Kinetic Spectrophotometric Method for the Determination of Selenium (IV) by Its Catalytic Effect on the Reduction of Arsenazo III with Sodium Hypophosphite in Micellar Media

摘要

A simple and sensitive kinetic spectrophotometric method for the determination of trace selenium (IV) is described, based on its catalytic effect on the reduction arsenazo III (AsA III) with sodium hypophosphite (NaH_2PO_2) in a solution of 0.02 mol/L sulfuric acid and in the presence of cationic micellar media. The reaction rate is monitored spectrophotometrically by measuring the decrease in absorbance of AsA III at 550 nm with a fixed-time method. The decrease in the absorbance of AsA III is proportional to the concentration of Se(IV) in the range 0.16-1.0μg/L after a fixed time of 4-10 min from the initiation of the reaction. The limit of detection is 0.049μg/L Se(IV). The influence of the factors such as acidity, concentration of reactants, type and concentration of surfactants, reactive time, temperature and co-existing ions on the reaction is discussed. The optimum reaction conditions of reaction are established and some kinetic parameters are determined; the apparent activation energy of catalytic reaction is 59.51 kJ/mol. The relative standard deviation for eleven replicate determination of 0.02, and 0.01μg/25 mL Se(IV) was 2.0% and 2.4%, respectively. Combined with sulphydryl dextrane gel (SDG) separation and enriching, the method has been successfully applied to the determination of Se (IV) in foodstuff and human hair samples with the relative standard deviation of 2.1%-5.8% and the recovery of 97.0%-103.3%, the results are in good agreement with those provided by ICP-AES method.