Liquid extraction techniques

Contimious liquid extraction techniques are used when the sample volume is large, the distribution constant is small, or the rate of extraction is slow. The efficiency of extraction depends on many factors including the viscosity of the phases, the magnitude of the distribution constant, the relative phase volumes, the interfacial surface area, and the relative velocity of the phases. Numerous continuous extractors using llghter-than-water and heavier-than-water solvents vee been described [3,2 7,42,73,74]. Generally, either the ligi Pr or heavier density... 

Leoni [366] observed that in the extraction preconcentration of organochlo-rine insecticides and PCB s from surface and coastal waters in the presence of other pollutants such as oil, surface active substances, etc., the results obtained with an absorption column of Tenax-Celite are equivalent to those obtained with the continuous liquid-liquid extraction technique. For non-saline waters that contain solids in suspension that absorb pesticides, it may be necessary to filter the water before extraction with Tenax and then to extract the suspended solids separately. Analyses of river and estuarine sea waters, filtered before extraction, showed the effectiveness of Tenax, and the extracts obtained for pesticide analysis prove to be much less contaminated by interfering substances than corresponding extracts obtained by the liquid-liquid technique. Leoni et al. [365] showed that for the extraction of organic micro pollutants such as pesticides and aromatic polycyclic hydrocarbons from waters, the recoveries of these substances from unpolluted waters (mineral and potable waters) when added at the level of 1 xg/l averaged 90%. 

In the adsorption with Tenax alone satisfactory results were obtained, while in the presence of mineral oil a considerable proportion of the organophos-phorus pesticides (particularly Malathion and Parathion-methyl) was not adsorbed and was recovered in the filtered water. This drawback can be overcome by adding a layer of Celite 545 which, in order to prevent blocking of the column, is mixed with silanised glass wool plugs. A number of analyses of surface and estuarine sea waters were carried out by this modified Tenax column and simultaneously by the liquid-liquid extraction technique. To some of the samples taken, standard mixtures of pesticides were also added, each at the level of 1 xg/l (i.e., in concentration from 13 to 500 times higher than that usually found in the waters analysed). One recovery trial also specifically concerned polychlorobiphenyls. The results obtained in these tests show that the two extraction methods, when applied to surface waters that were not filtered before extraction, yielded very similar results for many insecticides, with the exception of compounds of the DDT series, for which discordant results were frequently obtained. 

The infrared method that has been used most frequently (EPA 418.1) is appropriate only for water samples. A separatory funnel liquid-liquid extraction technique is used to extiact hydrocarbons from the water. A method (EPA 5520D) using a Soxhlet extraction technique is suitable for sludge. This extiaction is frequently used to adapt the method (EPA 418.1) to soil samples. An infrared-based supercritical fluid extraction method for diesel range contamination (EPA 3560) is available. 

Oostdyk TS, Grob RL, Snyder JL, et al. 1994. Solid phase extraction of primary aromatic amines from aqueous samples comparison with liquid-liquid extraction techniques. J Environ Sci Health... 

The formation of two aqueous phases can be exploited in the recovery of proteins using liquid-liquid extraction techniques. Many factors contribute to the distribution of a protein between the two phases. Smaller solutes, such as amino acids, partition almost equally between the two phases, whereas larger proteins are more unevenly distributed. This effect becomes more pronounced as protein size increases. Increasing the polymer molecular weight in one phase decreases partitioning of the protein to that phase. The variation in surface properties between different proteins can be exploited to improve selectivity and yield. The use of more hydrophobic polymer systems, such as fatty acid esters of PEG added to the PEG phase, favors the distribution of more hydrophobic proteins to this phase. In Fig. 10.13, partition coefficients for several proteins in a dextran-PEG system are given [27]. 

Garcia C, Tiedra G, Ruano A, et al. 1992. Evaluation of the liquid-liquid extraction technique and application to the determination of volatile halo- organic compounds in chlorinated water. J Chromatogr 605 251 -255. 

The adaptation of supercritical fluid extraction (SFE) in routine residue and metabolism analysis as well as other extraction/separation laboratories and applications has been slow. This is despite the demonstrated feasibility of using SFE for the removal of sulfonylureas, phenylmethylureas and their metabolites from soil and plant materials (1-2), as well as widespread demonstrated use of supercritical fluid extraction for other applications (3-6). The reason for this is simple. Although automated, SFE extraction apparatus typically only analyzes a single sample at a time. The technique could not compete effectively with the productivity of an experienced technician performing many sample extractions simultaneously. In essence, with a one vessel automated supercritical fluid extractor, operator attendance is high and throughput is about the same or even less than current conventional liquid-liquid and solid-liquid extraction techniques. 

Ndungu, K. and L. Mathiasson. 2000. Microporous membrane liquid-liquid extraction technique combined with gas chromatography mass spectrometry for the determination of organotin compounds. Anal. Chim. Acta 404 319-328. 

Sandahl, M., L. Mathiasson, and J.A. Jonsson. 2000. Determination of thiophanate-methyl and its metabolites at trace level in spiked natural water using the supported liquid membrane extraction and the microporous membrane liquid-liquid extraction techniques combined on-line with high-performance liquid chromatography. J. Chromatogr. A 893 123-131. 

This procedure offers a number of advantages over conventional (static) HS and liquid extraction techniques for sample preparation. The major ones are the following ... 

The liquid extraction technique from ground solid samples may be used to isolate analytes from a solid. This extraction method is particularly useful when extracting analytes from dense materials, such as food, plant and animal tissues, or fats. 

An additional liquid extraction technique used to increase extraction... 

Hydrolysis versus halide complexation - studies using liquid-liquid extraction techniques... 

The processes developed initially were based essentially on liquid-liquid extraction techniques, but the chemical problems encountered in the treatment of irradiated Pu/Al targets (e.g. considerable interface fouling in the extractors and formation of stable emulsions) and the intensification of safety requirements led to use of extraction chromatographic techniques. 

The solubilisation of proteins and amino acids in organic solvents by reversed micelles provides a new method for the selective recovery, separation and concentration of bioproducts using liquid->liquid extraction techniques. Selectivity is affected by electrostatic interactions between the charged residues or moieties of the solute and the surfactant headgroups. These interactions are mediated by electrostatic screening as affected by solution ionic strength. The more hydrophobic the amino acid residue, the more favourable is the solubilisation of this residue in the partially structured water pool of the reversed micelle relative to the bulk, unstructured water phase. 

Reverse micelles are self-organized aggregates of amphiphilic molecules that provide a hydrophilic nano-scale droplet in apolar solvents. This polar core accommodates some hydrophilic biomolecules stabilized by a surfactant shell layer. Furthermore, reverse micellar solutions can extract proteins from aqueous bulk solutions through a water-oil interface. Such a liquid-liquid extraction technique is easy to scale up without a loss in resolution capability, complex equipment design, economic limitations and the impossibility of a continuous mode of operation. Therefore, reverse micellar protein extraction has great potential in facilitating large-scale protein recovery processes from fermentation broths for effective protein production. 

Soil, sediment, and dust samples were prepared in a similar way before analysis. After the pre-cleanup steps and homogenization, FRs were extracted from samples using different solid-liquid extraction techniques. The most commonly used technique was accelerated solvent extraction (ASE), which enables the fast extraction of samples using different solvents such as hexane and dichloromethane [98-100]. Other commonly used techniques for these samples were ultrawave-assisted extraction (UAE) [97], which also enabled quick extraction, and the more time-consuming but very efficient technique, Soxhlet extraction [96]. Some authors have also described less common techniques such as microSPE [95]. There is also information that many FRs that are no longer produced (mainly PCBs and PBDEs) are present in dusts, soils, and sediments in very high amounts, even 390 pg/g [98]. 

Castello G, Gerbino TC, Kanitz S. 1986. Sensitivity and linearity of headspace and liquid-liquid extraction techniques for gas chromatographic analysis of halocarbons in water. J Chromatogr 351 165-175. 

Otson R, Williams DT. 1981. Evaluation of a liquid-liquid extraction technique for water pollutants. J Chromatogr 212 187-198. 

More recently, a highly selective, sensitive, and rapid HPLC method has been developed and validated to quantify tadalafil in human plasma [44]. The tadalafil and internal standard (loratadine, I.S.) were extracted by liquid-liquid extraction technique followed by an aqueous back-extraction allowing injection of an aqueous solvent in the HPLC system. The chromatographic separation was performed on a reverse phase BDS Hypersil C18 column (250 mm x 4.6 mm, 5 pm. Thermo Separation Co., USA) with a mobile phase of acetonitrile and aqueous solution containing 0.012 M... 

The most difficult waste disposal problems arise from the effluents produced during the processing of spent nuclear fuel where liquid-liquid extraction techniques are used to recover fissile and fertile material from the various fission products. 

Accelerated solvent extraction, like many other recent techniques, has frequently been compared with well-established, other solid-liquid extraction techniques in order to assess its potential in various fields and identify its advantages and disadvantages relative to existing alternatives. 

Water. PCBs are non-polar compounds and consequently they are highly soluble in non-polar solvents this makes their extraction easier from water samples with nonpolar immiscible solvents. -Hexane and dichloromethane, or a mixture of them, are the most widely used solvents in liquid-liquid extraction techniques (1, 16, 29-31). Solid Phase Extraction (SPE) and elution with different mixtures of solvents (i.e., acetone/hexane/ dichloromethane) is a very attractive alternative to the liquid-liquid one (29, 32, 33). When large volumes of samples need to be collected, water can be pumped directly through a system containing an adsorbing material suitably supported, i.e., XAD-2, XAD-4, Tenax, C18, CI8-NH2, etc. It can be... 

Liquid extraction techniques using a variety of solvents have been reviewed (2,39) and the criteria for an ideal partition system for alcoholic beverages discussed by Clutton and Evans (40). These workers examined nine solvent systems for extraction of monoterpenes... 

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