A flow injection spectrophotometric method has been developed for the determination of iron (II) and iron (III) in environmental waters. The procedure was based on the reduction of iron (III) to iron (II) by ascorbic acid and complexation of iron (II) with 4-(2-pyridylazo) resorcinol, with the presence of ammonia, the absorbance was measured at 718 nm, difference from the complexation of other metals with 4-(2-pyridylazo) resorcinol. The calibration graph is linear in the range of 1times10 -9 -1times10 -7 g ml -1 and 5times10 -8 -1times10 -5 g ml -1 . The detection limit is 3times10 -10 g ml -1 . The relative standard deviation was 2.1% for 1times10 -8 g ml -1 iron(II) (n=11), 2.8% for 5-10 -7 g ml -1 iron(II) (n=11). This method is very simple, rapid and suitable for automatic and continuous analysis. The proposed method was applied to the determination of iron (III) and iron (II) in tap water, river water and groundwater successfully.
