Liquid/solid extraction

In liquid-solid extraction (LSE) the analyte is extracted from the solid by a liquid, which is separated by filtration. Numerous extraction processes, representing various types and levels of energy, have been described steam distillation, simultaneous steam distillation-solvent extraction (SDE), passive hot solvent extraction, forced-flow leaching, (automated) Soxh-let extraction, shake-flask method, mechanically agitated reflux extraction, ultrasound-assisted extraction, y -ray-assisted extraction, microwave-assisted extraction (MAE), microwave-enhanced extraction (Soxwave ), microwave-assisted process (MAP ), gas-phase MAE, enhanced fluidity extraction, hot (subcritical) water extraction, supercritical fluid extraction (SFE), supercritical assisted liquid extraction, pressurised hot water extraction, enhanced solvent extraction (ESE ), solu-tion/precipitation, etc. The most successful systems are described in Sections 3.3.3-3.4.6. Other, less frequently 

Classical solvent extraction is a phase transfer of solute from the solid phase to solution. All analytical extractions from solid matrices undergo three processes  

Essentially, extraction of an analyte from one phase into a second phase is dependent upon two main factors solubility and equilibrium. The principle by which solvent extraction is successful is that like dissolves like . To identify which solvent performs best in which system, a number of chemical properties must be considered to determine the efficiency and success of an extraction [77]. Separation of a solute from solid, liquid or gaseous sample by using a suitable solvent is reliant upon the relationship described by Nemst s distribution or partition law. The traditional distribution or partition coefficient is defined as Kn = Cs/C, where Cs is the concentration of the solute in the solid and Ci is the species concentration in the liquid. A small Kd value stands for a more powerful solvent which is more likely to accumulate the target analyte. The shape of the partition isotherm can be used to deduce the behaviour of the solute in the extracting solvent. In theory, partitioning of the analyte between polymer and solvent prevents complete extraction. However, as the quantity of extracting solvent is much larger than that of the polymeric material, and the partition coefficients usually favour the solvent, in practice at equilibrium very low levels in the polymer will result. 

The efficacy and rate of the extraction process of additives from polymers are influenced by numerous factors including  

The extraction time has been observed to vary linearly with polymer density and decreases with smaller particle size [78,79]. The extraction time varies considerably for different solvents and additives. Small particle sizes are often essential to complete the extraction in reasonable times, and the solvents must be carefully selected to swell the polymer to dissolve the additives quantitatively. By powdering PP to 50 mesh size, 98 % extraction of BHT can be achieved by shaking at room temperature for 30 min with carbon disulfide. With isooctane the same recovery requires 125 min Santonox is extractable quantitatively with iso-octane only after 2000mm. The choice of solvent significantly influences the duration of the extraction. For example talc filled PP can be extracted in 72 h with chloroform, but needs only 24 h with THF [80]. pH plays a role in extracting weakly acidic and basic organic solutes, but is rarely addressed explicitly as a parameter. 

Most raw materials and many formulated products can be analysed without isolation of the surfactants. For some purposes, however, e.g. determination of molecular weight by titration, the surfactant must be isolated in a pure form. Liquid-solid extraction is useful for this purpose. It is also sometimes desirable to extract fatty acids, neutral fatty matter and/or weak fatty bases, either to determine them or to prevent interference with some other determination. Liquid-liquid extraction is appropriate for this. A special case is the analysis of structured bleaches, which may contain surfactants in strong hypochlorite. The bleach makes most analytical processes for the surfactants difficult or impossible, and the procedure given below is a useful first step. 

The sample size will depend on its active content, if known, and on what further analyses are envisaged. For an initial extraction of an unknown, 5 g is suitable. Caution organic solvents are mostly flammable or toxic or both, and appropriate precautions must be taken. 

Weigh a sample of the powder in a Soxhlet thimble, stand it in a beaker and dry to constant weight at 105°C. 

Protect the sample with a plug of cotton wool and place the thimble in a Soxhlet extractor. Attach a tared receiving flask and a reflux condenser. 

Slowly pour sufficient solvent (at least three times the volume of the extraction chamber) into the top of the condenser and allow it to syphon into the flask. 

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Emulsions Liquid-liquid Liquid-liquid-solid Gas-liquid-liquid Gas-liquid-liquid-solid Extraction... 

Extraction (sometimes called leaching) encompasses liquid-liquid as well as liquid-solid systems. Liquid-liquid extraction involves the transfer of solutes from one liquid phase into another liquid solvent it is normally conducted in mixer settlers, plate and agitated-tower contacting equipment, or packed or spray towers. Liquid-solid extraction, in which a liquid solvent is passed over a solid phase to remove some solute, is carried out in fixed-bed, moving-bed, or agitated-solid columns. 

S. Lacorte and D. Barcelo, Determination of parts per trillion levels of organophospho-rus pesticides in groundwater by automated on-line liquid- solid extraction followed by liquid chr omatography/atmospheric pressure chemical ionization mass spectrometry using positive and negative ion modes of operation . Anal. Chem. 68 2464- 2470 (1996). 

Castillo M, Domingues R, Alpendurada MF, et al. 1997. Persistence of selected pesticides and their phenolic transformation products in natural waters using off-line liquid solid extraction followed by liquid chromatographic techniques. Anal Chim Acta 353 133-142. 

Methods 508, 508.1, and 525.2 (EPA 1997a, 1997b, 1997c) are applicable to drinking water and ground-water and can determine a- and [3-endosulfan and endosulfan sulphate at concentrations as low as 7 ppt using liquid solid extraction (LSE) and GC/ECD. 

GC = gas chromatography ECD = electron capture detector EIA = enzyme-immunoassay GPC = gel permeation chromatography HPLC = high-performance liquid chromatography ITMS = ion trap mass spectrometer LSE = liquid solid extraction MS = mass spectrometry RSD = relative standard deviation SPE = solid phase extraction... 

EPA. 1997e. Methods and guidance for analysis of water. Method 508.1 Determination of chlorinated pesticides, herbicides, and organohalides by liquid-solid extraction and electron capture gas chromatography. U.S. Environmental Protection Agency, Washington, DC. EPA 821-C-97-001. 

The most widely employed techniques for the extraction of water samples for triazine compounds include liquid-liquid extraction (LLE), solid-phase extraction (SPE), and liquid-solid extraction (LSE). Although most reports involving SPE are off-line procedures, there is increasing interest and subsequently increasing numbers of reports regarding on-line SPE, the goal of which is to improve overall productivity and safety. To a lesser extent, solid-phase microextraction (SPME), supercritical fluid extraction (SEE), semi-permeable membrane device (SPMD), and molecularly imprinted polymer (MIP) techniques have been reported. 

Table 3.3 Essential conditions of liquid-solid extraction...

Rickies, R.N. Liquid-Solid Extraction, Chemical Engineering, Mar. 15, 1965, p. 157. 

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. 

Ultrasonic extraction is a well-known commercial method to increase mass transfer rate by cavitation forces. Bubbles in the liquid-solid extraction using UE can explosively collapse and produce localized pressure, improving the interaction between the intracellular substances and the solvent to facilitate the extraction of the phytochemical. 

Chiron S, Papilloud S, Haerdi W, Barcelo D (1995) Automated online liquid-solid extraction followed by liquid chromatography-high-flow pneumatically assisted electrospray mass-spectrometry for the determination of acidic herbicides in environmental waters. Anal Chem 67(9) 1637-1643... 

Ho JS, Tang PH, Eichelberger JW, et al. 1993. Determination of organic compounds in water by liquid solid extraction followed by supercritical fluid elution and capillary column gas chromatography/mass spectrometry. Denver, CO American Chemical Society, 313-315. 

Liquid-solid extraction followed by filtration or centrifugation... 

Determination of Organic Compounds in Drinking Water by Liquid- Solid Extraction and Capillary Column/Mass Spectrometry, USEPA Method 525.2, Rev. 2, USEPA, Cincinnati, OH, 1995. 

Technique selection Since you are a mass spectrometrist, you decide a liquid-solid extraction of the solid followed by MS analysis can identify impurities in the carbon. 

Define recrystallization, distillation, fractional distillation, extraction, liquid-liquid extraction, solvent extraction, countercurrent distribution, liquid-solid extraction, and chromatography. 

Liquid-solid extraction is the separation of a component of a solid sample through contact with a liquid extractant. 

Di Corcia A, Marchetti M. 1992. Method development for monitoring pesticides in environmental waters liquid-solid extraction followed by liquid chromatography. Environ Sci Technol 26(1 ) 66- 74... 

Saito, N., Ikushima, Y. and Goto, T. Bull. Chem. Soc. Japan 63 (1990) 1532-1534. Liquid-solid extraction of acetylacetone chelates with supercritical carbon dioxide. 

Puig D, Barcelo D. 1996. Comparison of different sorbent materials for on-line liquid-solid extraction followed by liquid chromatographic determination of priority phenolic compounds in environmental waters. J Chromatogr 733 371-381. 

Liquid-Solid Extraction and GC with an Electron Capture Detector (EPA/600/R-95-131)... 

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