Membrane liquid-phase microextraction

Lee, J. Lee, H.K. Rasmussen, K.E. Pedersen-Bjergaard, S. Environmental and bioanal3ftical applications of hollow fiber membrane liquid-phase microextraction A review. Anal. Chim. Acta 2008, 624, 253-268. 

Figure 4.9 Two modes of liquid phase microextraction, (a) Suspended drop method and (b) membrane loop method.

To simplify the above-mentioned MMLLE systems and, unlike the automated flowing MMLLE, the nonautomated, nonflowing design of MMLLE is simple to prepare manually and is an easy-to-use extraction procedure that is always done off-line prior to GC analysis. In this context, only a short piece of HF membrane is employed as an extraction device after the HF lumen and pores96 or only the pores97 have been filled with an appropriate organic solvent, the membrane is immediately immersed in the aqueous sample. The principle of this two-phase HF-MMLLE system is also called HF liquid-phase microextraction (HF-LPME) and will be briefly commented on in the next section. 

Hyotylainen, T. and M.-L. Riekkola. 2008. Sorbent- and liquid-phase microextraction techniques and membrane-assisted extraction in combination with gas chromatographic analysis A review. Anal. Chim. Acta 614 27-37. 

Bardstu, K.F., Ho, T.S., Rasmussen, K.E., Pedersen-Bjergaard, S. and Jonsson, J.A. (2007) Supported liquid membranes in hollow fiber liquid-phase microextraction (LPME) — Practical considerations in the three-phase mode. Journal of Separation Science, 30, 1364. 

In another type of membrane extraction devices, porous polypropylene hollow fibers are used, often in a disposable way, which minimizes carryover problems and reduces costs [26-33]. On the other hand, manual manipulations are needed, limiting the possibility for automation. With these devices, the extraction can be carried out in a static mode, either in large sample volumes, where the extraction is not intended to be complete, or in small volumes aiming for complete extraction. Usually, stirring is applied to increase the speed of mass transfer. Some typical practical arrangements are shown in Figure 12.2. This type of SLM extraction is often called hollow fiber liquid phase microextraction, or three-phase liquid phase microextraction or two-phase liquid phase microextraction but the terminology in this active field of research has not been settled. Also hollow fibers can be connected in flow systems [34,35]. 

FIGURE 12.2 Hollow-fiber devices for membrane extraction, (a) Hollow-fiber loops for equilibrium extraction redrawn after Liu et al. (From Liu, J.-F., Jbnsson, J.A., and Mayer, P., Anal. Chem., 77, 4800, 2005.) (b) Liquid-phase microextraction after Pedersen-Bjergaard and Rasmussen. (From Grpuhaug Halvorsen, T., Pedersen-Bjergaard, S., Reubsaet, J.L.E., and Rasmussen, K.E., J. Sep. ScL, 24, 615, 2001. With permission.) (c) Syringe-based hollow fiber LPME. (Erom Zhao, L. and Lee, H.K., Anal. Chem., 74, 2486, 2002. Copyright 2002 American Chemical Society. With permission.)... 

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). 

Recently, Psillakis et al. " have developed a liquid phase microextraction (LPME) technique using a hollow fiber membrane in conjunction with GC-MS for the extraction and analysis of phthalates. The resulting method was validated and compared with SPME. Both techniques showed comparable performance and were considered suitable for trace analysis of phthalates in water. 

Bardstu KF, Ho TS, Rasmussen KE, Pedersen-Bjergaard S, Jonsson jA. Supported hquid membranes in hollow fiber liquid-phase microextraction (LPME). Practical considerations in the 3-phase mode. J Sep Sci 2007 30 1364-1370. 

New progresses to establish LLE have been done in the past 10 years and is still under development. Examples of these include single-drop-liquid-phase microextraction (SD-LPME), LPME, and supported membrane extraction (SME). Single drop-LPME is based on a drop of organic solvent hanging at the end of a syringe needle. 

In liquid-phase microextraction (LPME), a liquid membrane is used to enrich and isolate analytes from a complex sample. The liquid membrane, which is immiscible with water and the sample matrix, is immobilized in the pores of a porous hollow fiber. Such a liquid membrane is referred to as a supported liquid membrane (S LM). Immobilization of the SLM is achieved by simply dipping the hollow fiber in an organic solvent allowing the pores to be filled. Figure 9.11 shows a schematic representation of LPME. 

LLE, liquid-liquid extraction MAE, microwave-assisted extraction SEE, solid-phase extraction SPME, solid-phase microextraction LPME, liquid-phase microextraction SOME, single-drop microextraction D-LLLME, dynamic liquid-liquid-liquid microextraction SEE, supercritical fluid extraction MIP, molecularly imprinted polymers sorbent SPMD, device for semipermeable membrane extraction PDMS, polydimethylsiloxane coated fiber PA, polyacrylate coated fiber CW-DMS, Carbowax-divinylbenzene fiber PDMS-DVB, polydimethylsiloxane divinylbenzene fiber CAR-PDMS, Carboxen-polydimethylsiloxane coated fiber DVB-CAR-PDMS, divinylbenzene Carboxen-polydimethylsiloxane coated fiber CW-TPR, Carbowax-template resin HS-SPME, headspace solid-phase microextraction MA-HS-SPME, microwave-assisted headspace-solid-phase microextraction HEM, porous hollow fiber membrane PEl-PPP, polydydroxylated polyparaphenylene. 

Yan, C.H. and Wu, H.F., A liquid-phase microextraction method, combining a dual gauge microsyringe with a hollow fiber membrane, for the determination of organochlorine pesticides in aqueous solution by gas chromatography/ion trap mass spectrometry. Rapid Commun. Mass Spectrom., 18, 3015, 2004. 

Different sample pretreatment operations include dilution, membrane-extraction (gas diffusion, dialysis), liquid-phase extraction techniques (liquid/liquid extraction, liquid-phase microextraction, single-drop microextraction) and solid reactors and packed columns aiming to facilitate online chemical derivatization, chromatographic separation of target species, removal of interfering matrix compounds, enzymatic assays, or determination of trace levels of analyte via sorptive preconcentration procedures (Marshall et al., 2003 Economou, 2005 Miro and Hansen, 2006 Theodoridis et al., 2007 McKelvie, 2008 Ruzicka, 2014). In this context, BIA and the LOV configurations are particularly useful. Acid-base titrations can also be automated using simple SIA manifolds and potentiometric (van Staden et al., 2002) or photometric (Kozak et al., 2011) detection. Typically, a zone of the sample to be titrated is sandwiched between two zones of titrant by aspiration. In the case of photometric detection, an additional zone of a suitable pH-sensitive colored indicator is aspirated. The stacked zones are delivered to the detector and the width of the peaks is monitored and related to the pH of the solution. 

In recent decades the development of preconcentration steps to be implemented prior to analytical determinations of trace level compounds has been explored in considerable depth. With a view to eliminating or at least minimising the use of organic solvents used in conventional liquid-liquid extraction, other methodologies have been developed, such as membrane extraction, solid-phase extraction, solid-phase microextraction, etc. 

The most widely employed techniques for the extraction of water samples for triazine compounds include liquid-liquid extraction (LLE), solid-phase extraction (SPE), and liquid-solid extraction (LSE). Although most reports involving SPE are off-line procedures, there is increasing interest and subsequently increasing numbers of reports regarding on-line SPE, the goal of which is to improve overall productivity and safety. To a lesser extent, solid-phase microextraction (SPME), supercritical fluid extraction (SEE), semi-permeable membrane device (SPMD), and molecularly imprinted polymer (MIP) techniques have been reported. 

Diffusive sampler Membrane extraction (MESI) Liquid-liquid extraction (LLE) Solid-phase extraction (SPE) SPE-PTV-GC Solid-phase microextraction (SPME) Headspace GC (SHS, DHS) Large-volume injection (LVI) Coupled HPLC-GC Membrane extraction (MESI) Difficult matrix introduction (DMI) Conventional solvent extraction methods 1 Pressurised solvent extraction methods Headspace GC (SHS, DHS) Thermal desorption (TD, DTD) Pyrolysis (Py) Photolysis Photon extraction (LD) Difficult matrix introduction (DMI)... 

In the past decade, several novel solvent-based microextraction techniques have been developed and applied to environmental and biological analysis. Notable approaches are single-drop microextraction,147 small volume extraction in levitated drops,148 flow injection extraction,149 150 and microporous membrane- or supported liquid membrane-based two- or three-phase microextraction.125 151-153 The two- and three-phase microextraction techniques utilizing supported liquid membranes deposited in the pores of hollow fiber membranes are the most explored for analytes of wide ranging polarities in biomatrices. This discussion will be limited to these protocols. 

In 2003, Smith reviewed newer sample preparation techniques, including pressurized liquid extraction, solid phase microextractions, membrane extraction, and headspace analysis. Most of these techniques aim to reduce the amount of sample and solvent required for efficient extraction. 

Sampling of these substances has been carried out following three approaches liquid absorbents [47], solid-phase microextraction (SPME) fibres [43] and filter substrates (mostly quartz fibre filters but also PTFE membranes [1, 42, 48, 49]). When filter substrates are used, atmospheric particles are collected over 24-h periods using high-volume (dichotomous or single-filter instruments [1, 48]), medium-volume or low-volume samplers (operated to ensure collection of sufficient aerosol mass [37, 50]). Samples were always stored at low temperamres (refrigerated or frozen) to ensure sample preservation. 

Yang et al. [47,48,53,54] developed a HWG sensing system for liquid and soil analyses based on an extractive polymer membrane coated onto the inside of the HWG. The polymer coating performs a solid-phase microextraction of the analyte from the headspace of the sample and preconcentrates the analyte prior to IR analysis. 

Lai B-W, Liu B-M, Mahk PK, Wu H-F. Combination of liquid-phase hollow fiber membrane microextraction with gas chromatography-negative chemical ionization mass spectrometry for the determination of dichlorophenol isomers in water and urine. Anal Chim Acta 2006 576(1) 61-66. 

One more trend that is worth mentioning is the miniaturization of sample preparation techniques. Solid phase microextraction is one good example of where very small samples are consumed and very small extracts are produced. Solid phase extractions can also be scaled down by reducing the bed volume or by use of coated membranes. Likewise liquid-liquid extractions can be scaled down conserving both sample and solvent. 

Another recent and new variant of membrane liquid extraction was introduced by Cantwell, and is known as liquid-liquid-liquid microextraction (LLLME). In this case three liquid phases are used — ai is the water sample where pH is adjusted to deionize the compounds, a2 the acceptor aqueous phase with pH adjusted to ionize the compounds and an organic liquid phase (o), 40 pi or 80 pi of -octane, which is layered over the donor phase. In this case no physical membrane is needed because the organic layer has this function. This modification is an appropriate application for preconcentration and purification for polar analytes in water samples such as amines... 

Bedendo GC, Carasek E. Simultaneous liquid-liquid microextraction and polypropylene microporous membrane solid-phase extraction of organochlorine pesticides in water, tomato and strawberry samples. J Chromatogr A 2010 1217 7-13. 

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