Abstract: Trace Fe(Ⅲ) catalyzes the discoloring oxidation reaction of arsenazo Ⅲ by potassium periodate(KIO₄) in sulfuric acid medium.The kinetic conditions have been studied in detail.A new method of kinetic spectrophotometry for the determination of trace Fe(Ⅲ) is established.The sensitivity of method is 8 ng/L.The range of measurement is 0～0.06mg/L Fe(Ⅲ).The coexisting metal ions can be separated by mercapto-containing dextran gel.This method has been applied to the determination of trace iron(Ⅲ) in water and human hair samples with satisfactory results.

Key words: catalytic-kinetic spectrophotometry, mercapto-containing dextran gel, iron (Ⅲ)