Extractions, multi-step

Environmental monitoring of chloroacetanilides requires methods that have the capability to distinguish between complex arrays of related residues. The two example methods detailed here for water monitoring meet this requirement, but the method for metabolites requires sophisticated mass spectral equipment for the detection of directly injected water samples. In the near term, some laboratories may need to modify this method by incorporation of an extraction/concentration step, such as SPE, that would allow for concentration of the sample, so that a less sensitive and, correspondingly, less expensive, mass spectral detector can be used. However, laboratories may want to consider purchasing a sensitive instrument rather than spending time on additional wet chemistry procedures. In the future, sensitive instrumentation may be less expensive and available to all laboratories. Work is under way to expand the existing multi-residue methods to include determination of additional chloroacetanilides and their metabolites in both water and soil samples. 

Gibson, M.J. and Farmer, J.G., Multi-step sequential chemical extraction of heavy metals from urban soils, Environ. Poll. (Ser. B), 11, 117, 1986. 

For PBDE analyses, the complexity of sludge matrix implies the use of multi-step purification methods. Sludge extracts contain relatively large amounts of elemental sulfur, which would disturb the GC analysis, and must be removed. 

Several authors reported the use of ionic liquids containing protonic acid in catalysis (118-120). For example, strong Bronsted acidity in ionic liquids has been reported to successfully catalyze tetrahydropyranylation of alcohols (120). Tetra-hydropyranylation is one of the most widely used processes for the protection of alcohols and phenols in multi-step syntheses. Although the control experiments with the ionic liquids showed negligible activity in the absence of the added acids, high yields of product were obtained with the ionic liquid catalysts TPPTS or TPP.HBr-[BMIM]PF6. By rapid extraction of the product from the acidic ionic liquid phase by diethyl ether, the reaction medium was successfully reused for 22 cycles without an appreciable activity loss. A gradual loss of the catalyst and a reduced volume of the ionic liquid were noted, however, as a consequence of transfer to the extraction solvent. 

TechXtract is an extraction technology that has been used to remove a variety of contaminants from the surfaces of concrete, steel, brick, and other materials. Target contaminant types include organics, heavy metals, radionuclides, and polychlorinated biphenyls (PCBs). The technology uses proprietary chemical formulations in successive steps to remove these contaminants. The process employs as many as 25 different components in 3 separate chemical formulations that are applied to the contaminated surface and then removed in a multi-step, multicycle sequence. TechXtract is commercially available and has been used at multiple sites. 

In search of new natural products, crude extracts are classically subjected to multi-step work-up and isolation procedures which include various separation methods (besides HPLC, for instance, column, gel or counter-current chromatography) in order to obtain pure compounds which are then structurally elucidated by using off-line spectroscopic methods such as nuclear magnetic resonance spectroscopy and mass spectrometry. 

Hibara, A., Kasai, K., and Miyaguchi, H., et al. Novel two-phase flow control concept and multi-step extraction microchip, in "Proceedings of Micro Total Analysis Systems 2008" (L. E. Locascio, M. Gaitan, B. M. Paegel, D. J. Ross, W. N. Vreeland Eds.), pp. 1326-1328. Chemical and Biological Microsystems Society, San Diego, USA, (2008). 

As far as quantitative chemical derivatization GC analysis is concerned, it is necessary to mention especially the work of Gehrke and his collaborators, who specified the fundamental concepts of quantitative GC analysis combined with the chemical derivatization of sample compounds and applied them to the accurate determination of the twenty natural protein amino acids and other non-protein amino acids as their N-TFA-n-butyl esters [5 ], the urinary excretion level of methylated nucleic acid bases as their TMS derivatives [6], TMS nucleosides [7] and other investigations. Further examples include a computer program for processing the quantitative GC data obtained for seventeen triglyceride fatty acids after their transesterification by 2 NKOH in n-butanol [8], a study of the kinetics of the transesterification reactions of dimethyl terephthalate with ethylene glycol [9] and the GC-MS determination of chlorophenols in spent bleach liquors after isolation of the chlorophenols by a multi-step extraction, purification of the final extract by HPLC and derivatization with diazoethane [10]. 

In contrast, if all proteins have to be extracted, e.g. for the study of the grape biology, it is necessary to adopt a multi-step method in order to minimize protein losses occurring with rupture of the cells and proteins interaction with phenolic compounds. 

Basically, different techniques can be employed to optimally concentrate citrus oils distillative, extractive and chromatographic methods are available frequently combined multi-step technologies are used. However, cold procedures are apparently the first choice in citms oil processing (see chapter 2), if the following aspects are considered ... 

Compared to other drugs of abuse, analysis of cannabinoids presents some difficult challenges. THC and 11-OH-THC are highly lipophilic and present in low concentrations in body fluids. Complex specimen matrices, i.e., blood, sweat, and hair, may require multi-step extractions to separate cannabinoids from endogenous lipids and proteins. Care must be taken to avoid low recoveries of cannabinoids due to their high affinity to glass and plastic containers, and to collection devices for alternate matrices (Blanc et al. 1993 Bloom 1982 Christophersen 1986 Joern 1992). THC and THCCOOH are predominantly found in the plasma fraction of blood, where 95% to 99% are bound to lipoproteins. Only about 10% of either... 

When molecules are synthesized by multi-step sequences or when new compounds are extracted from natural sources, their structure and purity must be elucidated. For this, a quantitative elemental analysis must be performed. This particular type of analysis allows us to find the percent elemental composition, in the pure state, of the molecule under study. The measurement of a single element, indeed two (C and H are the most frequent) will verify the accuracy of the molecular formula proposed for a molecule not as yet fully defined but for which a structure has been deduced from spectral studies. Elsewhere, purify of a compound for which the composition and the molecular weight are known, can be determined by comparison of the experimental results obtained from a sample with the theoretical ones (Figure 18.1). 

Furfural and thence furan, by vapour-phase decarbonylation, are available in bulk and represent the starting points for many furan syntheses. The aldehyde is manufactured from xylose, obtained in turn from pentosans, which are polysaccharides extracted from many plants, e.g. com cobs and rice husks. Acid catalyses the overall loss of three mole equivalents of water in very good yield. The precise order of events in the multi-step process is not known for certain, however a reasonable sequence " is shown below. 

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