Liquid extraction from solid

Supercritical fluid extraction (SFE) and Solid Phase Extraction (SPE) are excellent alternatives to traditional extraction methods, with both being used independently for clean-up and/or analyte concentration prior to chromatographic analysis. While SFE has been demonstrated to be an excellent method for extracting organic compounds from solid matrices such as soil and food (36, 37), SPE has been mainly used for diluted liquid samples such as water, biological fluids and samples obtained after-liquid-liquid extraction on solid matrices (38, 39). The coupling of these two techniques (SPE-SFE) turns out to be an interesting method for the quantitative transfer... 

Modem refining technology uses tantalum and niobium fluoride compounds, and includes fluorination of raw material, separation and purification of tantalum and niobium by liquid-liquid extraction from such fluoride solutions. Preparation of additional products and by-products is also related to the treatment of fluoride solutions oxide production is based on the hydrolysis of tantalum and niobium fluorides into hydroxides production of potassium fluorotantalate (K - salt) requires the precipitation of fine crystals and finishing avoiding hydrolysis. Tantalum metal production is related to the chemistry of fluoride melts and is performed by sodium reduction of fluoride melts. Thus, the refining technology of tantalum and niobium involves work with tantalum and niobium fluoride compounds in solid, dissolved and molten states. 

Work is in progress to validate the MAE method, proposed for EPA, in a multi-laboratory evaluation study. Nothing similar has been reported for additives in polymeric matrices. Dean el al. [452] have reviewed microwave-assisted solvent extraction in environmental organic analysis. Chee et al. [468] have reported MAE of phthalate esters (DMP, DEP, DAP, DBP, BBP, DEHP) from marine sediments. The focus to date has centred on extractions from solid samples. However, recent experience suggests that MAE may also be important for extractions from liquids. 

Liquids can be extracted from solids by leaching. As the name implies, the soluble liquid contained in a solid is leached out by contacting the solid with a suitable solvent. A principal application of leaching is in the extraction of valuable oils from nuts and seeds such as, palm oil and rape seed oil. 

FIGURE 1.25 Principle of operation of solid-supported liquid-liquid extraction from aqueous or plasma samples. (Reproduced with permission from Varian, Inc.)... 

In Section 2.5, we described separation procedures in which analytes are extracted from solid samples via contact with liquid solvents that selectively dissolve the analyte and leave other components undissolved or unextracted. There are several methods by which analytes can be extracted from liquid matrices as well. 

The problems connected-with separation processes, units, and equipment are treated in the Sixth Chapter, focusing the reader s attention on high-pressure distillation and on dense-gas extraction from solids and liquids. 

Coal and Coal-Tar Hydrogenation. If paraffinic and olefinic liquids are extracted from solid fuel substances, the hydrogen content of the residual material is reduced even further, and the residues become more refractory. The yields of liquids so derivable are generally low, even when a significant fraction of the hydrogen is extractable. Thus production of fuel liquids from nonliquid fuel substances such as coal and coal tars may be enhanced only by the introduction of additional hydrogen in a synthesis process. The principal differences in the processes are from the modes in which hydrogen is introduced and the catalysts used. 

This chapter focuses on three widely used techniques for extraction of semivolatile organics from liquids liquid-liquid extraction (LLE), solid-phase extraction (SPE), and solid-phase microextraction (SPME). Other techniques may be useful in selected circumstances, but these three techniques have become the extraction methods of choice for research and commercial analytical laboratories. A fourth, recently introduced technique, stir bar sorptive extraction (SBSE), is also discussed. 

Sodium and potassium are extracted from solid samples by wet digestion or dry ashing followed by acid dissolution of residue, and are determined by flame AAS using an air—acetylene flame. Liquid samples are aspirated after dilution. 

Extraction procedures involve the removal of the analyte from a solid or liquid sample so that the analytical requirements can be achieved more satisfactorily than before, e.g. liquid-liquid extraction or solid-phase extraction. 

For extraction from solid samples, e.g., biological materials and homogenates (planf tissue, food), liquid extraction can be applied using for instance acetone, methanol, or acetonitrile. Often, extracts are filtered prior to injection to LC-MS. 

Supercritical Fluids (SFs) allow analytes to be extracted from solid samples, i.e., marine sediments, faster and more efficiently since they have lower viscosity and higher diffusivity than liquid solvents (56). CO2 is the most widely used supercritical fluid with or without a modifier, e.g. methanol and toluene. A very exhaustive discussion on the role of a modifier in the enhancement of the extraction efficiency was recently published (39). Few procedures have been described in the literature based on SFE of organic pollutants from environmental samples, including PCBs and PAHs (39, 41, 56-59). Generally, the extraction is performed... 

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. 

In addition to extraction from solids, supercritical fluids can be used to extract aromatic molecules from liquids. Senorans et al. have utilized carbon dioxide to extract high-quality brandy aroma using a countercurrent supercritical fluid extractor. The aroma quality is influenced by the extraction conditions. Medina and Martinez studied alcohol removal from beverages using supercritical carbon dioxide, to produce beverages with low-alcohol content but sufficient flavor, because of three key benefits 1) water and salts are not appreciably removed by the carbon dioxide 2) proteins and carbohydrates are not extracted or denatured and 3) there is a good control in the aroma recovery. The alcohol removal efficiency increases with the extraction pressure raffinate alcohol concentration can be reduced up to 3 wt.% at 250 bar and 40°C, from 6.2 wt.% in the feed. " ... 

FIGURE 11.1 A generalized flow scheme that indicates the fundamental elements of LC-MS-based bioanalysis. Abbreviations LLE = liquid-liquid extraction SPE = solid-phase extraction RAM = restricted-access media TEC = turbulent flow liquid chromatography API = atmospheric-pressure ionization APCI = atmospheric-pressure chemical ionization ESI = electrospray ionization SQMS = single-quadrupole mass spectrometry TQMS = triple-quadrupole mass spectrometry TOF = time-of-flight Q-TOF = quadrupole TOF. (Reprinted from Ackermann et al. [4], with permission from John Wiley Sons, Inc.)... 

SCFs may be used in the same way as other ordinary solvents taking into account their different properties and behaviors. Supercritical fluids can replace liquids solvents in many processes, such as extractions from solids (leaching), countercurrent multistage separations, chromatographic separations, and others, provided the solvent properties of the SCFs are adequate. 

Cleanup Device Samples. The percent dichloromethane extractables from solid and liquid samples collected by the gasifier cleanup devices are given in Table VI. A portion of the dichloromethane extractables from the Venturi scrubber decanter outlet water was fractionated on the Sephadex LH-20 column. The organic compounds in this sample eluted from the column primarily (approximately 80%) in Fraction 5. A portion of Fraction 5 was subfractionated into acidic, basic and neutral components. This resulted in 15 percent of the mass recovered in the acidic subfraction, 1.5 percent in the basic subfraction, 11 percent in the neutral subfraction and the remaining 72.5 percent being water soluble. Many nitrogen heterocycles were also found in the basic subfraction by 6C/MS analysis. 

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