Determination of trace iron in environmental water samples by flow injection catalytic spectrophotometry

Fe3+ had catalytic effect on the fading reaction of eriochrome blue black R oxidized by hydrogen peroxide in nitric acid medium.The concentration change of coloring agent was detected at 510 nm by flow injection automatic sampling technology and a new determination method of trace Fe3+ by flow injection catalytic kinetic spectrophotometry was established.The reaction medium,oxidizing agent,the volume ratio of nitric acid and hydrogen peroxide,the concentration of eriochrome blue black R,the reaction temperature and the pump speed were optimized.The effect of interference ions was investigated.The ions with serious interference such as copper and lead were masked by sodium thiosulfate to eliminate the interference.The linear range of this method was 0.08-0.68 μg/mL,and the detection limit was 9.77×10-4 μg/mL.The relative standard deviation(RSD,n=11) of 0.2 μg/mL Fe3+ was 0.4 %.The analytical speed was 48.6 times/h.The proposed method could be applied to the determination of trace iron (Ⅲ) in environmental water samples such as rain water,tap water and river water.