Simultaneous separation and microdetermination of cobalt(II), nickel(II) and copper(II)

Abstract

A sensitive and selective flotation procedure for the separation of microamounts of Co(II), Ni(II) and Cu(II) separately or in admixture is described. The maximum separation rate (∼ 1) for 0.1 mmol/L of each analyte is achieved using 1 mmol/L of both oleic acid (HOL) surfactant and 4-phenylthiosemicarbazide (HPTS) as a collector in the pH range 6–7. A method for the simultaneous separation and microdetermination of the analytes is elaborated, based on adding excess HPTS and floating the species with HOL at pH ∼6. The filtrate (which is clear brownish-yellow) obtained from the scum is used for the spectrophotometric determination of Co(II) at 350 nm. The formation constants of 1:1 and 1:2 [Co(II):HPTS] species are 6.9 × 10⁵ and 1.22 × 10¹⁰ L mol⁻¹, respectively. Beer’s law is obeyed up to 9 μg/mL of Co(II) with a molar absorptivity of 1.15 × 10⁴ L mol⁻¹ cm⁻¹. The precipitate in the scum layer is quantitatively collected, dissolved in aqua regia and aspirated directly into the flame for the (AAS) determination of Ni and Cu. The procedure is successfully applied to some natural water samples. A mechanism for the separation of the analytes is proposed.