Donor side, membrane 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. 

To improve the overall amount of analyte that is extracted, a flowing donor is often used i.e., the sample is pumped past the donor side of the membrane in a dynamic flow system. Also static systems with a stagnant donor are common, often with convective mixing by stirring. 

The transport of the substances from the feed solution to the strip side can be divided into the foUowing steps diffusion of substance S across the boundary aqueous layer in the feed (donor) phase, extraction (sorption) of substance on the donor/membrane phase interface, diffusion across the boundary layer on the feed (donor) side, convection transport in the liquid membrane zone, diffusion across the boundary layer on the strip (acceptor) phase of LM, re-extraction (desorption) on the membrane/strip phase... 

Little is known about the L-arabinofuranosyl transfer machinery. A gene in the genome of A. thaliana has been identified as a membrane-bound arabino-furanosyl transferase by its membrane-insertion sequence and the fact that mutants in the gene led to expression of mRNA, but phenotypes that were nonetheless defective in arabinan side-chains of their pectin. Attempts to use UDP-a-L-arabinopyranose as arabinofuranose donor in crude extracts, presumably in an attempt to uncover any mutase similar to UDP galactopyranose mutase (see Section 5.12.4), merely resulted in the incorporation of pyranose units into the arabinan. However, an enzyme using this donor has been shown to add the terminal arabinopyranosyl residue to the 3-position of the terminal arabinose of the 1,5-arabininan of rhamnogalacturonan 1. [By contrast, the o-arabinofuranosyl transfer machinery that produces the... 

Figure 10 Enrichment and separation setup for SLM extraction. A - peristaitic pump, B - membrane device with hoiiow fiber instaiied into fused siiica capiiiary, C - iniet on the donor side, D - washing iine used after enrichment, E - microinjection pump to transport the acceptor into ioop F, G - Cis packed capillary column, H - detector window, I - splitter unit, J - high pressure pump. (Adapted from Thordarson E, Palmarsdottir S, Mathiasson L, and Jonsson JA (1996) Sample preparation using a miniaturized supported liquid membrane device connected on-line to packed capillary liquid chromatography. Analytical Chemistry 68 2559-2563.)...

Membrane extraction (ME) techniques are a set of solvent-free extractions, which have gained popularity for VOC analysis in water (for applications see Table 23.8). The sample is in contact with one side of the membrane surface called feed or donor side. Analytes permeate selectively (according to their membrane affinity) through the membrane to the other side, called permeate or acceptor side, where they are retained by an acceptor phase. This process is called pertraction (permeation-extraction). 

Three physical realizations of SLM modules have been reported they are based on spiral, flat, and HF extraction units, as presented in Figure 4.3. Where a porous FS membrane is the liquid support in an automated flowing SLM configuration, flat and spiral modules are usually used, in which, respectively, a straight and a spiral machined groove is made in the inner two surfaces of the unit blocks.66,67 When the membrane support is sandwiched between the two unit blocks, donor and acceptor channels are formed on either side of the membrane. 

The principles and apphcations of SLM separation processes have been reviewed several times [4-7]. Briefly, in an SLM system an organic solvent is immobihzed in the pores of a porous polymer or inorganic support material by capillary forces, separating two aqueous solutions the feed (donor) and the strip (receiving, acceptor) phase (Fig. 3.1). The compounds are separated from the aqueous sample feed phase into an organic solvent immobilized in a support diffusing through the membrane phase, and then they are continuously back extracted to the other side of the membrane into the... 

Non-porous membranes can be used for extraction of polar and non-polar compounds from liquid samples using only minimal amount of organic solvent. A non-porous membrane is a liquid or a solid (e.g. polymeric) phase sandwiched between two other phases, usually aqueous but can also be gaseous (8). One of these two phases contains the components to be extracted, i.e. the donor phase. On the other side of the membrane is the acceptor phase, i.e. where the extracted components are collected. Usually, the membrane unit is made of two blocks of inert material with a machined groove in each. The membrane is placed in-between these blocks and clamped together, so that a channel (typically 10-1000... 

The SLM extraction technique can serve as an alternative sample preparation whenever dealing with difficult matrices and dirty samples, this being the case with many water samples [201,202]. The SLM extraction utilizes a porous hydrophobic membrane impregnated with a water-immiscible organic solvent. The membrane is placed between two blocks in which sample channels are formed on both sides of the membrane the donor and the acceptor. The analytes are extracted from the aqueous donor phase into the membrane and then back-extracted to the second aqueous phase, the acceptor. The process is normally driven by differences in pH between the two aqueous phases. By pumping the water sample in the donor and keeping the acceptor stagnant, an enrichment of the analytes in the acceptor is achieved. 

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