Ionic solutes near critical conditions

The critical parameters (6) exclude immiscibilities in aqueous solutions near room temperature, where T > 0.5. Nevertheless, liquid-liquid coexistence curves were found at such conditions for some tetraalkylammo-nium salts with large cations and large anions [75-77]. In early debates of ionic criticality, this observation led to some confusion. Originally studied near the UCST [77], such gaps later proved to be closed loops with the LCST suppressed by crystallization [72,78]. In one case, the LCST could be reached [79, 80],... 

In the present article, we review recent progress in this subject area. In Sec. 2, we give a short overview on the chemical composition of the low melting salts and ILs. In Sec. 3 we address the problem of the electrolyte solution structure at conditions of low reduced temperature, where phase separations are known to occur. In Sec. 4, we consider experimental and theoretical results concerning the location of the two-phase regime in solutions of ionic fluids. In Sec. 5 we finally review theoretical and experimental results on near-critical behavior of ionic fluids. 

Reversed-Phase Liquid Chromatography (RPLC) is an important tool in protein chemistry. Examination of sorption isotherms revealed that alcohohc buffers did not desorb proteins near physiological pH in RPLC systems, while buffers containing a poly(ethoxy alcohol) surfactant did not desorb protein at pH 2, but they did at pH 7 with concentrations of surfactant apparently well above the critical micellar concentration (cmc) [2]. It has been proposed that a necessary condition for the desorption of a protein from a surface is that the surface tension of the solvent falls between that of the protein and the surface [6]. This condition is fiilfilled for many proteins with surfactant solutions near conditions of physiological pH and ionic strength. Therefore, it was expected that separations of proteins could be thieved in these conditions. 

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