Supported liquid membranes selectivity

ABSTRACT. Synthetic receptor molecules derived from calix[4]arenes have been used in different technological applications. The use of various functionalized calix[4]arenes in selective membrane transport through supported liquid membranes, selective cation detection with chemically modified field effect transistors, as preorganized donor-7c-acceptor systems in non linear optics and in the development of monolayers with receptor headgroups is discussed. 

ILs, on the other hand, are uniquely suited for use as solvents for gas separations. Since they are non-volatile, they cannot evaporate to cause contamination of the gas stream. This is important when selective solvents are used in conventional absorbers, or when they are used in supported liquid membranes. For conventional absorbers, the ability to separate one gas from another depends entirely on the relative solubilities (ratio of Henry s law constants) of the gases. In addition, ILs are particularly promising for supported liquid membranes, because they have the potential to be incredibly stable. Supported liquid membranes that incorporate conventional liquids eventually deteriorate because the liquid slowly evaporates. Moreover, this finite evaporation rate limits how thin one can make the membrane. This... 

Zougagh, M., Valcarcel, M., and Rios, A., Automatic selective determination of caffeine in coffee and tea samples by using a supported liquid membrane-modified piezoelectric flow sensor with molecularly imprinted polymer. Trends Anal. Chem., 23, 399, 2004. 

Classical LLEs have also been replaced by membrane extractions such as SLM (supported liquid membrane extraction), MMLLE (microporous membrane liquid-liquid extraction) and MESI (membrane extraction with a sorbent interface). All of these techniques use a nonporous membrane, involving partitioning of the analytes [499]. SLM is a sample handling technique which can be used for selective extraction of a particular class of compounds from complex (aqueous) matrices [500]. Membrane extraction with a sorbent interface (MESI) is suitable for VOC analysis (e.g. in a MESI- xGC-TCD configuration) [501,502]. 

Liquid membrane enrichment coupled on-line with ion chromatography. Low molecular mass carboxylic acids in low concentrations in air or soil samples can be determined by ion chromatography coupled on-line to a selective enrichment system consisting of a supported liquid membrane, impregnated with tri- -octylphosphine oxide in di-n-hexyl ether [97-98]. The system allows the determination of these carboxylic acids at micromolar levels in the presence of interfering ions such as nitrite, chloride, sulfate, iron, and aluminum. 

Other applications of supported liquid membranes have been related to metal speciation. For example, recently a system for chromium speciation has been developed based on the selective extraction and enrichment of anionic Cr(VI) and cationic Cr(III) species in two SLM units connected in series. Aliquat 336 and DEHPA were used respectively as carriers for the two species and graphite furnace atomic absorption spectrometry used for final metal determination. With this process, it was possible to determine chromium in its different oxidation states [103]. 

Affinity of MIP towards the target analyte should be examined prior to fabrication of the chemosensor. Batch binding assays are used to test selectivity of suitable MIPs. Especially, affinity of MIP to compounds, which are structurally related to the target analyte, should be tested. If MIP binds similarly with these compounds as the template, then cross-reactivity is manifested [156], This effect was exploited for determination of adenine and its derivatives with the use of MIP templated with 9-ethyladenine. Nevertheless, the cross-reactivity, if undesired, can be avoided by suitable sample pretreatment, e.g. by interferant extraction with a supported liquid membrane (SLM) coupled to the MIP-PZ chemosensor. The Fluoropore membrane filter of submicrometre porosity can serve that purpose. That way, this membrane holds interferants, thus eliminating the matrix effect. The SLM-involving determination procedure is cheaper than traditional laborious sample pretreatment used to remove the interfering substances. For instance, caffeine [143] and vanillin [157] in food samples have been determined using this procedure. 

Mohapatra, P.K. Lakshmi, D.S. Mohan, D. Manchanda, V.K. Selective transport of cesium using a supported liquid membrane containing di-t-butyl benzo 18 crown 6 as the carrier, J. Membr. Sci. 232 (2004) 133-139. 

Asfari, Z., Bressot, C., Vicens, J., Hill, C., Dozol, J.-F., Rouquette, H., Eymard, S., Lamare, V., Toumois, B. Doubly Crowned Calix[4]arenes in the 1,3-Altemate Conformation as Cesium-Selective Carriers in Supported Liquid Membranes. Anal. Chem. 67 (1995), 3133-3139. 

Figure 8.3 Schematic representation of copper concentrations relevant to freshwater studies and analytical windows of several analytical techniques. ASV, anodic stripping voltammetry CSV, cathodic stripping voltammetry ISE, ion selective electrode SLM, supported liquid membrane SWASV, square wave anodic stripping voltammetry LC50, lethal concentration for 50% of the population [Cu]t, total metal concentration (adapted from Langford and Gutzman, 1992).

Parthasarathy, N., J. Buffle, N. Gassama, and F. Cuenod. 1999. Speciation of trace metals in waters Direct selective separation and preconcentration of free metal ion by supported liquid membrane. Chem. Anal. 44 455 170. 

Tudorache, M. and J. Emneus. 2005. Selective immuno-supported liquid membrane (ISLM) extraction, enrichment and analysis of 2,4,6-trichlorophenol. J. Membr. Sci. 256 143-149. 

Belkhouche, N.E., Didi, M.A., Romero, R., Jonsson, J.A. and Villemin, D. (2006) Study of new organophosphorus derivates carriers on the selective recovery of M(II) and M(III) metals, using supported liquid membrane extraction. Journal of Membrane Science, 284, 398. Schlosser, S. (1997) Method and equipment for mass and heat transfer among several liquids (in Slovak), Slovak pat. No. 278547. 

Wijers, M.C., Jin, M., Wessling, M. and Strathmann, H. (1998) Supported liquid membranes modification with sulfonated poly(ether ether ketone) - permeability selectivity and stability Journal of Membrane Science, 147, 117. 

Membrane Techniques The interest in membrane techniques for sample preparation arose in the 1980s. Extraction selectivity makes membrane techniques an alternative to the typical sample enrichment methods of the 1990s. Different membrane systems were designed and introduced into analytical practice some more prominent examples are polymeric membrane extraction (PME), microporous membrane liquid-liquid extraction (MMLLE), and supported liquid membrane extraction (SEME) [106, 107]. Membrane-assisted solvent extraction (MASE) coupled with GC-MS is another example of a system that allows analysis of organic pollutants in environmental samples [108-111] ... 

Nonporous membrane techniques involve two or three phases separated by distinct phase boundaries. In three-phase membrane systems, a separate membrane phase is surrounded by two different liquid phases (donor and acceptor) forming a system with two phase-boundaries and thus two different extraction (partition) steps. These can be tailored to different types of chemical reactions, leading to a high degree of selectivity. The membrane phase can be a liquid, a polymer, or a gas, and the donor and acceptor phases can be either gas or hquid (aqueous or organic). Liquid membrane phases are often arranged in the pores of a porous hydrophobic membrane support material, which leads to a convenient experimental system, termed supported liquid membrane (SLM). There are several other ways to arrange a hquid membrane phase between two aqueous phases as described below. 

Chimuka L, Cukrowska E, Soko L, and Naicker K. Supported-liquid membrane extraction as a selective sample preparation technique for monitoring uranium in complex matrix samples. J. Sep. Sci. 2003 26 601-608. 

Palmarsdottir S, Lindegard B, Deininger P, Edholm L-E, Mathiasson L, and Jonsson JA. Supported liquid membrane technique for selective sample work-up of basic drugs in plasma prior to capillary zone electrophoresis. J. Capill. Electrophor. 1995 2 185-189. 

Palmarsdottir S, Thordarson E, Edholm L-E, Jonsson jA, and Mathiasson L. Miniaturized supported liquid membrane device for selective on-line enrichment of basic drugs in plasma combined with capillary zone electrophoresis. Anal. Chem. 1997 69 1732-1737. 

Norberg J, Emneus J, Jonsson jA, et al. On-line supported liquid membrane-liquid chromatography with a phenol oxidase-based biosensor as selective detection unit for the determination of phenols in blood plasma. J. Chromatogr. B. 1997 701 39 6. 

Teramoto M, Matsuyama H, Nakai K, Uesaka T, and Ohnishi N. Eacilitated uphill transport of eicosapentaenoic acid ethyl ester through bulk and supported liquid membranes containing silver nitrate as carrier A new type of uphill transport. J Mem Sci, 1994 91(1-2) 209-213. Teramoto M, Matsuyama H, and Ohnishi N. Selective facilitated transport of benzene across supported and flowing liquid membranes containing silver nitrate as a carrier. J Mem Sci, 1990 50 269-278. 

Shukala JP, Kumar A, and Singh RK. Macrocycle-mediated selective transport of plutonium (IV) nitrate through bulk liquid and supported liquid membranes using dicyclohexano-18-crown-6 as mobile carrier. Sep Sci Technol 1992 27 447 65. 

Supported liquid membranes, consisting of an organic solution of -octyl(phenyl)-A,iV-diisobutylcarbamoylmethylpho-sphine oxide (CMPO) and tributyl-phosphate (TBP) in decalin, were capable of selective separation and concentration of actinide and lanthanide ions from aqueous nitrate feed solutions and from synthetic nuclear wastes where the strip solution is a mixture of formic acid (FA) and hydroxylammonium formate (HAF) [106,107]. TBP is added to CMPO to improve its solubility in aliphatic diluents. Although low concentration of nitric acid was initially used as the strippant solution, a gradual... 

FIGURE 38.6 Example of a supported liquid membrane. The carrier (C) contained in the membrane micropore selectively transports the species i from the gas to the strip phase. 

The ability of calixarenes to bind large metal ions with high kinetic stability is important in the search for complexants for radionuclides such as Cs (ti/2 = 30.2 yr) and Sr (ti/2 = 65 d) from the reprocessing of exhausted nuclear fuel. There has been considerable interest in caesium-complexed calix[4]-bis-crowns as selective Cs-carriers. Transport isotherms of trace level Cs through supported liquid membranes containing calix[4]-bis-crowns have been determined as a function of the ionic concentration of the aqueous feeder solutions, and l,3-calix[4]-bis-o-benzo-crown-6 appears to be much more efficient in decontamination than mixtures of crown ethers and acidic exchangers, especially in highly acidic media. " ... 

One of the first applications of TSOSs was reported in 2002. Davis and his team have shown that an amine-derived imidazolium salt can capture carbon dioxide by forming a ammonium carbamate [28], Primary amine functionalized imidazolium salts have also been used for facilitating C02 transport through a supported liquid membrane showing high selectivity and high stability for CH4/C02 separation [50] (Fig. 18). 

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