Soxhlet extraction characteristics

Principles and Characteristics In boiling under reflux procedures a small amount of ground polymer (typically 3g) is placed in a headspace jar (typically 100 mL) and solvent (typically 30 mL) is added. After sealing, the jar is placed in an oven at a temperature where the solvent slowly refluxes. The solvent is, therefore, at the highest temperature possible without applying an external pressure. Consequently, reflux extractions tend to be much faster than Soxhlet extractions. Examples are Soxtec , Soxtherm , FEXTRA and intermittent extraction. Whilst, in theory, partitioning of the analyte between the polymer and solvent prevents complete extraction, this hardly ever constitutes a problem in practice. As the quantity of solvent is much larger than that of the polymer, and the partition coefficients usually favour the solvent, very low additive levels in the polymer result at equilibrium. Any solvent or solvent mixture can be used. 

Table 3.8 Main characteristics of conventional Soxhlet extraction...

On-line SFE-SFC modes present several distinct advantages that are beyond reach of either technique when used separately (Table 7.13). An obvious advantage of SFE is that it is an ideal way to introduce a sample into an SFC system. Because the injection-solvent is the same as the mobile phase, in this respect the criteria for a successful coupling of different techniques are fulfilled [94], i.e. the output characteristics from the first instrument and the input characteristics of the second instrument are compatible. Supercritical fluid techniques can separate high-MW compounds are significantly faster than classical Soxhlet extractions and require less heat and solvent. SFE-SFC techniques are versatile,... 

The catalyst was removed and analyzed for its coke content, pore size distribution, pore volume, and surface area. All the catalyst samples were analyzed after a Soxhlet extraction with tetrahydrofuran for 24 h and drying in oven at 100 C. The catalyst weight loss due to combustion at 550 C was considered as the coke on catalyst. The catalyst pore characteristics were measured by a Quantachrome Autoscan Porosimeter. 

The Soxhlet extraction method discussed in Section 6.6 can be used to separate the sol and gel fractions of a gel in the gelation regime, allowing direct determination of the gel fraction gel- Percolation theory expects the molar mass of a network strand M to be the same as the characteristic molar mass in the sol fraction. Hence, M can be determined by the size exclusion chromatography methods of Section 6.6, applied to the sol fraction. Equation (7.93) is tested in Fig. 7.19, where the shear modulus is shown to be proportional to Pgei/M. ... 

Figure 1. Scanning electron micrographs of untreated (A), Soxhlet-extracted (B), and MAP-treated (C) fresh peppermint leaves (Mentha piperita L. Mitchum). The Soxhlet was carried out for 6 hours whereas the MAP treatment consisted of a single irradiation of 20 seconds. Hexane was used as solvent in both cases. Note the loss of structural characteristics of the surface of the Soxhlet-extracted specimen. The secretory gland is much reduced in size with the appearance of a deflated balloon as a result of the permeation and diffusion processes through its walls. Cavities created by the localised explosion of secretory glands characterise the MAP-treated sample (figure adapted from reference [6]).

The FTIR spectra of original alkyd resin and soxhlet extracted resin are shown in Figure 2 which shows the characteristic peaks of ester stretching (COOR) at 1729.49 cm, unsaturated fatty acid at 1266.23 cm and aromatic CH deformation at 730cm closely matches thus establishing that alkyd resin has been successfully encapsulated within urea-formaldehyde shell. 

B, products giving positive Tollen s Reagent tests were obtained. No attempts were made to isolate either 9A or 9B since previous work had indicated that such compounds were subject to decomposition, and bromine oxidation was attempted on the crude reaction mixture. For both systems, as bromine addition was carried out, a transient blue color was noticed and white precipitates appeared in the reaction mixtures. In order to obtain 11A and IIB in purer form, the precipitated crude polymer was subjected to Soxhlet extraction with ethanol. This was followed by azeotropic distillation of benzene over the insoluble products. These two purification steps removed most of the non-polymeric by-products including unreacted or partially reacted nitro compounds as well as water and ethanol. Both llA and IIB showed strong IR absorption at 1200 cm" characteristic of the trans nitroso dimer bond, and a medium sharp absorption... 

For several polymers obtained by these methods the N,N -diisopropylurea side-product was not completely removed by the reprecipitation sequence. The urea crystals were clearly present as an entrapped separate phase under the microscope and displayed a characteristic transition on the DSC. These pol3nners were purified by Soxhlet extraction with methanol for three days. 

Principles and Characteristics The principle of solid-fluid-vortex extraction, a recent development [152], is based on the creation of a relatively high filtration pressure as a result of cooling off a vapour chamber in a boiler vessel in such a way that there is (ideally) complete condensation and the extractive fluid is forced through a filter and/or extraction material at nearly one atmosphere in the case of open extractor systems and at more than one atmosphere in the case of closed extractor systems (cf. hydrostatic pressures up to 0.01 bar in Soxhlet). 

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