Extraction back- from aqueous

The behavior of the system is very counterintuitive. The more extract-able component is relatively well behaved and a recovery of 99.4% is achieved in four stages. In contrast, the less extractable component behaves unusually. Its concentration increases in the aqueous phase between the first and the third stages. In the extract phase, it has a peak concentration in the extract from the fourth stage. Thus, the less extractable component circulates between the first and last stages, being squeezed out of the organic phase by the more extractable component, then being extracted back from the aqueous phase once the concentration of the more extractable component in the aqueous phase has fallen. 

The distribution coefficient for sulindac between phosphate buffer pH 7.0 and octanol at 25°C is 0.28. Sulindac can be extracted quantitatively from aqueous acidic media into the following organic solvents methylene chloride, chloroform, ethyl acetate and 3 volume % isoamyl alcohol in heptane. Sulindac can be back extracted into dilute alkali from these solvents. 

Cyclohexane, produced from the partial hydrogenation of benzene [71-43-2] also can be used as the feedstock for A manufacture. Such a process involves selective hydrogenation of benzene to cyclohexene, separation of the cyclohexene from unreacted benzene and cyclohexane (produced from over-hydrogenation of the benzene), and hydration of the cyclohexane to A. Asahi has obtained numerous patents on such a process and is in the process of commercialization (85,86). Indicated reaction conditions for the partial hydrogenation are 100—200°C and 1—10 kPa (0.1—1.5 psi) with a Ru or zinc-promoted Ru catalyst (87—90). The hydration reaction uses zeotites as catalyst in a two-phase system. Cyclohexene diffuses into an aqueous phase containing the zeotites and there is hydrated to A. The A then is extracted back into the organic phase. Reaction temperature is 90—150°C and reactor residence time is 30 min (91—94). 

A total volume of 2 L of hexane washes results, accompanied by the gradual precipitation of a yellow solid from the hexane washes. The acid-wash procedure frequently leads to emulsions and gunny yellow solid in both phases back-extraction of the "aqueous" layer with hexane may be necessary. 

In a method for the determination of copper, nickel, and vanadium in seawater, Shijo et al. [840] formed complexes with 2-(5-bromo-2 pyridylazo)-5-(N-propyl-N-sulfopropylamino) phenol and extracted these from the seawater with a xylene solution of capriquat. Following back-extraction into aqueous sodium perchlorate, the three metals were separated on a C is column by HPLC using a spectrophotometric detector. 

In order to be exploitable for extraction and purification of proteins/enzymes, RMs should exhibit two characteristic features. First, they should be capable of solubilizing proteins selectively. This protein uptake is referred to as forward extraction. Second, they should be able to release these proteins into aqueous phase so that a quantitative recovery of the purified protein can be obtained, which is referred to as back extraction. A schematic representation of protein solubilization in RMs from aqueous phase is shown in Fig. 2. In a number of recent publications, extraction and purification of proteins (both forward and back extraction) has been demonstrated using various reverse micellar systems [44,46-48]. In Table 2, exclusively various enzymes/proteins that are extracted using RMs as well as the stability and conformational studies of various enzymes in RMs are summarized. The studies revealed that the extraction process is generally controlled by various factors such as concentration and type of surfactant, pH and ionic strength of the aqueous phase, concentration and type of CO-surfactants, salts, charge of the protein, temperature, water content, size and shape of reverse micelles, etc. By manipulating these parameters selective sepa-... 

Using the described extraction system, we developed methods of amino acid recovery from pharmaceutical samples and fermentation broth. Amino acids were extracted efficiently from the diluted solution of fermentation broth into [C4Cilm][PFg] in the presence of DC18C6 and may be well back-extracted by the alkaline aqueous solution (pH > 9). These methods served as a basis for the corresponding analytical procedures. 

The handling and disposal problems associated with the use of liquid solvent extractors have resulted in increased attention to the separation and preconcentration of organic compounds in water by collection in synthetic polymers followed by elution with an organic solvent (2). For example, selective collection and concentration of organic bases on methylacrylic ester resin from dilute water samples have been reported (3). Such collection techniques are especially well-suited to flow-injection measurement techniques. In this study, ionizable organic analytes such as salicylic acid and 8-hydroxyquinoline (oxine) were extracted into a polymer and then back extracted by an aqueous solution. Amperometric measurement using a flow-injection technique was employed to monitor the process. 

Clarification of extracts can be accomplished with Carrez reagents (44). Purification has been performed by solid phase or partition. Wu et al. (47) absorbed saccharin onto ODS-4 cartridges and then eluted with methanol phosphate buffer. Puttemans et al. (28,50) extracted saccharin from soft drinks and yogurt by ion-pair extraction with tri-n-octylamine and back-extraction to an aqueous phase with perchlorate. Tereda and Sakabe (48) used cetrimide and Sep-Pak Cl8 in the cleanup of saccharin in coffee drink. The column was preconditioned with methanol, water, and 5 mM cetrimide. The sample, diluted in phosphate buffer pH 3.0 containing cetrimide was poured into the cartridge, washed with water, and eluted with acetonitrile water (1 1, v/v). Moriyasu et al. (40) added n-propylammonium bromide to the extract, passed it through a Bond Elut Cl 8 column, and eluted the sweetener with a mixture of methanol-water (4 6, v/v). The eluate was passed through a Bond Elut SAX column and washed with 0.5% phosphoric acid and water, and the sweetener was eluted with 0.3 N hydrochloric acid. 

The documented use of betalain pigments as food colorants dates back at least one century, when inferior red wines were colored with betalain-containing juices (e.g., red beet juice). This common practice was, however, soon prohibited, and the application of betalain colorants was widely replaced by artificial dyes, which displayed better stability, at a lower price, and with higher purity. But in recent years the interest in natural food colorants has been renewed, mainly because of consumers concerns about the safety of some artificial colorants, which may be hazardous to human health (234). As a result, the number of permitted artificial dyes has been markedly reduced, and new efforts had to be made to develop natural food colorants (235). However, current legislation restricts the application of betalain colorants to concentrates or powders (E 162) obtained from aqueous extracts of beets (211). 

An excellent method for the conversion of ether-soluble secondary alcohols to the corresponding ketones is by chromic acid oxidation in a two-phase ether-water system. The reaction is carried out at 25-30 °C with the stoichiometric quantity of chromic acid calculated on the basis of the above equation, and is exemplified by the preparation of octan-2-one and cyclohexanone (Expt 5.86). The success of this procedure is evidently due to the rapid formation of the chromate ester of the alcohol, which is then extracted into the aqueous phase, followed by formation of the ketone which is then extracted back into the ether phase and is thus protected from undesirable side reactions. 

Ban et al. reviewed the reduction properties of several salt-free reagents for Np(VI) and Pu(IV) to choose selective reductants that reduce only Np(VI) to Np(V) for separating Np from U and Pu in TBP by reductive back-extraction (165). Allylhydrazine was proposed as a candidate for selective Np(VI) reduction, and it was confirmed by a batch experiment that allylhydrazine reduced almost all Np(VI) to Np(V) and back-extracted Np from the organic phase (30% TBP/n-dodecane) to the aqueous phase (3 M HN03) within 10 minutes. A continuous countercurrent experiment using a miniature mixer-settler was carried out with allylhydrazine at room temperature. At least 91% of Np(VI) fed to the mixer-settler was selectively reduced to Np(V) and separated from U and Pu. 

Total dissolved MMHg can be analyzed by aqueous-phase ethylation after separating MMHg from the interfering chloride matrix by extraction with methylene chloride.88 For a 200-mL sample a detection limit of 0.075 pM is achieved. An alternative method for the simultaneous extraction of Hg(II) and MMHg in natural waters at fM levels is to extract both into toluene as dithiozonates after acidification of the water sample, followed by back extraction into an aqueous solution of Na2S and removal of H2S by purging with N2.89... 

The sample may be a large or a small volume of water, as determined by the instructor. A tracer is added to calculate the activity, as discussed below. The tracer and sample plutonium are prepared in the oxidation state Pu+4 by acid digestion with H202. The plutonium is then purified by an extraction cycle from 9N HC1 into TIOA. After extraction, the plutonium in TIOA is washed with HC1 and then back-extracted into an aqueous solution. 

---