Composition of the Extracts

Identification of the molecular species within coal extracts is an important step in determining not only the composition of the extracts but also the effectiveness of the extraction process. 

There are many examples reported in the scientific literature in which the properties of coal extracts resemble the properties of the original coal. Whether or not this is fortuitous or to be anticipated because of the nature of the technique or because of a true resemblance has been the subject of many lengthy debates. The matter of true resemblance between coal extracts and the original coal is still not resolved, but for the present context it should be noted that when consideration is given to the comparative analyses of extracts and residues, it is essential to distinguish between low-temperature extractions and high-temperature extractions whereby (in the latter case) the extract may be substantially richer in hydrogen. 

Size exclusion chromatography (SEC) is a powerful method for determining molecular weight distributions of mixtures. Because coal fractions usually contain both polar and nonpolar molecules, interpretation of SEC data is difficult and subject to error. Advantages and problems with tetrahy-drofuran (THE), A(-methyl-2-pyrrolidone, and pyridine have been observed (Lafleur and Nakagawa, 1989) but some investigators continue to employ these solvents, thereby ignoring any pitfalls. 

Among the methods that have the possibility for identification of specific compounds in solvent extracts, GC/MS has been the most studied. However, a disadvantage to the use of nonpolar solvents is that potentially soluble molecules may not be accessible to the solvent and their absence may bias the conclusions drawn. For this purpose, mixed solvents such as benzene/methanol should be 

To avoid the problems associated with the nse of mixed solvents, chromatographic fractionation of pyridine extracts is often used to isolate fractions that can be analyzed by mass spectroscopy. In the usual methods, elution from a silica gel colnmn or alnmina column will prodnce increasingly polar extract fractions that may be farther fractionated on other supports for specific analyses. 

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The result obtained by GC-MS, with the same SPME conditions, from the black thick balm of a crocodile mummy (sample 1400, Musee Guimet, Lyon, France) is presented in Figure 10.11. The composition of the extract is close to that of sample 1998 but phenolic compounds were not detected. The GC-MS chromatogram obtained with the same substance after acid methanolysis and silylation is presented in Figure 10.12. Except for the sesquiterpenoids eluted between 10 min and 22 min, the observed compounds originate from a beeswax. The biomarkers of this substance are hexadecanoic acids hydroxylated in position 14 or 15 and long chain hydrocarbons, acids and alcohols eluted between 50 min and 90 min. Diterpenoid or triterpenoid resin components are not observed. 

From Figure 13b, the composition of the extract from stage 1, I i i, is ... 

Some of the above-mentioned limitations, but not all, can be overcome by making an extract of the soil and determining the elemental composition of the extract. This approach can eliminate or minimize problems associated with XRF analysis being limited to particle surface [34,35]. 

It was concluded from the data that MAE can be applied for the efficient extraction of carotenoid pigments from paprika powder, however the amount and composition of the extracted pigment depends considerably on the composition of the extracting agent [30],... 

Since most APIs have some aqueous solubility, extraction is typically performed at room temperature with aqueous or a mixture of aqueous and organic media.Extraction can be performed in one step with a single solvent or in multiple steps executed sequentially with different solvents. The extraction solvent must be able to solubilize the API and be compatible with the HPLC mobile phase for the final analysis. The pH, buffer concentration and organic solvent composition of the extraction... 

Solvent Swelling and Extraction, The residue samples were extracted with pyridine at the boiling point to obtain the amount and composition of the extract. A portion of the dried, extracted solids was swelled in pyridine in order to estimate the density of crosslinks introduced by the preliquefaction process. The solvent swelling measurements were carried out according to the method of Green et al. (30,31). 

Flavan-3-ols (catechins, proanthocyanidins, and condensed tannins) can often be extracted directly with water. However, the composition of the extract does vary with the solvent — whether water, methanol, ethanol, acetone, or ethyl acetate. For example, it is claimed that methanol is the best solvent for catechins and 70% acetone for procyanidins. ... 

A simulation experiment is performed to validate the method, which can be formulated in algorithms. The applicability of the algorithms to practice is tested by means of the performance of extraction experiments for a group of sulphonamides. The response (partition coefficient) is modelled versus the composition of the extraction liquid. The models are used to predict the criteria within the entire mixture space. 

The most economical procedure for a liquid-liquid extraction would be a single step extraction, since extraction procedures including several steps with the same or with different solvents are laborious and economically disadvantageous. Optimisation of extraction of more than one solute, which give different selective interactions (different response surfaces in the same mixture space), may require several extraction steps with different optimal extraction solvents or separate analysis of each analyte. However, procedures can be used, which select a composition of the extraction liquid that provides satisfactory partition coefficients or extraction yields for all solutes to be extracted. 

In an optimisation procedure involving the minimal partition coefficient, the minimal partition coefficient is calculated using all compositions of the extraction liquid (all possible combinations of x, X2 and within the mixture space). The highest value calculated for this minimal partition coefficient (the maximal minimal partition coefficient) is the optimal value and hence the composition where the partition coefficient of the worst extractable substance is highest. 

With the use of the regression models a partition coefficient for each compound and a selectivity for each pair of substances can be predicted in each composition of the extraction liquid within the factor space. Figure 7.1 demonstrates the response surfaces of the partition coefficients of two compounds i and j in a binary extraction liquid i.e. an extraction liquid composed of two solvents). The compositions where the partition coefficients of i and j are optimal are represented by O, and 0, respectively. The optimal compositions with regard to the selectivity is represented by 0 . Two situations are given. 

In the left part of the figure the shapes of the response surfaces of the partition coefficients are dissimilar for both compounds. The maximal minimal partition coefficient is found in 0 . 0 also generates the maximal minimal selectivity, which is equal to unity in this case (a, is represented by the minimum value of a,j and afa. The selectivity varies largely with extraction liquid composition. Composition 0 yields a high ratio of P, and Pj, but this ratio is very sensitive to small fluctuations in the composition of the extraction liquid a fraction of extraction liquid component one (x,)... 

In the right part of Figure 7.1, the maximal minimal partition coefficient is found in O,. Here, the composition where the ratio of the partition coefficients of compounds i and j reaches its optimum, Oo, is also the composition that gives a robust selectivity. Optima with respect to maximal partition coefficients of both compounds are obtained with different compositions. The response surfaces are not completely parallel. Little variation in the composition of the extraction liquid does influence... 

The composition of the extraction liquid is very important for the magnitude of the partition coefficient of a solute. Several quantities have been studied to describe solvent properties. Snyder [20,21] grouped the relative selectivity of solvents into solvent selectivity classification groups, each group formed according to proton donating, proton accepting and dipole interaction properties. 

COMPOSITIONS OF THE EXTRACTION LIQUIDS USED FOR THE ALGORITHM VALIDATION EXPERIMENT AND FOR THE MODELLING OF THE EXTRACTION OF A NUMBER OF SULPHONAMIDES... 

Vanilla extract (vanilla oleoresin) is produced by extraction of the pods of Vanilla planifolia G. Jacks, or V. tahitensis Moore (Orchidaceae) with a polar solvent (e.g., methanol, ethanol, or acetone, which may also contain water). The composition of the extract depends on the type and amount of solvent used. Generally, the percentage of vanillin in the extract (yield 25-30%) is 3-4 times higher than that in the pods [807c, 807d]. 

A reconstructed ion chromatogram (GC-MS) containing extractable contaminants isolated from a typical lot of foam is shown in Figure 4. The qualitative composition of the extractable contaminants was provided by GC-MS. Contaminant profiles were identical for each of the two solvent systems employed, methylene chloride (1003 ) and ethyl ether/hexane (5/95). The contaminant chemistry shown here and again in Figure 5 in several instances is consistent with the manufacturing process data shown in the box, most notably the presence of residual toluene diisocyanate (starting materials, see Scheme II) and an aliphatic amine (possible reaction catalyst). 

The composition of the extracts will vary and is dependent on coal rank and the solvent employed for the extraction. Nevertheless, the composition of the extracts can be reported in the form of four or five major fractions as deduced by adsorption chromatography (Speight, 2001, 2002). 

The IR spectrum of the aqueous extract Is shown In Figure 6. Note the >C=0 absorption peak at about 1700 cm-. The exact composition of the extract Is not known. Note, however, that (1) the extract absorbs at about 265 nm In the UV, Indicating carbonyl species (2) the extract absorbs at about 1700 cm-l In the IR, Indicating either carbonyl or carboxyl species and (3) that the extract Is addle. It Is likely, then, that this peak may be assigned to various low-molecular-weight degradation products that may account for the acidity of the extract. It also should be noted that this spectrum Is essentially the same as that reported by Kleinert (18. 19) for the aqueous extract of naturally and artificially aged linen. 

Thus, a positive value of AD shows synergism and a negative value of the same indicates antagonism, and its magnitude is a measure of the extent of these effects. The variation of AD, as a function of different experimental parameters, is the sole basis on which the composition of the extracted species, responsible for synergism, is usually obtained. The value of AD depends on many experimental parameters and, frequently AD approaches D(a+B), when (DA + DB) is negligible relative to D(A+B). 

A number of methods are used for establishing the composition of the extracted metal species and for the calculation of the relevant equilibrium constants. The application of these methods is illustrated below using the HA-B extractant combinations. A similar approach can be used for other systems as well with suitable modifications dictated by any additional equilibria that may be involved in them. 

From these results and from the free amino acid compositions of the extracts, they regarded amino acids, chiefly glutamic acid and glycine, as the main contributors to the taste of these crustaceans. 

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