Liquid-phase microextraction extraction

More recently, a miniaturised version of liquid-liquid extraction has been developed, known as liquid-phase microextraction (LPME). Two main forms of this... 

H. T. Gronhaug, Pedersen-Bjergaard S, Rasmussen KE. Reduction of extraction times in liquid-phase microextraction. Journal of Chromatography B, Biomedical Sciences and Applications, 2001,760(2), 219-226. 

T. S. Ho, S. Pedersen-Bjergaard and K. E. Rasmussen, Recovery, enrichment and selectivity in liquid-phase microextraction comparison with conventional liquid-liquid extraction. Journal of Chromatography A, 2002,963(1-2), 3-17. 

Liu Jf, Chi Yg and Jiang Gb, Screening the extractability of some typical environmental pollutants by ionic liquids in liquid-phase microextraction. Journal of Separation Science, 2005, 28(1), 87-91. 

To enhance extraction efficiency in the SME system (also called single-drop microextraction [SDME]), He and Lee developed a procedure termed liquid-phase microextraction (LPME),89 which, in its static mode, resembles the SME system. 

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. 

Solvent Liquid/liquid extraction (LLE) Steam distillation/extraction (SDE) Solvent microextraction (SME) - SDME - LPME - DLLME Headspace-solvent-microextraction (HS-SME) - Headspace single-drop microextraction (HS-SDME) - Headspace liquid phase microextraction (HS-LPME) ... 

LPME Liquid-phase microextraction LLE with a minute amount of solvent, typically one microdrop, exposed at the tip of a microliter syringe, which is then withdrawn after extraction and injected into the GC Mostly GC-amenable analytes... 

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. 

LLE liquid-liquid extraction, SPE solid phase extraction, LPME liquid-phase microextraction, ESI electrospray ionization, APCI atmospheric pressure chemical ionization, SSI sonic spray ionization, Q quadrupole, QqQ triple quadrupole, TOF time-of-flight, IT ion trap, IS internal standard, CV coefficient of variation, MRE mean relative error, LOD limit of detection, LLOQ lower limit of quantification... 

Halvorsen TG, Pedersen-Bjergaard S, Reubsaet JLE et al (2003) Liquid-phase microextraction combined with liquid chromatography-mass spectrometry. Extraction from small volumes of biological samples. J Sep Sci 26 1520-1526... 

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). 

Pedersen-Bjergaard, S., Rasmussen, K. E. (2008). Liquid-phase microextraction with porous hoUow fibers, a miniaturized and highly flexible format for liquid-hquid extraction. J. Chromatogr. A, 1184, 132-42. 

Fig.l Headspace analysis and microextraction methods (here only the headspace mode is shown) used for the determination of fuel oxygenates, (a) Headspace analysis, (b) headspace solid-phase microextraction (HS-SPME) redrawn after [60], (c) solid-phase dynamic extraction (SPDE) redrawn after [61] and (d) liquid-phase microextraction (LPME) redrawn after [62]... 

Single drop extraction (SDE) or liquid-phase microextraction (LPME) is a recently developed microscale extraction method. In this method a single liquid drop is used as a collection phase. Small volumes of organic solvent (from 0.5 pi to 2.5 pi) are used. The collection phase must have a sufficiently high surface tension to form a drop which can be exposed to the analyte solution." When the extraction is finished, the single drop is injected into the GC. A scheme of such a device is shown in Eigure 2.8. 

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. 

Berhanu T, Megersa N, Solomon T, Jonsson JA. A novel equilibrium extraction technique employing hollow fiber liquid phase microextraction for trace enrichment of freely dissolved organophosphorus pesticides in environmental waters. Int J Environ Anal Chem 2008 88 933-945. 

Saleh A, Larsson E, Yamini Y, Jonsson jA. Hollow fiber liquid phase microextraction as a preconcentration and clean-up step after pressurized hot water extraction for the determination of non-steroidal anti-inflammatory drugs in sewage sludge. J Chromatogr A 2011 1218 1331-1339. 

LLE, liquid-liquid extraction SPE, solid-phase extraction LPME, liquid-phase microextraction S- -CD, sulfated / -cyclodextrin HP-/ -CD, hydroxypropyl- S-cyclodextrin SB- 8-CD, sulfobutyl-(3-cyclodextrin, CM- -CD, carboxymethyl- -cyclodextrin TM-/ -CD, trimethyl-/ -... 

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