Flotation–Spectrophotometric Determination of Mercury in Water Samples Using Iodide and Ferroin

Abstract

This paper describes a simple and highly selective method for separation, preconcentration and spectrophotometric determination of trace amounts of mercury. The method is based on the flotation of an ion-associate of HgI₄^2– and ferroin between aqueous and n-heptane interface at pH 5. The ion-associate was then separated and dissolved in acetonitrile to measure its absorbance. Quantitative flotation of the ion-associate was achieved when the volume of the water sample containing Hg(II) was varied over 50–800 ml. Beer’s law was obeyed over the concentration range of 3.2 × 10^–8–9.5 × 10^–7 mol l^–1 with an apparent molar absorptivity of 1 × 10⁶ l mol^–1 cm^–1 for a 500 ml aliquot of the water sample. The detection limit (n = 25) was 6.2 × 10^–9 mol l^–1, and the RSD (n = 5) for 3.19 × 10^–7 mol l^–1 of Hg(II) was 1.9%. A notable advantage of the method is that the determination of Hg(II) is free from the interference of the almost all cations and anions found in the environmental and waste water samples. The determination of Hg(II) in tap, synthetic waste, and seawater samples was carried out by the present method and a well-established method of extraction with dithizone. The results were satisfactorily comparable so that the applicability of the proposed method was confirmed in encountering with real samples.