Microporous membrane MMLLE

A new version of CPLLE can be performed as cross- and countercurrent flows of aqueous and organic phases separated by the microporous membrane (MMLLE) in the same devices used for SLM extraction (Figure 8). The organic phase wets the membrane better than an aqueous solution and enters the membrane pores. A leakage of the organic phase can be prevented by applying a suitably higher pressure on the aqueous side. 

Classical LLEs have also been replaced by membrane extractions such as SLM (supported liquid membrane extraction), MMLLE (microporous membrane liquid-liquid extraction) and MESI (membrane extraction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

MMLLE Microporous membrane liquid-liquid extraction... 

Microporous membrane liquid-liquid extraction (MMLLE) is a two-phase extraction setup. In MMLLE procedures, the membrane material and format (FS and HF), extraction units, and system configurations are identical to those described in SLM (Section 4.4.1.2).63 The two-phase HF-MMLLE system is identical to that used in Section 4.4.3, although sometimes with minor differences. In contrast to three-phase SLM extraction, MMLLE employs a microporous membrane as a miniaturized barrier between two different phases (aqueous and organic). One of the phases is organic, filling both the membrane pores (thus making the membrane nonporous) and the compartment on one side of the membrane (acceptor side). The other phase is the aqueous sample on the other side of the membrane (donor side). In this way, the two-phase MMLLE system is highly suited to the extraction of hydrophobic compounds (log Ko/w > 4) and can thus be considered a technique complimentary to SLM in which polar analytes (2 < log Ko/w < 4) can be extracted. 

MMLLE Microporous membrane liquid-liquid extraction Nonporous (microporous) Aqueous/organic/organic Organic/organic/aqueous... 

Application of polymer membranes to separation of aqueous and organic phases in liquid-liquid extraction processes is called microporous membrane liquid-liquid extraction (MMLLE). An organic acceptor solvent, filling the pores of the hydro-phobic membrane, stays in direct contact with the aqueous phase near the membrane surface, where mass transfer takes place. This kind of extraction is similar to SEME, but takes place in a two-phase system and is slower and less selective because of the absence of carrier agent. Because the polymer membranes are insoluble, an arbitrary combination of aqueous and organic phase is possible and the extraction efficiency mainly depends on the partition coefficient. 

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] ... 

Two-phase liquid membrane Microporous membrane liquid—liquid extraction MMLLE [6,86]... 

As with three-phase membrane extraction, it is also possible here to work either with flat membranes, or with hollow-fiber membranes. In the first case, the technique is usually called microporous membrane liquid-liquid extraction (MMLLE), a name originating from Cussler [40]. With hollow fibers, it can be called two-phase liquid phase microextraction. 

Note SLM, supported liquid membrane (aq/org/aq) MMLLE, microporous membrane liquid-liquid extraction (aq/org) PME, polymer membrane extraction (aq/polymer/org) MESI, membrane extraction with sorbent interface (aq (or gas)/polymer/gas/sorbent) CFLME, continuous flow liquid membrane extraction (aq/org (in flow)/aq) LPME2, two-phase liquid phase microextraction in hoUow fibers (aq/org) LPME3, three-phase liquid phase microextraction in hollow fibers (aq/org/aq). 

There are different variations of the MASX technique, including supported liquid membrane extraction (SLM), microporous membrane liquid-liquid extraction (MMLLE), polymeric membrane extraction (PME) and membrane extraction with a sorbent interface (MESI). These techniques will be briefly described below. 

Microporous membrane liquid- liquid extraction MMLLE Aq/org/org lonizable and neutral e.g. triazines in oil (38). 

Microporous Membrane Liquid-Liquid Extractiou (MMLLE)... 

Increasing the temperature of water extractions also increases the amount of matrix materials that are coextracted, especially for samples high in organic matter. Coextractants can reduce trapping efficiency and reproducibility on solid-phase traps. Using microporous membrane hquid-liquid extraction (MMLLE) in place of a sohd trap can more selectively trap PAHs from hot water extracts and minimize or eliminate sample cleanup. " The extraction solvent, cyclohexane, is immobilized in the pores of a polypropylene membrane where hquid-liquid mass transfer occurs. Limits of quantitation of about 1 for very small samples (5 to 10 mg) with an average... 

Two-phase liquid membrane extraction Microporous membrane Uquid-Uquid extraction MMLLE 16,1001... 

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