Simultaneous flow injection determination of iron(II) and iron(III) with opto-electrochemical detection

A two line manifold flow injection system with opto-electrochemical detection (simultaneous optical and electrochemical detection) is described for the simultaneous determination of Fe(II) and Fe(III). A modified Z-type flow cell is operated simultaneously as an optical flow cell for the spectrophotometric determination of Fe(III) by monitoring the absorbance of the sulfosalicylic acid–Fe(III) complex at 505 nm and as an electrochemical flow cell for amperometric monitoring of the current due to the oxidation of Fe(II) to Fe(III) at potential of +1.0 V vs. SCE. The optical and electrochemical signals are recorded simultaneously by two recorders. The calibration graphs are linear in the ranges 1×10−6–4×10−4 M for Fe(III) and 1×10−5–3×10−3 M for Fe(II). The 3σ limits of detection of Fe(III) and Fe(II) are 4.3×10−7 and 5.6×10−6 M, respectively. The relative standard deviation of 16 determinations of 4×10−5 M of Fe(III) and 1×10−4 M of Fe(II) are 1.00% and 1.39%, respectively. Up to 75 samples per hour can be determined. The effects of several common ions on the determination of Fe(II) and Fe(III) are studied, showing that the method is relatively free from interferences. The method is applied to the simultaneous determination of Fe(II) and Fe(III) in spiked tap water.