Speciation of Fe(III) and Fe(II) in Water Samples by Means of a Sequential Flow-Through Biparameter Sensor with Two Sensing Zones

R. G. PELLERANO, P. ORTEGA-BARRALES, F. A. VAZQUEZ AND A. MOLINA-DÍAZ

Huelva - España

Congreso; SIMEC 2004 - Metal bound to biomolecules: Metallomics; 2004

Iron is widely distributed in nature and is one of the most important elements in biological systems . Its biological effectiveness is influenced by its chemical properties, such as valence, solubility, degree of chelation or complex formation. Interconversion between Fe2+ and Fe3+ is an essential biological property of iron utilized by microorganisms, plants, and animals for oxidative metabolism and in assimilating the metal . The ferrous iron in water is spontaneously oxidized by oxygen to highly insoluble ferric hydroxide; living organisms have developed iron-binding proteins and low molecular weight iron chelators, or siderophores to overcome this limited solubility. So, monitorization methods for Fe (II) and Fe (III) in water samples are needed. In this work, a flow-through biparameter spectrophotometric optosensor has been developed for the sequential determination and speciation of iron (II) and iron (III) in water samples. The method is based on the alternate retention of the Fe (II)- 1,10- phenantroline and Fe(III)-SCN complexes on two different sensing zones placed in two conventional flow cells in a double beam spectrophotometer: Sephadex SP C-25 in the sample beam for the detection of the cationic Fe (II)- 1,10- phenantroline complex and Sephadex-QAE-25 in the reference beam for the determination of anionic Fe(III)-SCN. Therefore, alternate positive and negative absorbance peaks from the baseline are obtained after two sequential sample injections when the carrier/self-eluting (NaCl 0.25 M) pass alternatively through each sensing zone by means of a selection valve. This is the first time that a spectrophotometric sensor of these characteristics working in the visible region is described. The influence of different experimental parameters such as concentration of reagents, reactor length, sample volume and flow–rate are investigated. Interference studies for several anions and cations are performed and no serious interference effects are observed. Calibration graphs with a linear range of 0.5-5 μg ml-1 was obtained for Fe(III) and Fe(II). This spectrophotometric biparameter sensor using two different materials as sensing zones was applied to Fe(III) and Fe(II) speciation in surface and spiked water samples.