A flow-through fluorescent sensor to determine Fe(III) and total inorganic iron

A flow-through fluorescent sensor for the consecutive determination of Fe(III) and total iron is described. The reactive phase of the proposed sensor, which has a high affinity for complexed Fe(III), consists of pyoverdin immobilized on controlled pore glass (CPG) by covalent bonding. This pigment selectively reacts with Fe(III) decreasing its fluorescence emission. Total inorganic iron is determined as Fe(III) after on-line oxidation in a mini-column containing persulphate immobilized on an ion exchange resin. The developed method allows the determination of Fe(III) in the 3-200 (g l(-1) range. The relative standard deviations of 10 determinations of 60 (g l(-1) of Fe(III) and 20 (g l(-1) of Fe(III)+Fe(II) are 3 and 5%, respectively. The sensor has been satisfactorily applied to speciate iron in synthetic, tap and well waters and wines. There were no significant differences for total inorganic iron determination between this new method and the atomic absorption spectroscopy reference method at the 95% confidence level. The sensor allows the concentration of Fe(II) to be calculated as the difference between total inorganic iron and Fe(III). The lifetime of the sensor is at least 3 months in continuous use or the equivalent of 1000 determinations.