Co-extraction of water

To date most of the work which has been done with supercritical fluid extraction has concentrated on the extraction of analytes from solid matrices or liquids supported on an inert solid carrier matrix. The extraction of aqueous matrices presents particular problems [276-278]. The co-extraction of water causes problems with restrictor plugging, column deterioration, and phase separation if a nonpolar solvent is used for sample collection. Also, carbon dioxide isay have limited extraction efficiency for many water soluble compounds. 

Oil extraction yield was not affected by moisture content in soybean (3-12%) [3] and dry-milled com germ (3.5-8%) [4]. Co-extraction of water was observed only during the final stages of extraction since oil is more soluble than water in SC-CO2 [1,5]. However, the amount of water in the oil extracts was not quantified. When Snyder et al. [3]... 

Law and Goerlitz in 1970 reported the effective removal of co-extractives from water using microcolumns of these three adsorbents for the analysis of chlorinated pesticides. The development of polystyrene resins such as XAD increased the ability to concentrate pesticide residues from water. Large volumes of sample water could be passed through an XAD resin and the pesticide would adsorb on the resin. Elution of the pesticide by an organic solvent such as methanol and subsequent cleanup by the adsorbent materials became the industry standard. 

The conditions in PHWE are typically harsh and, therefore, the method is not suitable for thermolabile compounds. Analytes may also react with each other or with the water molecules during the extraction. From an analytical point of view the most salient negative factors of SWE in the continuous mode are co-extraction of undesirable components of the matrix (usually polar components) and dilution of the analyte in the extract. This calls for a clean-up and concentration step prior to individual separation and detection of the target compounds. 

The extraction result is further influenced by the moisture content. For spices and herbs this concentration should be in general between 8 and 15 %. At higher values the water is extracted preferentially and/or the co-extraction of polar substances is at a low level. Low... 

The extraction solvent should be chosen such that the analyte is extracted with as little co-extraction of interfering substances as possible. Furthermore, choose a solvent that is compatible with the solid-phase extraction method that is being used. For example, samples that are high in fat are best homogenized with nonpolar solvents, such as hexane. The use of hexane as an extractant dictates normal-phase sorbents with silica, alumina, Florisil, or a CN sorbent. Samples with high water content are best homogenized with acids, bases, or polar solvents, such as methanol, acetonitrile, or acetone. The use of methanol or one of the water-miscible solvents suggests the use of reversed phase (C-18) and dilution of the extract with water or buffer. Thus, the choice of the extraction solvent will dictate the type of sorbent that will be used in SPE. 

Draisci and co-workers performed interesting research for the extraction of relatively polar analytes such as musk compounds in Italian fresh water fish (60) and corticosteroids in bovine liver (61). For musk components, alumina was utilized in the extraction cell to hinder co-extraction of lipids. The FFR values for these investigations were in the range 0.002 and 0.05, and in no case did they report problems with the presence of fet during the chromatographic analysis. For corticosteroids, a different concept was used, where fat was selectively extracted with pure hexane, followed by elution of the analytes in a second step. 

In contrast, a far wider range of extractants has been used in PIM studies. The extractant has the central role in the extraction process extractants are often synthesized with a target solute in mind and are designed to minimize co-extraction of non-target solutes. Ideally, extractants have low water solubility, are relatively cheap and react quickly with the solute of interest. Extractants should also be relatively inert to other species in the extraction system, although this is seldom fully achieved in practice. 

Inaba reports that AE-type nonionics may be isolated from environmental waters by toluene extraction (113). The presence of salts, as in sea water, will cause the co-extraction of anionic siufactants and other materials, so that a preliminary ion exchange step may be required prior to extraction. Liquid-liquid extraction with methylene chloride is generally applicable to isolation of ethoxylated surfactants from water (114). Liquid-liquid extraction with chloroform or methylene chloride was found to be equivalent to sublation in concentrating the NPE metabolite nonylphenoxyacetic acids from water. A pH of 2 is suitable for the extraction (35). Sublation was superior for analysis of sewage, since emulsion formation was minimized (115). 

R NHa + C.HjNCO = RNH CO NHC,Hj Traces of water will contaminate the product with diphenylurea (p. 336) if the solution is boiled hence the need for anhydrous conditions. i-Naphthylisocyanate reacts more slowly with water, and the i-naphthyl-urea derivative can often be obtained using a cold aqueous solution of an aliphatic amine it is particularly necessary in such cases to purify the product by recrystallisation from, or extraction with, boiling petroleum, leaving behind any insoluble di i-naphthylurea. Note that the amine must also be free from alcohols (p. 335) and phenols (p. 337). 

Larch Gum. Larch gum [37320-79-9] (larch arabinogalactan) is obtained by water extraction of the western larch tree, iLarix occidentalism the heartwood of which contains 5—35% on a dry wood basis. In the early 1960s, a countercurrent hot water extraction system was developed, and the gum was produced commercially by the St. Regis Paper Co. under the trade name Stractan. The potential production capacity of this gum is 10,000 t/yr based on the wood residues from the lumber industry. However, the product could not compete with gum arabic, and commercial production is now limited to small batches for a specific medical appHcation. 

The methyl a-hydroxyisobutyrate produced is dehydrated to MMA and water in two stages. First, the methyl a-hydroxyisobutyrate is vaporized and passed over a modified zeoHte catalyst at ca 240°C. A second reactor containing phosphoric acid is operated at ca 150°C to promote esterification of any methacrylic acid (MAA) formed in the first reactor (74,75). Methanol is co-fed to improve selectivity in each stage. Conversions of methyl a-hydroxyisobutyrate are greater than 99%, with selectivities to MMA near 96%. The reactor effluent is extracted with water to remove methanol and yield cmde MMA. This process has not yet been used on a commercial scale. 

The major advantage of the use of two-phase catalysis is the easy separation of the catalyst and product phases. FFowever, the co-miscibility of the product and catalyst phases can be problematic. An example is given by the biphasic aqueous hydro-formylation of ethene to propanal. Firstly, the propanal formed contains water, which has to be removed by distillation. This is difficult, due to formation of azeotropic mixtures. Secondly, a significant proportion of the rhodium catalyst is extracted from the reactor with the products, which prevents its efficient recovery. Nevertheless, the reaction of ethene itself in the water-based Rh-TPPTS system is fast. It is the high solubility of water in the propanal that prevents the application of the aqueous biphasic process [5]. 

Selective extraction experiments were then performed to see transference of some transition elements (Cu ", Ni ", Co ", and Fe " ) from the aqueous phase to the organic phase by the synthesized polymeric calixarenes. Phase-transfer studies in water-chloroform confirmed that polymer 2b and 3b were Fe ion-selective as was its monomer (1). Extraction of Fe " cation with 2b and 3b was observed to be maximum at pH 5.4. Only trace amounts of other metal cations such as Cu, Ni ", and Co " were transferred from the aqueous to the organic phase (Table 3). Furthermore, the extracted quantities of these cations remained unaffected with increasing pH. The effect of pH on the extraction of 3b was lower and 56% extraction was accomplished even at pH 2.2. The extraction experiments were also performed with calix[4]arene (1) the ratio was 8.4% at pH 2.2. The polymeric calix[4]arenes were selective to extract Fe " from an aqueous solution, which contained Cu +, Ni, Co ", and Fe " cations, and it was observed that the... 

A solution of 0.858 g (5.5 mmol) of 4-(1-methyl-l-butenyl)morpholine and 0.75 g (5.0 mmol) of ( )-(2-ni-troethenyl)benzene in 10 mL of diethyl ether is kept at r.t. for 4d. The solution is then evaporated and treated with a mixture of 13 mL of ethanol and 15 mL of 10% aq hydrochloric acid for 1 h at 25 C. The solution is extracted with CH2C12 and the organic phase is washed with aq Nall CO, then with water and dried over MgSO . Evaporation gives 1.04 g of an oil which is purified by column chromatography (silica gel. hexanc/cthyl acetate 10 1) to give the pure title compound as an oil yield 0.90g (77%). The diastereomeric ratio is determined by HPLC (methanol/water 4 1, reverse phase RP8) to be 93 7. 

Supercritical fluid extraction — During the past two decades, important progress was registered in the extraction of bioactive phytochemicals from plant or food matrices. Most of the work in this area focused on non-polar compounds (terpenoid flavors, hydrocarbons, carotenes) where a supercritical (SFE) method with CO2 offered high extraction efficiencies. Co-solvent systems combining CO2 with one or more modifiers extended the utility of the SFE-CO2 system to polar and even ionic compounds, e.g., supercritical water to extract polar compounds. This last technique claims the additional advantage of combining extraction and destruction of contaminants via the supercritical water oxidation process."... 

Production of the color involves centrifugal separation of the biomass, cell breakage, and extraction. Use of a salt solution rather than water as an extraction medium increases stability of the color during extraction. Methods for partial exclusion of the polysaccharide from the color extract in order to enhance resolubilization of the dried color were developed. These processes include either microfiltration or co-precipitation of the polysaccharide with an added positively charged polysaccha-... 

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