Extraction of solids

APPARATUS FOR THE CONTINUOUS EXTRACTION OF SOLIDS OR LIQUIDS BY SOLVENTS... 

For extraction of solid materials with a solvent, a Soxhlet extractor is commonly used. This technique is applied, for example, in the alcohol extraction of dyes to free them from insoluble contaminants such as sodium chloride or sodium sulfate. 

Finally, the extraction of solid or semisolid masses into solvents can be carried out by use of a Soxhlet extractor (Fig. A3.1 lb). The. .ample is placed in a porous cup in the extractor. The boiling solvent condenses into the cup and accumulates until a siphon column is established in the adjacent tube. Then the saturated solvent returns to the boiling flask and fresh solvent distills again, repeating the process. 

This mode of chromatogram development is, in principle, almost identical with continuous development. The only feature that varies is the length of the developing path. In short bed-continuous development (SB/CD), this path is very short, typically equal to several centimeters [23-25]. This is the reason why this mode is preferentially applied for analytical separations. However, a similar technique is applied for zonal sample application and online extraction of solid samples, which are described in the following text. 

The procedure described earlier for sample preconcentration can be easily extended for the online extraction of solid samples, e.g., powdered plant materials. Horizontal conbguration of the chromatographic plate in the chamber facihtates this procedure, because the sample to be extracted is then placed on a carrier plate at the begiiming part of the adsorbent layer (or in the scrapped channel of the adsorbent layer), which should be directed upward [15,26]. The chamber is covered with a narrow plate, and the development is started with a snitable extracting solvent. In some cases, it is advantageous to put the narrow plate directly on the adsorbent layer to press the sample to be extracted. Extracted components are preconcentrated on the adsorbent layer at the end of the narrow plate, as shown in Fignre 6.26 [15]. 

APPARATUS FOR THE CONTINUOUS EXTRACTION OF SOLIDS OR LIQUIDS BY SOLVENTS Solids by solvents. The various forms of Soxhlet apparatus illustrated in Section 11,44 can be purchased with groimd glass joints. A simplified form, in which the fragile side tubes are absent, is shown in Fig. 77,58,1. The material to be extracted, if of granular form, may rest upon a sintered glass disc or upon a removable septum ... 

Apparatus for the continuous extraction of solids or liquids by solvents 222... 

Solid-phase sorbents are also used in a technique known as matrix solid-phase dispersion (MSPD). MSPD is a patented process first reported in 1989 for conducting the simultaneous disruption and extraction of solid and semi-solid samples. The technique is rapid and requires low volumes (ca. 10 mL) of solvents. One problem that has hindered further progress in pesticide residues analysis is the high ratio of sorbent to sample, typically 0.5-2 g of sorbent per 0.5 g of sample. This limits the sample size and creates problems with representative sub-sampling. It permits complete fractionation of the sample matrix components and also the ability to elute selectively a single compound or class of compounds from the same sample. Excellent reviews of the practical and theoretical aspects of MSPD " and applications in food analysis were presented by Barker.Torres et reported the use of MSPD for the... 

Fig. 39. Plot of the amount extracted (%) of solid nucleobase (C, A, G, T) into solutions of receptors of type 38 in (I) CD3CN and (II) (CD3)2CO. Reproduced with permission from Ref. (136). Copyright 1993, American Chemical Society.

Figure 3.3 Apparatus for intermittent extraction of solids 1, boiler vessel 2, extraction vessel 3, cooler 4, heating coil 5, transformer 6, contact-block 7, timer. Reproduced by permission of DSM Research, Geleen...

There are a number of procedures described in the literature dealing with the extraction of emerging contaminants from solid matrices. For extractions of solid samples, Soxhlet is widely accepted as a robust liquid-solid extraction technique. 

Studies designed to improve the determination of environmental contaminants will continue to provide refinements and improvements in the determination of acrylonitrile. The current high level of activity in supercritical fluid extraction of solid and semisolid samples should yield improved recoveries and sensitivities for the determination of acrylonitrile in solid wastes, and the compound should be amenable to supercritical fluid chromatographic analysis. Immunoassay analysis is another area of intense current activity from which substantial advances in the determination of acrylonitrile in environmental samples can be anticipated (Vanderlaan et al. 1988). 

Figure 12.6. Soxhlet setup for extraction of solid samples.

Solid waste or oil waste (EPA Method 9013) Extraction of solid component with water at pH >10 and hexane Titrimetric or colorimetric detection (soluble cyanides) No data 60-90 (solid) 88-92 (oil) EPA1992e... 

Solvent extraction reduction is most frequently performed mainly in connection with the extraction of solid and biological samples by liquid partition. Extractions are typically accomplished using a Soxhlet apparatus that provides the benefits of multiple extractions. By repeated distillation and condensation of the solvent, the apparatus allows multiple extractions using the same (small) volume of solvent. Soxhlet extraction has been a standard method for many decades, and it is often the method against which other extraction methods are measured and verified [14]. 

SPE methods with different cartridge packings have been employed for the pre-concentration and clean up of sulfonated azo dyes from waters and soil extracts [110,111], The extraction of solid samples has been carried ont by sonication or Soxhlet extraction and the extracts treated like the water samples. C18 cartridges and columns [111] were used followed by the elution with aqueous organic solvents in the presence of TEA with recovery yields always greater than 65% [93,111], Higher recoveries have been obtained by using C18 columns, pre-conditioned with an ammonium acetate buffer and elnted with methanol [111], The use of styrene-divinylbenzene [93,112], as well as of cross-linked polymeric sorbents with sulfonate functions, was shown to be suitable in the SPE of the more polar componnds [111],... 

Extraction of solids with high-pressure fluid in mixed-flow... 

Lugue de Castro, M.D. and Garcia-Ayuso, L.E. 1998. Soxhlet extraction of solid materials An outdated technique with a promising innovative future. Anal. Chim. Acta 369 1-10. 

There are not a lot of detailed published procedures for the homogenization and extraction of solid foods. This is not surprising, since there is such a wide array of distinct sample matrices. No single procedure can be expected to work for all sample types. Development of homogeniza-tion/extraction procedures must necessarily be on a case-by-case basis. It is important for the investigator to verify the efficiency of the procedure with respect to the overall recoveries afforded and the kinetics of the extraction. 

Figure 5. Apparatus used for the dynamic headspace extraction of solid foods. (1) Carrier gas (He) inlet, (2) belt transmission, (3) glass cylinder (99 x 8.5 cm), (4) Tenax trap (16 x 1.8 cm), (5) thermostat [adapted from reference 55],...

Chesler, S. "The Round Robin Test Materials and a Summary of the Results," Consortium on Automated Analytical Laboratory Systems, 2nd CAALS Workshop on Supercritical Fluid Extraction of Solid Environmental Samples, November 8, 1991, NIST, Gaithersburg, MD. 

ASTM D-5369. Standard Practice for Extraction of Solid Waste Samples for Chemical Analysis Using Soxhlet Extraction. 

Extraction of solid samples Homogenization extractions Sonication extractions Microwave assisted extractions Soxhlet extractions Accelerated solvent extractions Supercritical fluid extractions Extraction of liquid samples Liquid-liquid extractions Solid phase extractions (SPE)... 

Nanosized ZnO particles are prepared by hydrolysis-condensation at moderate temperature (from 20 to 70°C) [27-29] of zinc-acetate precursors [30] in ethanolic medium. Besides the determination of local order around Zn and of the particle sizes during the nanosized ZnO preparation, the motivation of the combined investigation was also to clarify the occurrence of a Zn-based hydroxy double salt phase, Zn5(0H)8(0C0CH3)2.2H20 (labeled hereafter Zn-HDS) observed as final solid mixed with ZnO and zinc acetate phases [29]. In particular, we were interested in determining whether the formation of the Zn-HDS phase was concomitant to the ZnO formation or arose from the reaction of ZnO with zinc acetate precursors during ageing of the colloidal suspension before extraction of solids. 

A serious test of mixture equations of state is shown to be their application for prediction of solubility of solutes in supercritical fluids (JJ. ). In the present report, we apply the Redl ich-Kwong and the Peng-Robinson equations of state for supercritical fluid extraction of solids and study the effect of choosing different mixing rules on prediction of solubility of solids in supercritical fluids -Figures 1-5. 

The turn-key multipurpose high pressure pilot unit shown in picture 1 can be used for the continuous extraction of liquid products in a column with structured packings and for the batch extraction of solids in a extraction vessel. It is assembled using the following proven basic modules (see also figure 1) ... 

As reported in a lot of reviews, extractions with supercritical solvents have a very promising commercial potential. Until now the commercialization is mainly restricted to batchwise extraction of solids with carbon dioxide (e g. decaffeination of coffee and tea, extraction of hop). Laboratory experiments and operation of small-scale pilot plants gave favourable economic values for continuous extraction of liquids with C02 and other gases. Only a few extractions with C02 or C HS are performed already on a small industrial scale. For research purposes and product development a new high pressure counter-current extraction plant was erected. To get greater amounts of product the explosionproof plant was constructed in pilot scale using a special modular concept and an effective visual control system. 

The partitioning of a substance between two liquid phases (multistage partitioning, partition chromatography) and the extraction of solids require similar properties of a solvent [50-55]. When a substance has to be partitioned, a solvent system with limited miscibility of the components is required in order that the substance dissolves to a different extent in the two phases. The greater the chemical differences between any two solvents, the more limited their miscibility. Other requirements that the solvent system must fulfil are, inter alia, a favorable partition coefficient (the average partition coefficient of the component mixture should be between ca. 0.2 and 5), as high a separation... 

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