Extraction or Solids

When it is required to separate a solid from an impurity, it is desirable to carry out the extraction in a Soxhlet apparatus, a sketch of which is shown (Eig. 30). The substance to be extracted is placed in a paper thimble A which is set in position in the main Soxhlet tube, a loose plug of cotton wool being placed in the top of the thimble. The Soxhlet is attached to a flask B containing a small amount of a solvent the solvent chosen should be such that either the desired substance or the impurity is insoluble, or nearly so. A condenser is attached to the Soxhlet tube the ball condenser C shown in sketch is the most convenient. 

When the solvent is boiled, the vapour passes through opening D to the condenser, from which liquid drops back to the thimble. When this liquid reaches the top of the side tube E, it automatically syphons back into the flask B with the extracted matter in solution. The process is continuous. 

It is advisable to use a minimum quantity of solvent at the beginning and, if necessary, to add more solvent through the condenser. More rapid extraction can be brought about if the substance is intimately mixed with some inert substance, such as glass or sand. 

When the extraction is judged to be complete, the Soxhlet is removed and the substance crystallised from 

Funnels of the types shown in Fig. 31 are used. The liquids to be separated are run into the funnel, and after standing for some time the stopper at the top is removed and the more dense liquid is run off through the tap at the bottom. If the upper layer is required, it is poured out through the top of the funnel after running off the bottom layer this is to prevent contamination with the liquid in the stem and tap of the funnel. In all cases a funnel of convenient size should be chosen. 

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The analytes are typically extracted from the biological matrix using solvent extraction or solid phase extraction (SPE). Most analytes require some form of chemical derivatization prior to analysis by GC-MS techniques, whereas with LC-MS-MS no further treatment of the extract is required. The extracts obtained from urine are relatively dirty because of the many endogenous compounds that are present. It is for this reason that the very selective techniques of GC-MS-MS, GC-HRMS, or LC-MS-MS are required to detect some of the prohibited substances that have low detection levels. 

The synthesizer can produce as many as 200 compounds a week through single-step automated reactions that require minor cleanup routines or about 60 compounds a week through multistep reaction sequences that include labor-intensive liquid liquid extractions or solid-phase cleanup. 

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. 

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 common procedure for the analysis of nitrofuran metabolites involves hydrolysis of the protein-bound metabolites under acidic conditions followed by deriva-tization with 2-nitrobenzaldehyde (Eig. 7.5). After neutralization of the digest, solvent extraction is carried out with ethyl acetate. Residues are detected by LC-UV or LC-MS/MS In some cases an additional liquid-liquid extraction or solid-phase extraction step is applied to remove excessive matrix compounds. A broad overview of applied methods was published by Vass et al. in 2008. ... 

Simple dissolving or liquid-liquid extraction with immiscible solvents and pH control is often sufficient. For more complex samples, cleanup of extracts by column adsorption chromatography or a more modem method such as solid phase extraction, supercritical fluid extraction, or solid phase microextraction is usually applied. Cleanup is not as important in TLC because strongly sorbed matrix components that could irreversibly destroy a high-performance liquid chromatography column or carryover and be detected in later samples can be applied onto the plate if the subsequent development and detection of the analyte are not adversely affected. 

Among engineers, population balance concepts are of importance to aeronautical, chemical, civil (environmental), mechanical, and materials engineers. Chemical engineers have put population balances to the most diverse use. Applications have covered a wide range of dispersed phase systems, such as solid-liquid dispersions (although with incidental emphasis on crystallization systems), and gas-liquid, gas-solid, and liquid-liquid dispersions. Analyses of separation equipment such as for liquid-liquid extraction, or solid-liquid leaching and reactor equipment, such as bioreactors (microbial processes) fluidized bed reactors (catalytic reactions), and dispersed phase reactors (transfer across interface and reaction) all involve population balances. 

The purpose of Experiments 3 and 4 is to present methods for the TLC determination of pesticides. Experiment 3 describes procedures for the separation and detection of organochlorine (OCl), organophosphorus or organophosphate (OP), and Ai-methylcarbamate insecticides and metabolites (Sherma and Bloomer, 1977 Sherma et al., 1977, 1978 Sherma, 1978). Experiment 4 describes the quantitative TLC determination of three classes of herbicides after isolation from water by conventional separatory funnel extraction or solid-phase extraction (SPE) (Sherma, 1986c Sherma and Boymel, 1983). 

In food processing, the major objectives are sometimes achieved at the expense of some loss of recognised nutrients. However, in other cases, important nutrients may become available only after appropriate processing, since inhibitors or other interfering compounds may be destroyed or inactivated. Toxic factors can sometimes be destroyed by denaturation, as with enzymes, protease inhibitors and phyto-haemagglutinins. They can also be physically removed, for example by leaching, solvent extraction or solid classification methods, as in the removal of gossypol from cottonseed protein, or of phytate from cereals. 

Current official analytical methods for phenolic compound detection imply separation steps (liquid-liquid extraction or solid-phase extraction for liquid samples and Soxhlet extraction for solid samples) followed by chromatography using different detection devices, where they may require also a derivatization step. Unfortunately, these methods may require expensive and hazardous organic solvents, which are undesirable for health and disposal reasons in addition, the analysis is labour intensive and takes long time. Hence, there is a general trend to find alternatives that may also be utilizable for on-site analyses. 

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