Conventional extraction

In order to maintain a definite contact area, soHd supports for the solvent membrane can be introduced (85). Those typically consist of hydrophobic polymeric films having pore sizes between 0.02 and 1 p.m. Figure 9c illustrates a hoUow fiber membrane where the feed solution flows around the fiber, the solvent—extractant phase is supported on the fiber wall, and the strip solution flows within the fiber. Supported membranes can also be used in conventional extraction where the supported phase is continuously fed and removed. This technique is known as dispersion-free solvent extraction (86,87). The level of research interest in membrane extraction is reflected by the fact that the 1990 International Solvent Extraction Conference (20) featured over 50 papers on this area, mainly as appHed to metals extraction. Pilot-scale studies of treatment of metal waste streams by Hquid membrane extraction have been reported (88). The developments in membrane technology have been reviewed (89). Despite the research interest and potential, membranes have yet to be appHed at an industrial production scale (90). 

The depressed prices of most metals in world markets in the 1980s and early 1990s have slowed the development of new metal extraction processes, although the search for improved extractants continues. There is a growing interest in the use of extraction for recovery of metals from effluent streams, for example the wastes from pickling plants and electroplating (qv) plants (276). Recovery of metals from Hquid effluent has been reviewed (277), and an AM-MAR concept for metal waste recovery has recentiy been reported (278). Possible appHcations exist in this area for Hquid membrane extraction (88) as weU as conventional extraction. Other schemes proposed for effluent treatment are a wetted fiber extraction process (279) and the use of two-phase aqueous extraction (280). 

The current state of analytical SPE was critically reviewed and no major changes of the technique have been observed. Overviews of the developments of the extraction technologies of secondary metabolites from plant materials refer to three types of conventional extraction techniques that involve the use of solvents, steam, or supercritical fluids. Each technique is described in detail with respect to typical processing parameters and recent developments. Eollowing the discussion of some technical and economic aspects of conventional and novel separation processes, a few general conclusions about the applicabilities of the different types of extraction techniques are drawn. ... 

Conventional extraction technologies. . 59 from polymer/additive ... 

More recently, some novel pressurised procedures for extraction of additives from polymers have been developed (Table 3.3). The principal objectives of all these techniques, such as SEE [89], MAE [90] and pressurised fluid extraction (PEE), is to replace the conventional extraction methods by shortening the extraction time, reduction in solvent use and automation. 

The advantages of automation of extraction under reflux versus manual sample preparation are well illustrated for HDPE/(Irganox 1010, Irgafos 168) (Table 3.7) [118]. No spikes were observed in the former case, as opposed to the latter. Boiling under reflux is considered by some [4] as the best all round conventional extraction method. 

Decreases the polarity of polar analytes (beneficial for conventional extraction)... 

Immunoaffinity procedures have also been developed to selectively extract corticosteroids from different sample matrices. Thus, Seymour et al. demonstrated the higher efficiency of the immunoaffinity methods compared with the conventional extraction procedures using organic solvents [177]. Immunosorbents have also been used for online procedures followed by HLPC-UV [178, 179], HPLC-APCI-MS [179,180], GC-MS [176,181], or capillary electrophoresis [182]. Poly(hydroxyethyl methacrylate) (HEMA) was evaluated as a support material for the anti-dexamethasone antibodies used in IAC. The online IAC-HPLC-MS allowed determination of dexamethasone and flumethasone in equine urine with LODs in the range 3-4 ng mL-1 [180]. The cross-reactivity values obtained in the ELISA and the recoveries of an IAC-HPLC procedure are presented in Table 7. Bagnati et al. developed an immunoaffinity extraction... 

Thermogravimetric methods such as pyrolysis gas chromatography-mass spectrometry have been used to characterize hydrocarbon sludges from polluted soils [10]. In combination with conventional extraction and supercritical fluid extraction followed by gas chromatography-mass spectrometry, over 100 constituents were identified in soil samples. Thermogravimetric analysis-mass spectrometric results distinguished between the release of a component by thermosorption and by pyrolysis. 

The most important advantage of cloud point extraction is that only small amounts of nonionic or zwitterionic surfactants are required and consequently the procedure is less costly and more environmentally benign than other conventional extraction techniques such as liquid-liquid extraction and solid liquid extraction [107,108]. Moreover, CPE offers the possibility of combining extraction and preconcentration in one step. 

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