Ionic liquids partitioning methods

A three-phase liquid-liquid partitioning consisting of hexane, acetonitrile, and dichloromethane has also proven to be a preferred cleanup method for diethylstilbestrol and zeranol (455), trenbolone and epitrenbolone (445), trenbolone and nortestosterone (446), and melengestrol residues (456) in tissues. Following adjustment of the initial aqueous acetonitrile sample extract at pH 13, most of the polar and ionic acidic matrix components were directed into the aqueous layer during the partitioning process, while the low-polarity components were extracted... 

Several cleanup methods have been developed for the determination of urea pesticides, involving different basic procedures, such as liquid-liquid partition (30-32,34,36,37), steam distillation (31), and liquid-solid chromatography (9,30,32,34,36,38,56-58). Different factors, e.g., water solubility, ionic and polarity properties, thermal stability, and the molecular weight of the compounds, determine the choice of the cleanup method. Moreover, micro-cleanup procedures and online enrichment techniques have been introduced for the automated determination of phenylureas (60). Table 6 summarizes the use of the different cleanup procedures in the determination of urea pesticides. 

The interfacial potential drop at the nonpolarizable ITIES was controlled by varying the concentration of either the cation or the anion of the ionic liquid in the aqueous phase. The kinetics of interfacial ET followed the Butler-Volmer equation, and the measured bimolecular rate constant was much larger than that obtained at the water-1,2-dichloroethane interface. In the second publication, Laforge et al. [112] developed a new method for separating the contributions from the interfacial ET reaction and solute partitioning to the SECM feedback. 

Recently, various Hoveyda-type carbenes were attached to different resins or insoluble inorganic supports preferentially via the 2-alkoxybenzylidene fragment. An alternative method involves the use of tagged catalysts, which can be easily separated from untagged products by a phase-transfer event (precipitation or hquid-hquid partition). One particularly innovative method involves a catalyst immobilization in ionic liquids (IL). Because of their interesting properties such as ease of reuse, nonvolatility, and good ability to dissolve... 

Revelli, A.-L. Mutelet, F. Jaubert, J.-N. (2010a). Prediction of partition coefficients of organic compounds in ionic liquids Use of a linear solvation energy relationship with parameters calculated through a group contribution method. Ind. Eng. Chem. Res., 8,49, 3883-3892. 

Liquid-liquid extraction is used extensively and successfully (6). If the analytes are acidic or basic, as is often the case when HPLC is the analytical method selected, appropriate ionization suppression can be employed to affect the desired extraction. Back extraction of the analytes into an appropriately buffered aqueous volume can then serve to isolate and concentrate. Anionic and cationic surfactants, or so-called ion-pairing reagents, can be added prior to extraction to increase the partition coefficients of the trace organic ionic compounds. 

The most widely used type of HPl.C is panitiim chromatography, in which the stationary phase is a second liquid that is immiscible with the liquid mobile phase. In the past, most of the applications have been to nonionic, polar compounds of low to moderate molecular mass (usually --. TOIX)). Recently, however, methods have been developed (deriv atizatipn and ion pairing) that have e.xtended partition separations to ionic cumpound.s. 

Conventional approaches based on electrochemical techniques, surface tension, and extraction methods have allowed the estabhshment of thermodynamic and kinetic information concerning partition equilibrium, rate of charge transfer, and adsorption of surfactant and ionic species at the hquid/Uquid interface [4—6]. In particular, electrochemical methods are tremendously sensitive to charge transfer processes at this interface. For instance, conventional instm-mentation allowed the monitoring of ion transfer across a hquid/hquid interface supported on a single micron-sized hole [7, 8]. On the other hand, the concentration profile of species reacting at the interface can be accurately monitored by scanning electrochemical microscopy [9, 10]. However, a detailed picture of the chemical environment at the junction between the two immiscible liquids caimot be directly accessed by purely electrochemical means. The implementation of in-situ spectroscopic techniques has allowed access to key information such as ... 

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