Sequential extracting solutions

Cereal proteins when classified by the Osborne sequential extraction method yield four different classes albumins, which are water soluble, globulins, which are soluble in salt solutions, prolamins, which are soluble in alcohol-water mixtures, and glutelins, which are soluble in dilute acid or alkali. Chen and Bushuk added a fifth fraction by dividing the glutelin into two fractions, one soluble in dilute (0.05 m) acetic acid and the other insoluble in this reagent.5... 

In order to validate the hypothesis mentioned above, the Ni retention capacity of the Lac Tio waste rock was estimated using a batch sorption test performed on a fresh (C1) and weathered (C4) sample, followed by a 3-step Sequential Extraction Procedure (or SEP). The batch sorption test was done using a 10 mg/L Ni solution with an initial pH of 6, an ionic force adjusted to 0.05 M with NaN03 and with a liquid/solid ratio of 25. Some of the batch sorption results are presented in Figure 3. 

Fujitake N, Kusumoto A, Tsukamoto M, Kawahigashi M, Suzuki T, Otsuka H. Properties of soil humic substances in fractions obtained by sequential extraction with pyrophosphate solutions at different pHs I. Yield and particle size distribution. Soil Sci. Plant Nutr. 1998 44 253-260. 

To determine the various species and their concentrations in soil, many selective, semiselective, and sequential extraction methods have been developed. Species associated with various components in soil can be extracted with varying effectiveness (see Chapters 11 and 12). Thus, metal cations that are in solution, exchangeable, weakly held, or associated with carbonate and with... 

In operationally defined speciation the physical or chemical fractionation procedure applied to the sample defines the fraction isolated for measurement. For example, selective sequential extraction procedures are used to isolate metals associated with the water/acid soluble , exchangeable , reducible , oxidisable and residual fractions in a sediment. The reducible, oxidisable and residual fractions, for example, are often equated with the metals associated, bound or adsorbed in the iron/manganese oxyhydroxide, organic matter/sulfide and silicate phases, respectively. While this is often a convenient concept it must be emphasised that these associations are nominal and can be misleading. It is, therefore, sounder to regard the isolated fractions as defined by the operational procedure. Physical procedures such as the division of a solid sample into particle-size fractions or the isolation of a soil solution by filtration, centrifugation or dialysis are also examples of operational speciation. Indeed even the distinction between soluble and insoluble species in aquatic systems can be considered as operational speciation as it is based on the somewhat arbitrary definition of soluble as the ability to pass a 0.45/Am filter. 

This chapter considers methods of trace element speciation, and their application to soils, that involve selective chemical extraction techniques. It will be concerned firstly with extraction by single selective reagents and secondly with the development and application of sequential extraction procedures for soils and related materials. Sequential extraction procedures for sediments are discussed in depth in Chapter 11. Speciation in the soil solution and modelling aspects of its interaction with soil solid phases are comprehensively covered in Chapter 9 and will not be considered here. 

Variability between results obtained by different laboratories, particularly in Step 2 of the sequential extraction, had limited the number of analytes for which concentrations could be certified in CRM 601. A detailed investigation of this step was conducted, which revealed that small variations in the pH of the hydroxylammonium chloride extractant solution were the most important source of irreproducibility (Sahuquillo et al., 1999). Precision could also be improved by increasing the concentration of the reductant from 0.1 to 0.5 mol 1 1 NH2OH-HCl. See also 10.6.6. 

The other popular sequential extraction procedure is the protocol proposed by the Community Bureau of Reference, Commission of the European Community (known as the BCR protocol). The method was proposed on the basis of interlaboratory smdies undertaken in order to harmonize conditions for soil and sediment sample analysis. Based on the research data, in 1992 it was stated that application of EDTA or acetic acid solution is appropriate and sufficient for elimination of the bioaccessible fi action of metals from soil samples [62]. In the case of other samples, best results were achieved after application of a three-stage procedure with the following extractants ... 

Because the SEDEX scheme, like all sequential extraction schemes, is operationally defined, it is important to obtain corroborating evidence for the identity of the separately quantified sedimentary phosphorus reservoirs whenever possible. This can be accomplished by analyzing pore-water chemistry and other solid-phase components of the host sediments, and by linking depth profiles of various solutes and components to SEDEX phosphorus profiles. Some of the most elegant and comprehensive work of this type has been done by... 

In order to evaluate the maximum amount of metal that may be leached by urban sludge and the extracting action of different solutions on the same metal fraction, a future program based on a sequential extraction procedure on the same sludge sample must be carried out. 

At a constant temperature, the extraction of non-polar analytes is usually favoured by a low pressure, whereas that of polar analytes requires an increased one. This behaviour is used for class-selective extractions, an example of which is the sequential extraction of air particulates with supercritical CO,. Alkanes are extracted at 75 bar (45°C), whereas PAHs remain unextracted until the pressure is raised to 300 bar [26]. In some cases, an increase in pressure increases not only the solubility of the analyte but also its difiusivity. Such is the case with polymers, which absorb large amounts of COj under supercritical conditions, thereby swelling and facilitating diffusion of the solute. 

Another difficulty in the interpretation of sequential extraction data is that the availability of As from most stoichiometric As minerals does not fit neatly into one of the predefined chemical/mineralogical compartments, because it will be a function of the mineral solubility and dissolution kinetics under the chemical conditions of the extraction solution(s). For example, Voigt and Brantley (1997) determined that As in the mineral hoemesite (Mg3(As04)2. 8 H2O) was released during the exchangeable, carbonate, and Fe oxyhydroxide extraction steps before it was completely dissolved, leading to an overestimation of the fraction of As in ion-exchangeable sites and As associated with carbonate minerals. 

Prepare a block diagram of the modules involved in solving the material and energy balances for the extraction process used in a refinery for the production of normal paraffins shown in Fig. P5.18. Which additional modules not in Fig. 5.9a would you need Also indicate what streams might be cut for a sequential modular solution of the material and energy balances. 

Table 1 in Chapter 15 shows that water extracted 2.8% of an H+-ex-changed organic histosol as fulvic acids. When the residual soil was sequentially extracted, exhaustively, with aqueous solutions of sulfolane. 

Organic solvents have long been used for extraction and sequential extraction, which is fractionation of a sort (Flaig et al., 1975 Schnitzer, 1978). While the direct use of organic solvents in fractionation has not been widespread, nonetheless, the technique has received some attention. For instance, the separation of hymatomelanic acid from precipitated humic acid is obtained by extraction with ethanol (Oden, 1919). Ethanol has been used to bring about fractional precipitation by addition to alkaline solutions of humic acid (Kyuma, 1964 Kumada and Kawamura, 1968). There is no reason why other water-miscible solvents such as acetone and methanol should not be used in this way. Solvents that are highly immiscible with water (e.g., hexane and benzene) do not appear to remove any substantial fraction of humic substances. These are perhaps best used to remove nonhumic substances (such as fats and waxes) prior to extraction. However, recent work by Allen and MacCarthy (personal communication) has shown that more polar water-immiscible solvents, such as methyl isobutyl ketone and diethyl ether, can be used successfully to purify and fractionate humic substances. 

In addition, the overall content of TEs in extractable (mobile) forms can be estimated prior to SEP by a single-extraction procedure using electrolyte solutions, such as 1.0 mol HNO3 or 1.0 mol L HCl (Ladonin, 2002). If the contents of TEs obtained by the screening protocol are rather low, it might then be unreasonable to use a sequential extraction method. 

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