Determination of Iron in Tap and Waste Water Using Liquid–Liquid Extraction in a Flow-Injection System

Abstract.

A flow-injection procedure for the determination of iron(III) in water is described. The procedure is based on the formation of an ion pair between the tetraphenylarsonium (Ph₄As⁺) (TPA) or tetrabutylammonium (But₄N⁺) (TBA) cations and the tetrathiocyanatoferrate(III) complex (TTF). This ion pair is extracted with chloroform, and the absorbance of the organic phase is measured at 503 nm (for Ph₄As⁺) or 475 nm (for But₄N⁺). Iron concentrations higher than 0.9×10⁻⁶ mol L⁻¹ (50 µg L⁻¹) can be detected in the first case, with a relative standard deviation of 1.9% (n=12), a linear application range’of between 1.34 and 54.0×10⁻⁶ mol L⁻¹ (75–3015 µg L⁻¹), and a sampling frequency of 30 h⁻¹. For the ion pair with But₄N⁺, the detection limit is 0.52×10⁻⁶ mol L⁻¹ (29 µg L⁻¹), with a relative standard deviation of 1.6% and a linear application range between 0.73 and 54.0×10⁻⁶ mol L⁻¹. Under the proposed working conditions, only Pd(IV), Cu(II) and Bi(III) interfere. With the application of the merging zones technique, considerable amounts of organic reagent can be saved. The TBA method was applied to the analysis of iron(III) in tap and industrial waste waters.