Ionic liquid for homogeneous liquid-liquid microextraction separation/preconcentration and determination of cobalt in saline samples

Abstract

A novel homogeneous liquid-liquid microextraction technique based on use of ionic liquids (ILs), termed in situ solvent formation microextraction (ISFME) is developed for separation/preconcentration of Co(II) ions. In this method, small amount of sodium hexafluorophosphate (NaPF₆, as an ion-pairing agent) was added to the sample solution containing very small amount of 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF₄], as hydrophilic IL). A cloudy solution was formed as a result of formation of fine droplets of 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim][PF₆]. After centrifuging, the fine droplets of the extractant phase settled to the bottom of the conical-bottom glass centrifuge tube. ISFME is a simple and rapid method for extraction and preconcentration of cobalt ions from water samples that can be applied for the sample solutions containing very high concentrations of salt. Furthermore, this technique is much safer in comparison with the organic solvent extraction. Reliability of the introduced methodology was evaluated by analyzing water reference material. ISFME was successfully applied to determining cobalt(II) in real water samples. Schiff base ligand, 3,3′-(1E,1E′)-(propane-1,2-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(4-bromophenol) (L) was chosen as a complexing agent. Analysis was carried out using atomic absorption spectrometry. Type and amount of IL, pH and the other parameters were optimized. Under the optimum conditions, the limit of detection (LOD) was 0.06 ng/mL and the relative standard deviation (RSD) was 1.8% for 10 ng/mL cobalt.