Extraction processes/schemes sequential

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). 

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. 

In order to study the composition and structure of pectins and their changes during ripening, storage and processing, various procedures have been developed for fractional extraction of pectins. A typical laboratory scheme for sequential extraction of pectin from plant cell wall materials is summarized in Figure 9.3. (Selvendran and O Neill, 1987 Voragen et al., 1995, Vierhuis et al., 2000). Not every step in the scheme is used by all of the researchers, and decisions depend on the source materials. 

Biochemists extract the contents of cells and separate the constituents based on differences In their chemical or physical properties, a process called fractionation. Of particular interest are proteins, the workhorses of many cellular processes. A typical fractionation scheme Involves use of various separation techniques In a sequential fashion. These separation techniques commonly are based on differences in the size of molecules or the electrical charge on their surface (Chapter 3). To purify a particular protein of interest, a purification scheme Is designed so that each step yields a preparation with fewer and fewer contaminating proteins, until finally only the protein of Interest remains (Figure 1-22). 

On the basis of the model of a heterogeneous membrane, it is possible to create a simulation scheme based on dynamic Monte Carlo computer simulations of the adsorption and desorption process on heterogeneous surfaces to extract the involved rate constants as a function of the calcium ion concentration. A simple simulation based on a modified, partly reversible, random sequential adsorption (RSA) algorithm provides very good accordance between experiment and measurement. Figure 8 schematically depicts the assumed model. 

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