An online ionic liquid-based microextraction system coupled to electrothermal atomic absorption spectrometry for cobalt determination in environmental samples and pharmaceutical formulations

Abstract

In the present work, an ionic liquid (IL) lighter than water was employed as extraction solvent in a dispersive liquid–liquid microextraction (DLLME) methodology. An original flow injection system for online microextraction and preconcentration of cobalt (Co) based on the use of tetradecyl(trihexyl)phosphonium chloride (CYPHOS® IL 101) was designed. Cobalt was complexed with 4-(2-pyridylazo)-resorcinol (PAR) reagent at pH 4.8 and then, the IL-DLLME procedure was developed by dispersing CYPHOS® IL 101 with acetone in an aqueous solution containing Co–PAR complex. Different pyridylazo dyes were evaluated for Co preconcentration in terms of their molecular structure, stability and acid–base equilibrium. Online extraction of Co–PAR into the IL and separation of the dispersed IL enriched phase were accomplished with a microcolumn containing Florisil material. Cobalt was removed from the microcolumn with a 10% (v/v) HNO₃ acidified-acetone solution and finally measured by electrothermal atomic absorption spectrometry (ETAAS). The detection limit achieved after preconcentration of 2 mL of sample solution was 8 ng L⁻¹. The precision for 10 replicate determinations at the 1 µg L⁻¹Co level was 5.1% relative standard deviation (RSD), calculated from the peak heights obtained. The method was successfully applied to Co determination in water samples as well as ophthalmic and parenteral solutions. For the first time, an IL-based microextraction technique was applied for metal determination in these complex samples, where Co recovery varied between 97.9 and 103%.