[Speciation analysis of selenium by flow-injection catalytic spectrophotometry].

A new flow-injection catalytic spectrophotometric method was proposed for the determination of Se(IV) based on its catalytic effect on the reduction reaction of azure I by Na2S in pH 7.0 citric-acid sodium-hydrogen-phosphate buffer solution. Some different schematic diagrams of FIA were compared. Effects of the flow rates of reagents and sample, the medium and its acidity, the temperature, and coexistent substances were studied respectively. The amount of used reagents and the experimental conditions for sampling volume and coil length were optimized by using the controlled and weighed centroid simplex method. The Linear range of the determination is 0.1-2.0 mg x L(-1), the detection limit is 0.015 mg x L(-1), the relative standard deviation is less than 3.1%, and the sampling frequency is 120 samples per hour. The method has been applied to the determination of organic selenium and inorganic selenium in garlic and selenium-yeast. It was found that garlic had a strong enriching effect for selenium, and the conversion ratio of organic selenium decreased with increasing the concentration of selenium in the environment. The recovery of this method is 97.1%-104.3%.