Supported liquid membrane extraction selectivity

Classical LLEs have also been replaced by membrane extractions such as SLM (supported liquid membrane extraction), MMLLE (microporous membrane liquid-liquid extraction) and MESI (membrane extraction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]. 

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. 

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] ... 

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. 

The supported liquid membrane extraction is generally one of the most selective membrane based extraction techniques. Selectivity is tuned by adjusting the foctors described above. However, like other membrane based extraction techniques, so far it has been applied to mostly environmental and biological samples as seen in review articles (30,31,34). 

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. 

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. 

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. 

Zaghbani, A., Tayeb, R., Dhahbi, M., Hidalgo, M., Vocanson, F., Bonnamour, I., Seta, P., Fontas, C. (2007). Selective thiacalix[4]arene bearing three amide groups as ionophore of binary Pd(II) and Au(III) extraction by a supported liquid membrane system. Sep. Purif. Technol., 57, 374-9. 

LIX 64N hes been used to separate nickal ions as well as copper.20 22 The chemistry of extraction in the two cases is the same [see Eqs. (19.4-3) and (19.4-4)]. However, data on transport throngh supported liquid membranes suggest that the copper flux across the membrane to fonr times that of nickal and selective extraction of copper can be achieved.22 The compound di-Q-elhylhexyl) phosphoric acid also has besn proposed for die essraciion of nickel II using liquid membranes,35... 

A new and promising way of combining reaction and extraction are supported liquid membranes (SLM). Miyako et al. used SLMs on the basis of different water-immiscible ionic liquids and aliphatic hydrocarbons to achieve pure (S)-ibuprofen together with an enzymatic resolution step (Scheme 8-6). Only the (S)-enantiomer is esterified by the enzyme attached to the feed interface and able to enter the membrane. The ionic-liquid phase allows the selective transport of the more hydrophobic ibuprofen methyl ester from the aqueous-feed phase to the receiving phase. At the inter ce of the receiving phase, the (S)-ibuprofen methyl ester is hydrolysed to (S)-ibuprofen by another lipase. As (S)-ibuprofen is more hydrophilic it is not transported back through the supported ionic-Hquid phase. Best results were achieved with [BMIM]( (CFjSOijiN] as liquid membrane phase and the enzyme combination mentioned in Table 8-3 [85,86]. 

One promising technique to accomplish this task Is solid supported liquid membrane (SLM) transfer using new extractants that are selective for actinides of various valencies (1,2). Our previous work p), also has demonstrated the utility of this technique and Is reviewed and extended In this paper. 

Microemulsions have not been employed to any significant extent as liquid membranes in SLMs. Although it is not absolutely clear whether microemulsions have been placed within the pores of a solid microporous membrane support to serve as a liquid membrane, a study reported in one publication came very close to doing so. Osseo-Asare and Chaiko [14] used an extractant, dinonylnaphthalenesulfonic acid (HDNNS), to separate cobalt selectively from a multicomponent aqueous stream. In the presence of water, the HDNNS forms a microemulsion. Thus, the authors concluded that their supported liquid membrane, which was initially impregnated with HDNNS, was indeed a microemulsion (supported) liquid membrane once it contacted the aqueous feed and receiving phases. 

Radioactive waste management plant Selective actinide extraction Supported liquid membrane Spiral-wound reverse osmosis Solvent extraction Tri-n-butyl phosphate Total dissolved solids Tri-n-octylamine... 

---