Extractants sequential extraction

In Procedure 11.10, step 1 is designed to extract soluble species, carbonates, and species on exchange sites. Step 2 is designed to extract reducible iron and magnesium oxyhydroxides. Step 3 extracts oxidizable organic matter and sulfides, while step 4 extracts any metals remaining after the completion of the previous extractions. Sequential extraction methods have also been used to extract and quantify the amounts of various arsenic species, primarily as As(III) and As(IV) in soil [21],... 

Extraction of hemiceUulose is a complex process that alters or degrades hemiceUulose in some manner (11,138). Alkaline reagents that break hydrogen bonds are the most effective solvents but they de-estetify and initiate -elimination reactions. Polar solvents such as DMSO and dimethylformamide are more specific and are used to extract partiaUy acetylated polymers from milled wood or holoceUulose (11,139). Solvent mixtures of increasing solvent power are employed in a sequential manner (138) and advantage is taken of the different behavior of various alkaUes and alkaline complexes under different experimental conditions of extraction, concentration, and temperature (4,140). Some sequences for these elaborate extraction schemes have been summarized (138,139) and an experimenter should optimize them for the material involved and the desired end product (102). 

Pitch. For the solvent analysis of pitch, a number of methods have been proposed. The solvents may be used sequentially or a fresh sample may be used with each solvent. Either the least or the most powerflil solvent may be used first. The ratio of solvent to pitch or pitch fraction and the temperature and time of extraction vary. 

The procedure of simultaneous extracting-spectrophotometric determination of nitrophenols in wastewater is proposed on the example of the analysis of mixtures of mono-, di-, and trinitrophenols. The procedure consists of extraction concentrating in an acid medium, and sequential back-extractions under various pH. Such procedures give possibility for isolation o-, m-, p-nitrophenols, a-, P-, y-dinitrophenols and trinitrophenol in separate groups. Simultaneous determination is carried out by summary light-absorption of nitrophenol-ions. The error of determination concentrations on maximum contaminant level in natural waters doesn t exceed 10%. The peculiarities of application of the sequential extractions under fixed pH were studied on the example of mixture of simplest phenols (phenol, o-, m-, />-cresols). The procedure of their determination is based on the extraction to carbon tetrachloride, subsequent back-extraction and spectrophotometric measurement of interaction products with diazo-p-nitroaniline. 

Despite the recent efforts for settling operational conditions for metal and metalloid fractionation, conventional batch sequential extraction schemes lack automation and are rather time consuming and laborious. Two additional main problems are the phase overlapping and possible re-adsorption of released elements. 

The behavior of elements (toxicity, bioavailability, and distribution) in the environment depends strongly on their chemical forms and type of binding and cannot be reliably predicted on the basis of the total concentration. In order to assess the mobility and reactivity of heavy metal (HM) species in solid samples (soils and sediments), batch sequential extraction procedures are used. HM are fractionated into operationally defined forms under the action of selective leaching reagents. 

In the present work it has been shown that on-line coupling of flowthrough fractionation in RCC with ICP-EAS detection enables not only the fast and efficient fractionation of trace elements (TE) in environmental solids to be achieved but allows real-time studies on the leaching process be made. A novel five-step sequential extraction scheme was tested in on-line mode. The optimal conditions for the fractionation were chosen. Investigating elution curves provides important information on the efficiency of the reagents used, the leaching time needed for the separation of each fraction, and the potential mobility of HM forms. 

Ricin (toxin from Castor bean Ricinus communis) [A chain 96638-28-7 B chain 96638-29-8] Mr -60,000, amorphous. Crude ricin, obtained by aqueous extraction and (NH4)2S04 pptn, was chromatographed on a galactosyl-Sepharose column with sequential elution of pure ricin. The second peak was due to ricin agglutinin. [Simmons and Russell Anal Biochem 146 206 1985.) Inhibitor of protein synthesis. EXTREMELY DANGEROUS, USE EXTREME CARE [instructions accompany product]. 

To reduce the quantity of ash in the extracts even further, steps were implemented using a sequential solids removal scheme that entailed a combination of centrifugation and filtration. Following extraction of the coal... 

Another point is related to the high acidity level of the final solution, which leads to certain limitations in the subsequent technological steps. Specifically, the high acidity of the initial solution eliminates any possibility for selective extraction, i.e. sequential separation of tantalum and then of niobium. Due to the high concentration of acids, only collective extraction (of tantalum and niobium together) can be performed, at least at the first step. In addition, extraction from a highly acidic solution might cause additional contamination of the final products with antimony and other related impurities. In order to reduce the level of contaminants in the initial solution, some special additives are applied prior to the liquid-liquid extraction. For instance, some mineral acids and base metals are added to the solution at certain temperatures to cause the precipitation of antimony [455 - 457]. 

The synthesis of key intermediate 12, in optically active form, commences with the resolution of racemic trans-2,3-epoxybutyric acid (27), a substance readily obtained by epoxidation of crotonic acid (26) (see Scheme 5). Treatment of racemic 27 with enantio-merically pure (S)-(-)-1 -a-napthylethylamine affords a 1 1 mixture of diastereomeric ammonium salts which can be resolved by recrystallization from absolute ethanol. Acidification of the resolved diastereomeric ammonium salts with methanesulfonic acid and extraction furnishes both epoxy acid enantiomers in eantiomerically pure form. Because the optical rotation and absolute configuration of one of the antipodes was known, the identity of enantiomerically pure epoxy acid, (+)-27, with the absolute configuration required for a synthesis of erythronolide B, could be confirmed. Sequential treatment of (+)-27 with ethyl chloroformate, excess sodium boro-hydride, and 2-methoxypropene with a trace of phosphorous oxychloride affords protected intermediate 28 in an overall yield of 76%. The action of ethyl chloroformate on carboxylic acid (+)-27 affords a mixed carbonic anhydride which is subsequently reduced by sodium borohydride to a primary alcohol. Protection of the primary hydroxyl group in the form of a mixed ketal is achieved easily with 2-methoxypropene and a catalytic amount of phosphorous oxychloride. 

A 17 amino acid long peptide sequentially related to opioid peptides in particular dynorphin A. OFQ/N is inactive at the 5, k, and p opioid receptors, but binds to its own NOP receptor (formerly ORL-1, for opioid receptor like-1). In contrast to opioid peptides, OFQ/N has no direct analgesic properties. OFQ/N is the first example for the discovery of a novel neurotransmitter from tissue extracts by using an orphan receptor as bait. Centrally administered in rodents, OFQ/N exerts anxiolytic properties. OFQ/N agonists and antagonists... 

The crude product was extracted sequentially with n-pentane and acetone, and analyzed by GPC and H1 NMR. 

Ruttenberg, K. C. (1992). Development of a sequential extraction method for different forms of phosphorus in marine sediments. Limnol. Oceanogr. 37, 1460-1482. 

Another approach to assess the partitioning of metals among the phases comprising natural particulate matter is to sequentially and selectively extract or dissolve portions of natural particulate matter. Based on the release of trace metals accompanying each step, associations between the trace metal and the extracted phase are inferred. Both of the above approaches have drawbacks, and at this time it is impossible to predict in advance how and to what extent metals and particulate matter will bond to one another in a natural system. Despite the uncertainties, empirical results can often be interpreted using the framework provided here. 

Babraj, J., Cuthbertson, D.J., Rickhuss, P., Meier-Augenstein, W., Smith, K, Bohe, J., Wolfe, R.R., Gibson, J.N., Adams, C. Rennie, M.J. (2002). Sequential extracts of human bone show differing collagen synthetic rates. Biochemical Society Transactions, Vol. 30, pp. 61-65. 

Thomas, R. R, Ure, A. M., Davidson, C. M., Littlejohn, D., Rauret, G., Rubio, R., and Lopez-Sanchez, J. F., Three-Stage Sequential Extraction Procedure for the Determination of Metal in River Sediments, Analytica Chimica Acta 286, 1994, 423 29. 

Because of their very complex chemical structures and heterogeneity, melanins are difficult to extract, separate, and characterize from tissues. Eumelanins are insoluble in water and organic solvents. They can be extracted from tissues with strong chemicals that are capable of removing lipids, proteins, and other tissue components but also lead to the formation of degradation products. Enzymatic procedures were developed for the isolation of eumelanins from mammalian hair and irises. The first step is sequential digestion with protease, proteinase K, and papaine in the presence... 

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