Ionic-Liquid-Based Aqueous Biphasic Systems with Controlled pH: The Ionic Liquid Anion Effect

Abstract

This work addresses the effect of different anions in imidazoliumbased ionic liquids (ILs) through the formation of aqueous biphasic systems (ABS) using a phosphate buffer solution (KH 2 PO 4 /K 2 HPO 4 mixture of salts) aiming at controlling the pH value of the coexisting aqueous phases. Twelve ABS were investigated and the corresponding solubility curves were determined by the cloud point titration method at 298 K. In general, the IL anions aptitude to induce the formation of ABS increases with the decrease of the ability of the ions to form hydration complexes, i.e., with the decrease on the hydrogen-bond basicity of individual fluids. This trend is in close agreement to that observed in ABS with different inorganic salts, showing that the ILs rank is not dependent on the saltingout species used.

Evaluation of the impact of phosphate salts on the formation of ionic-liquid-based aqueous biphasic systems

“…Impurities may also affect the IL surface, making reproducibility difficult to achieve [56]. Nevertheless, the presence of impurities affecting these experiments can be overruled by the close agreement between them and previous results from our group [19] as well as from others [31,59] The combination of K 2 HPO 4 + KH 2 PO 4 (1.00 m + 1.09 m) to obtain a phosphate buffer solution at a neutral pH (7.0) and to be used in ABS formation was addressed in a previous study [44]. Nevertheless, to complete the study, new data for [C 4 3 CO 2 ] were obtained in this work.…”

“…The results here obtained, along with data from previous works using K 3 PO 4 [19] and a buffered mixture KH 2 PO 4 / K 2 HPO 4 [44] enabled us to gather a broader picture on the evaluation of the influence of both the salt's anion charge and ionic liquid anion towards the formation of ABS.…”

“…Making use of the experimental data obtained in this work and those already published [19,44], the main results can be grouped in four sets of phosphate-based ABS from highest to the least charge bearer salt: (1) In figure 2, the closer the curve is to the axes the larger the biphasic area and the stronger the demixing ability of the ionic liquid anion. On the systems here studied we found that ability to increase in the order:…”

“…When considering also the ILs studied previously [44] with this mixture of salts a broader ranking is obtained and is displayed in table 3. All these systems present consistently higher saturation solubility values when compared with the corresponding ones using K 2 HPO 4 salt solution alone, thus revealing the importance of pH in the interactions among all ions present in solution and/or the importance of substituting a stronger salting-out anion (HPO 2À 4 ) by a weaker one (H 2 PO À 4 ).…”

Pesticide Removal from Aqueous Solutions by Adding Salting Out Agents

“…The information coming from the literature [29] indicates that just experimental data related to the system composed of C 2 C 1 im C 1 SO 4 and K 2 HPO 4 are available and a very good agreement is obtained.…”