Static solvent extraction

Supercritical fluid extraction can be performed in a static system with the attainment of a steady-state equilibrium or in a continuous leaching mode (dynamic mode) for which equilibrium is unlikely to be obtained (257,260). In most instances the dynamic approach has been preferred, although the selection of the method probably depends just as much on the properties of the matrix as those of the analyte. The potential for saturation of a component with limited solubility in a static solvent pool may hinder complete recovery of the analyte. In a dynamic system, the analyte is continuously exposed to a fresh stream of solvent, increasing the rate of extraction from the matrix. In a static systea... 

Freitas S, Walz A, Merkle HP, Gander B (2003) Solvent extraction employing a static micromixer a simple, robust and versatile technology for the microencapsulation of proteins. J Microencapsulation 20 67-85 FZK Press release 13 (2005) http //www.fzk.de/fzk/idcplg IdcService=FZK node=2374 document=ID 050927. Cited 6 July 2005 Gavriilidis A, Angeli P, Cao E, Yeong KK, Wan YSS (2002) Trans IChemE 80/A 3... 

The most common technique for the radiochemical determination of complexing constants utilizes partition methods which are based on reactions between two phases under static or dynamic conditions (chromatography). Partition methods offer the advantages of simplicity and rapidity and are amenable to a broad selection of phase compositions and arrangements. One of the most reliable partition methods, especially useful for measuring 0 , is solvent extraction. It is best applied to systems which exhibit compound formation (11). 

Cobalt(II) chloride was dissolved in poly(amide acid)/ N,N-dimethylacetamide solutions. Solvent cast films were prepared and subsequently dried and cured in static air, forced air or inert gas ovens with controlled humidity. The resulting structures contain a near surface gradient of cobalt oxide and also residual cobalt(II) chloride dispersed throughout the bul)c of the film. Two properties of these films, surface resistivity and bullc thermal stability, are substantially reduced compared with the nonmodified condensation polyimide films. In an attempt to recover the high thermal stability characteristic of polyimide films but retain the decreased surface resistivity solvent extraction of the thermally imidized films has been pursued. 

Schoenmakers et al. [72] analyzed two representative commercial rubbers by gas chromatography-mass spectrometry (GC-MS) and detected more than 100 different compounds. The rubbers, mixtures of isobutylene and isoprene, were analyzed after being cryogenically grinded and submitted to two different extraction procedures a Sohxlet extraction with a series of solvents and a static-headspace extraction, which entailed placing the sample in a 20-mL sealed vial in an oven at 110°C for 5,20, or 50 min. Although these are not the conditions to which pharmaceutical products are submitted, the results may give an idea of which compounds could be expected from these materials. Residual monomers, isobutylene in the dimeric or tetrameric form, and compounds derived from the scission of the polymeric chain were found in the extracts. Table 32 presents an overview of the nature of the compounds identified in the headspace and Soxhlet extracts of the polymers. While the liquid-phase extraction was able to extract less volatile compounds, the headspace technique was able to show the presence of compounds with low molecular mass... 

Because SPME extracts compounds selectively, the response to each compound must be calibrated for quantification. A specific compound can be quantified by using three GC peak area values from solvent injection, static headspace (gas-tight syringe), and SPME. The solvent injection is used to quantify the GC peak area response of a compound. This is used to quantify the amount of the compound in the headspace. The SPME response is then compared to the quantified static headspace extraction. These three stages are necessary because a known gas-phase concentration of most aroma compounds at low levels is not readily produced. A headspace of unknown concentration is thus produced and quantified with the solvent injection. Calibration must be conducted independently for each fiber and must include each compound to be quantified. 

For a compound to contribute to the aroma of a food, the compound must have odor activity and volatilize from the food into the head-space at a concentration above its detection threshold. Since aroma compounds are usually present in a headspace at levels too low to be detected by GC, headspace extraction also requires concentration. SPME headspace extraction lends itself to aroma analysis, since it selectively extracts and concentrates compounds in the headspace. Some other methods used for sample preparation for aroma analysis include purge-and-trap or porous polymer extraction, static headspace extraction, and solvent extraction. A comparison of these methods is summarized in Table Gl.6.2. 

Phospholipid-derived fatty acids are often used to identify bacteria by capillary GC analysis after liquid solvent extraction, concentration steps, and chemical derivatization to their methyl esters. Our initial investigations attempted to extract the intact phospholipids, but no significant recoveries were achieved using pure C02. Even if SFE conditions were developed that could extract intact phospholipids, an additional derivatization step would be required before GC analysis of the fatty acid components. For these reasons, chemical derivatization/SFE was investigated in an effort to eliminate the lengthy conventional liquid solvent extractions as well as to combine (and shorten) the extraction and derivatization steps. The derivatization/SFE procedure was performed on samples of whole bacteria using 0.5 mL of 1.5% TMPA in methanol. The static derivatization step was performed for 10 minutes at 80°C and 400 atm C02, followed by dynamic SFE for 15 minutes at a flow rate of ca. 0.5 mL/min of the pressurized C02. Extracts were collected in ca. 3 mL of methanol and immediately analyzed by capillary GC without any further sample preparation. 

Hubert et al. [101] state that accelerated solvent extraction compared to alternatives such as Soxhlet extraction, steam distillation, microwave extraction, ultrasonic extraction and, in some cases, supercritical fluid extraction is an exceptionally effective extraction technique. Hubert et al. [ 101 ] studied the effect of operating variables such as choice of solvent and temperature on the solvent extraction of a range of accelerated persistent organic pollutants in soil, including chlorobenzenes, HCH isomers, DDX, polychlorobiphenyl cogeners and polycyclic aromatic hydrocarbons. Temperatures ofbetween 20 and 180 °C were studied. The optimum extraction conditions use two extraction steps at 80 and 140 °C with static cycles (extraction time 35 minutes) using toluene as a solvent and at a pressure of 15 MPa. 

Analytical methods for the analysis of volatile compounds in the environment have been extensively reviewed.85 87 159 160 The volatility of this class of compounds—industrial solvents, emissions from the petrochemical industry and from combustion engines—suggests that GC should be used for their determination. Solvent-free sample preparation techniques, such as P T (dynamic HS), static HS, and SPME or SBSE, in which the analytes are isolated from the aqueous matrix and simultaneously preconcentrated, are preferred. They also have the advantage that extraction solvents that could interfere with early-eluting, volatile analytes are avoided. If solvent extraction of volatile compounds... 

There are many techniques available for the preparation of volatile analytes prior to instrumental analysis. In this chapter the major techniques, leading primarily to gas chromatographic analysis, have been explored. It is seen that the classical techniques purge and trap, static headspace extraction, and liquid-liquid extraction still have important roles in chemical analysis of all sample types. New techniques, such as SPME and membrane extraction, offer promise as the needs for automation, field sampling, and solvent reduction increase. For whatever problems may confront the analyst, there is an appropriate technique available the main analytical difficulty may lie in choosing the most appropriate one. 

Among the static partition techniques, solvent extraction was the most used for heavy elements studies. For instance RJ. Silva et al. [12] using a mixture... 

Static pressurized hot solvent extraction (SPHSE), which shall henceforward be referred to as accelerated solvent extraction (ASE) for the reasons stated above, is the less flexible PHSE mode in terms of alteration or coupling to other techniques but is so far the more widely used — in fact, it accounts for over 65% of the PHSE publications reported since 1994. This is mainly the result of the sole commercially available extractor (the Dionex 200 model) implementing the static mode alone and also of the large number of studies conducted by different or even the same authors on the same analytes in the same matrices, which have therefore contributed little or nothing new in this area [58-63]. 

Accelerated solvent extraction as implemented in commercial equipment is basically discrete in nature, so it is rarely coupled to other operations of the analytical process. In fact, only in two reported applications was the static mode coupled on-line to other operations such as chromatographic separation, preconcentration and detection. Both used custom extractors as the compact design of the commercial models precluded their adaptation. 

Phenol, a common priority pollutant, was extracted from two environmental matrices, soil and water, using near critical and supercritical carbon dioxide. The primary objective of this study was to determine the distribution of the contaminant between the soil or water and the supercritical phase, and the effect of soil moisture and co-solvents on the distribution coefficients. Static equilibrium extractions were performed on dry and wetted soil contaminated with 1 wt.% phenol and on water containing 6.8 wt.% phenol. Supercritical carbon dioxide (with and without en-trainers) was chosen as the solvent for the study. An appropriate entrainer for dry soil extractions (methanol) ffiffered from that found for aqueous extractions (benzene). However, soil moisture was found to have a significant impact on the effectiveness of en-trainers for soil extractions of phenol. Entrainers appropriate for extracting wetted soil were found to be the same as those advantageous for aqueous extractions. Benzene was also extracted from dry and wetted soil to investigate the extractability of a hydrophobic compound. 

The processing equipment used to conduct solvent extraction of metals is the same as that used in conventional liquid-liquid extraction.1 1 The most common choices have been mixer-settlers, columns with agitated internals, and static mixers. Some advantages and disadvantages of several classes of equipment are summarized in Table 8.5-1. Many of the practical aspects of equipment selection are diicussed by Pratt and Hanson5 and by Ritcey and Ashbrook. ... 

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