Determination of dissolved iron(II) and iron(III) in water with 5-Br-PAN-Sby solid phase spectrophotometry

A very sensitive and selective method for the determination of trace amount s of iron(II) and iron(III) by SPS has been developed. It is based on the f ixation of iron(II) as 1-(5-bromo-2-pyridylazo)-2-naphthol-6-sulphonic acid (5-Br-PAN-S) complex on a styrene-divinylbenzene anion-exchange resins. Th e absorbances of resin sorbed iron(II) complex is measured directly at 765 and 850 nm. Iron(III) was determined by difference measurements after reduc tion of iron(III) to iron(II) with hydroxylamine. The linear range of the d etermination is 0-25 mug for iron(II) or total iron. The detection limit fo r a sample volume of 100 ml using 0.5 g of anion-exchange, corresponds to 2 .1 mug l(-1). The method has been successfully applied to the determination of iron(II) and iron(III) in drinking water and natural waters.