Utility of solid-phase spectrophotometry for determination of dissolved iron(II) and iron(III) using 2,3-dichloro-6-(3-carboxy-2-hydroxy-1-naphthylazo)quinoxaline

A new simple, very sensitive, selective and accurate procedure for the determination of trace amounts of iron(II) by solid-phase spectrophotometry (SPS) has been developed. The procedure is based on fixation of iron(II) as 2,3-dichloro-6-(3-carboxy-2-hydroxy-1-naphthylazo)quinoxaline on a styrene-divinylbenzene anion-exchange resin. The absorbance of resin sorbed iron(II) complex is measured directly at 743 and 830 nm. Iron(III) was determined by difference measurements after reduction of iron(III) to iron(II) with hydroxylamine hydrochloride. Calibration is linear over the range 1.0–20 μg L−1 of Fe(II) with relative standard deviation (R.S.D.) of 1.65% (n = 10.0). The detection and quantification limits for 100 mL sample system are 280 and 950 ng L−1 using 0.5 g of the exchanger. The molar absorptivity and Sandell sensitivity are also calculated and found to be 2.86 × 106 L mol−1 cm−1 and 0.0196 ng cm−2, respectively. The proposed procedure has been successfully applied to determine iron(II) and iron(III) in tap, mineral and well water samples.