Determination of Trace Amounts of Total Fe as Fe(II) in Environmental Samples by Catalytic Kinetic Spectrophotometry

Abstract

The method is based on the selective catalytic effect of iron (II) ions in the presence of 1,10-phenanthroline as an activator, on the oxidation of Coomassie Brillant Blue 2R by bromate. The catalytic reaction was monitored spectrophotometrically at 520 nm by fixed time approach of 3 min. The optimization of the operating conditions are investigated. Obtained optimum conditions: 1.5 mL of Coomassie Brillant Blue 2R (1.0 x 10 -4 mol L -1 ), 0.6 mL of bromate (0.01 mol L -1 ), 1.5 mL of 1,10-phenanthroline (1.0 x 10 -3 mol L -1 ), reaction temperature 25 o C and time 3 min in pH 2.0 at 520 nm. The proposed method allows quantitatively determination of iron (II) in the range of 0.05-5 mg L -1 with a selectivity and quantification limit of 0.0141 and 0.047 mg L -1 . The relative standard deviations for five replicate determinations of 0.2 and 3 mg L -1 iron (II) are 3.8% and 2.3%, respectively. The method was applied to determination of total iron in some environmental surface waters such as lake, river and well water including pharmaceutical samples used in the treatment of iron deficiency (such as ferrosolanol and maltose) after pre-reduction of iron (III) to iron (II) with sulfite at 40 o C at pH 4.0, and quantitative percentages of retinas ranging from 98.7-102.7% were obtained by standard attachment-based analysis after wet acid dissolution for possible matrix effect.