Preconcentration liquid microextraction

Fattahi, N., S. Samadi, Y. Assadi, and M. R. M. Hosseini. 2007. Solid-phase extraction combined with dispersive liquid-liquid microextraction-ultra preconcentration of chlorophenols in aqueous samples. J. Chromatogr. A 1169 63-69. 

Bosch Ojeda, C., Rojas, F.S. Separation and preconcentration by dispersive liquid-liquid microextraction procedure. Chromatographia 69, 1149-1159 (2009)... 

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... 

Einally, Ma and Cantwell" " developed liquid-liquid-liquid microextraction (LLLME) to achieve preconcentration and purification for polar analytes without the need for both solvent evaporation and analyte desorption. The compounds were extracted from aqueous samples (donor phase) into an organic phase, layered on the donor phase, then back extracted to the receiving phase, and suspended in the organic phase. After extraction, the microdrop was injected into the HPLC system directly for analysis " (Table 11.3). 

A method for preconcentration and separation of ultra-trace amounts of uranium from aqueous samples (mineral water, rivers, wells, springs, and seawater) based on combining SPE with liquid-liquid microextraction was described (Dadfarnia et al. 2013). The water samples were filtered (0.45 pm) and acidified fo pH 2 wifh... 

M. Shamsipur, M.M. Zahedi, G. De Filippo, V. Lippolis, Development of a novel flow injection liquid-liquid microextraction method for the on-line separation and preconcentration for determination of zinc(II) using 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a sensitive and selective fluorescent chemosensor, Talanta 85 (2011) 687—693. 

A central composite design was used to optimise the preconcentration of Cu " by dispersive liquid-liquid microextraction. 

Jain, R., M. K. Mudiam, A. Chauhan, C. Ratnasekhar, R. Murthy, and H. Khan. 2013. Simultaneous derivatization and preconcentration of parabens in food and other matrices by isobutyl chloroformate and dispersive liquid-liquid microextraction followed by gas chromatographic analysis. Food Ghent. 141(l) 436-443. 

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. 

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. 

Solid-Phase Microextraction Solid-phase microextraction (SPME) is a preconcentration technique based on the sorption of analytes present in a liquid phase or, more often, in a headspace gaseous phase, on a microbber coated with a chromatographic sorbent and incorporated in a microsyringe [15]. The analytes sorbed in the coating are transferred to a GC injector for thermal desorption. 

Solid-phase microextraction (SPME) — is a procedure originally developed for sample preconcentration in gas chromatography (GC). In this procedure a small-diameter fused silica optical fiber, coated with a liquid polymer phase such as poly(dimethylsiloxane), is immersed in an aqueous sample solution. The -> analytes partition into the polymer phase and are then thermally desorbed in the GC injector on the column. The same polymer coating is used as a stationary phase of capillary GC columns. The extraction is a non-exhaustive liquid-liquid extraction with the convenience that the organic phase is attached to the fiber. This fiber is contained in a syringe, which protects it and simplifies introduction of the fiber into a GC injector. Both uncoated and coated fibers with films of different GC stationary phases can be used. SPME can be successfully applied to the analysis of volatile chlorinated organic compounds, such as chlorinated organic solvents and substituted benzenes as well as nonvolatile chlorinated biphenyls. 

A related technique, called solid-phase microextraction, uses a fused silica fiber coated with a nonvolatile polymer to extract organic analytes directly from aqueous samples or from the headspace above the samples. The analyte partitions between the fiber and the liquid phase. The analytes are then desorbed thermally in the heated injector of a gas chromatograph (see Chapter 31). The extracting fiber is mounted in a holder that is much like an ordinary syringe. This technique combines sampling and sample preconcentration in a single step. 

Generally, preconcentration of pollutants from water samples and sample preparation steps are accomplished by extraction techniques based on enrichment of liquid phase (liquid/liquid extraction) or solid phase (solid/liquid extraction) ". Historically, liq-uid/liquid extraction (LEE) was used exclusively to enrich phenols from water samples. LEE is still used as a preconcentration step . However, there is an increasing tendency to replace LEE by solid phase extraction (SPE) and solid phase microextraction (SPME). Among the reasons for replacing LEE are foam formation, the large volume of organic solvents needed, the length of the analysis time and difficulties in the automation of LEE procedures. On the other hand, SPE requires incomparable smaller amounts of solvents (SPME requires no solvent at all) and can be easily automated . Finally, SPE and SPME are cheaper in comparison with LEE. 

A method for analysis of polar pesticides in wine by the use of automated in-tube SPME coupled with LC/ESI-MS was proposed (Wu et al., 2002). In-tube SPME is a microextraction and preconcentration technique that can be coupled on-line with high-performance liquid chromatography (HPLC), suitable for the analysis of less volatile and/ or thermally labile compounds. This technique uses a coated open tubular capillary as an SPME device and automated extraction. Using a polypyrrole coating, six phenylurea pesticides (diuron, fluometuron, linuron, monuron, neburon, siduron) and six carbamates (barban, car-baryl, chlorpropham, methiocarb, promecarb, propham) were analyzed in wine. Structures of compounds are reported in Fig. 9.4. Due to the high extraction efficiency of the fiber toward polar compounds, benzene compounds, and anionic species, LODs ranging between 0.01 and 1.2pg/L were achieved, even if the sample ethanol content affects the recoveries of analytes. 

SPE is an extraction method that uses a solid phase and a liquid phase to isolate and preconcentrate analytes of interest from a solution. The technique is based on partitioning of the analyte between the liquid phase and the extraction material (solid phase), with the mechanism of interaction depending on the extraction material. SPE is very popular, not only because it concentrates the sample, but can also be used to remove the analyte from interfering molecules if the interfering molecules do not show interactions with the SPE material. Chapter 27 of this book is devoted to SPE and its cousin, solid-phase microextraction. 

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. 

HFs have been used successfully for preconcentration in chemical analysis. One technique termed hollow-fiber liquid-phase microextraction (HF-LPME) involves filling the pores of an inert HF material (commonly polypropylene) with an organic phase containing a carrier in a similar way to the manufacturing of SLMs. The fiber is then dipped into an aqueous sample solution, and the analyte is transported across the HF to a small volume of receiver phase in the lumen of the HF that is subsequently analyzed [41,42]. 

Modern analytical techniques usually have sufficient sensitivity to determine the concentration of uranium in aqueous environmental samples and in most cases mass spectrometric techniques can also provide isotopic composition data. However, in some samples, especially where the precise content of minor uranium isotopes is required then preconcentration, separation, and purification can improve the accuracy of the measurement. Several methods have been developed for this purpose based on solid phase extraction (SPE), electro-analytical selective absorption techniques, liquid-extraction, ion-exchange and chromatographic columns, co-precipitation, and selective sorption. Other methods, like single-drop microextraction, are being developed and may serve for microanalysis (Jain and Verma 2011). Some of these techniques are discussed in the context of the specific sample preparation procedures throughout the book, so in this section only a few select methods will be discussed. 

Dadfamia, S., Shahani, A.M.H., Shakerian, F. et al. (2013). Comhination of sohd phase extraction and dispersive liquid-hquid microextraction for separation/preconcentration of ultra trace amounts of uranium prior to fiber optic-hnear array spectrophotometry determination,/. Hazard. Mater. 263, 670-676. doi 10.1016/j.hazmat.2013.10.028. 

For water samples, the most common extraction method is liquid-Uquid extraction using nonpolar solvent [46]. More recently other extraction methods have been employed. These indude the following micelle-mediated preconcentration (MMP) [47] solid-phase microextraction (SPME) [48], ACPE, [45] and sohd-phase extraction (SPE) [49]. 

Some remarkable applications for microemulsions constituted by ILs have been recently reported. For instance, aqueous IL microemulsions were used for hquid-liquid extraction. In particular, water/AOT/[C mim][PF ] system has been proved to entail selective extraction of hemoglobin from human whole blood [57] or to develop a synergic microextraction procedme for the preconcentration and determination of glucocorticoid hormones in water samples [58]. 

E. Ghasemi, N. M. Najafi, F. Raofie and A. Ghassempour, Simultaneous speciation and preconcentration of ultra traces of inorganic tellurium and selenium in environmental samples by hollow fiber liquid phase microextraction prior to electrothermal atomic absorption spectroscopy determination, J, Hazard, Mat., 2010, 181(1-3), 491-496. 

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. 

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