 μg/L of Se (IV) at 450 nm. The detection limit achieved is 0.013μg/L. Combined with sulphydryl dextrane gel (SDG) separation and enrichment, the method has been successfully applied to the determination of Se (IV) in foodstuff and human hair samples with the relative standard deviation of 2.9 %～4.3 % and the recovery of 96.3 %～103.8 %, the results are in good agreement with those provided by ICP-AES method.

Key words: catalytiv kinetic spectrophotometry, selenium (IV), 2-(5-nitro-2-pyridylazo)-5-diethylaminophenyl (5-NO2-PADAP), microemulsion medium, separation, enrichment