Extraction strategies

Nonsolvents are unable to dissolve the substance in question. Their solubility parameters and hydrogen 

Whereas polymers of sufficiently high molecular weight may be soluble in the common solvents with some difficulty, network polymers do not dissolve, even at elevated temperature. They usually swell depending on the nature and cross-link density. Marcus [10] described the swelling of polystyrene cross-linked by divinylbenzene. 

For polymer/additive analysis complete dissolution is not a prerequisite. Rather, the solvent should at least swell the polymer by diffusion, which allows the physically blended additives to dissolve. True dissolution occurs predominantly when polymer chain lengths are small, on the order of 5000-10 000 Da. Solvent choice for dissolution or extraction should take into account restrictions imposed by further analysis steps (compatibility with chromatographic and/or spectroscopic requirements). When microwave extraction of additives from a polymer is followed by HPLC analysis, the solvent must be compatible with the HPLC mobile phase so that solvent exchange is not required before analysis. 

Quantitative or qualitative analysis of an analyte usually requires analyte isolation from matrix components, 

It is the difficult task of the analytical chemist to select the sample preparation technique best-suited for the problem at hand. The more tools there are in the toolkit, the larger the chances of finding a sample preparation technique that offers the desired characteristics. The goal of any extraction technique is to obtain extraction efficiency for the analyte which meets the analytical requirements in the shortest possible time. In some analytical procedures little sample handling is needed [46-49]. 

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In reality, finding a suitable solvent is not as easy as simply matching the polymer s solubility parameter (8 value). It is also important to take into account the effects of polymer crystallinity (as in the case of aPP and iPP, LDPE and HDPE). Because of their various chemical structures, it may be necessary to experiment with solvent, temperature, and time conditions to optimise the extraction strategy. 

The SP procedure of water-soluble vitamins from multivitamin tablets is particularly challenging due to the diverse analytes of varied hydrophobicities and pfC. Water-soluble vitamins (WSVs) include ascorbic acid (vitamin C), niacin, niacinamide, pyridoxine (vitamin B ), thiamine (vitamin Bj), folic acid, riboflavin (vitamin B2) and others. While most WSVs are highly water soluble, riboflavin is quite hydrophobic and insoluble in water. Folic acid is acidic while pyridoxine and thiamine are basic. In addition, ascorbic acid is light sensitive and easily oxidized. The extraction strategy employed was a two-step approach using mixed solvents of different polarity and acidity as follows ... 

Figure 30 Types of solvent extraction strategy in which V is the organic phase volume flowrate, y the concentration of solute in the organic feed, yp the concentration of solute in the organic product and y, the concentration in the organic phase leaving stage i Corresponding values for the aqueous phase are denoted by Va, xa, xp and xt respectively...

Sz. Nyiredy, Solid-liquid extraction strategy on the basis of solvent characterization , Chromatographia, 51 5288-5296 (2000). 

Dietz, Ch., J. Sanz, E. Sanz, R. Munos-Olivas, and C. Camara. 2007. Current perspectives in analyte extraction strategies for tin and arsenic speciation. J. Chromatogr. A 1153 114—129. 

Montes-Bayon, M. et al. Evaluation of different sample extraction strategies for selenium determination in selenium-emiched plants (Allium sativum and Brassica juncea) and Se speciation by HPLC-ICP-MS. Talanta 2006, 68, 1287-1293. 

The transfer of ions as pairs from one phase to a second is important in pre-analy tical extractive strategies. Ion-pair extraction of amines with bis-2-ethylhexylphosphate and derivatization with isobutyl chloroformate prior to GC-MS analysis was expedient for the simultaneous determination of aliphatic and aromatic amines in ambient air and airborne particulate matters [25]. The determination of 5-aminoimidazole-... 

Removal of extractables from an elastomer or plastic matrix can be accomplished by a variety of techniques, including solvent extraction (e.g., reflux and Soxhlet), supercritical fluid extraction, thermal evolution, etc. Jenke has thoroughly discussed and classified extraction strategies for container closure system components associated with a drug product leachables assessment. His discussion is based on two so-called directives paraphrased as follows ... 

The reader is encouraged to review Jenke s detailed discussion, nomenclature, and classification process for extraction strategies. Jenke has also published a... 

The algorithm G-REX uses crossover and mutation (see Figure 14.6), and the extraction strategy is based on genetic programming [106-109]. 

Fig. 10. Data extraction strategy An example of the octahedral region in the 5QMAS spectra of y-A2O3 overlaid with a grid of constant SOQE and lines. The SOQE spacing is 0.5 MHz and the chemical shift spacing is 2 ppm. Contours are drawn between 10 and 90% of the maximum spectral intensity. The box around the contour lines indicates 70% of the peak maximum. Values of 11-18 ppm and 2.2-4.1 MHz for and SOQE were determined, respectively. (Reprinted with permission from Goldbourt et Copyright (2003) American Chemical Society.)...

Rapid extraction, adaptability to a number of different solutes and solvents, the possibility of solvent recycling, enhancement in analytical selectivity and/or selectivity, ease of mechanisation and the possibility of exploiting different extraction strategies are favourable characteristics inherent to LLE [152], Drawbacks relate to operator protection and environmental safety requirements, the need for toxic, harmful, flammable and/or volatile organic solvents, the formation of undesirable emulsions, solvent costs for some highly selective procedures and the requirement for large volumes of sample, extractant or solvent [153]. 

In this section, SFE is compared with conventional extraction strategies such as solvent extraction and steam distillation. Conventional solvent extraction has quite a few disadvantages ... 

The use of SFE as a general extraction strategy for plant/microbial biomass is of particular importance in the extraction of unknown natural products, or... 

Purpose. To extract the active principle, an alkaloid, caffeine, from a native source, tea leaves. Caffeine is a metabolite (a product of the living system s biochemistry) found in a variety of plants. We wtU use ordinary tea bags as our source of raw material. This experiment illustrates an extraction technique often used to isolate water-soluble, weakly basic natural products from their biological source (see also Experiment [llA] for another extraction strategy). The isolation of caffeine win also give you the opportunity to use sublimation as a purification technique, since caffeine is a crystalline alkaloid that possesses sufficient vapor pressure to make it a good candidate for this procedure. In addition, the preparation of a derivative of caffeine, its 5-nitrosalicylate salt, will be carried out. This latter conversion takes advantage of the weakly basic character of this natural product. 

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