Soxhlet extraction separation techniques

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,... 

Histamine Extraction. Some secondary plant metabolites are very difficult to extract from their natural matrix and require lengthly soxhlet extractions. Complete histamine extraction was relatively simple. The HPLC separation was used to design a technique to confirm a complete extraction. The histamine peaks from three serial extractions on the same 3 grams of cotton plant leaves are shown in Figure 6. Post-column fluorescence detection of the fourth extraction showed only the slightest response even at the highest detector amplitude. Three extractions accounted for from 95% to 99% of the histamine content. The plant residues from these extractions yielded no additional histamine after standing at ambient conditions for two weeks. 

Classical sample preparation methods such as distillation, soxhlet extraction are still used [839, 840], but specific techniques such as supercritical fluid extraction (SFE) [841], and increasingly in recent years, adsorption techniques such as solid phase micro-extraction (SPME) [841a] are also being used for isolation, separation, and identification of flavor and fragrance materials. 

Polybrominated Diphenyl Ethers. Like PCBs, air samples containing PBDEs are usually collected by pumping air through a sampler containing a glass fiber filter and adsorbent trap to separate the particle bound and vapor phase fractions, respectively (Dobber et al 2000a Hillery et al 1997). The filters and adsorbants are then Soxhlet extracted with acetone/hexane, and the extracts are cleaned-up and analyzed by high resolution GC techniques. 

Microwave-assisted extractions (MAE) can be performed in open (focused MAE) or closed (pressurized MAE) flasks. This technique is commonly used for extractions from complex and difficult sample matrices, replacing time- and solvent-intensive Soxhlet extractions or hydrodistillations.46 MAE is also widely applied to environmental samples, for example, for extracting polycyclic aromatic hydrocarbons (PAH) from soil, methylmercury from sediments, and trace metals and pesticide residues from plant material47 48 The use of microwave treatment instead of hydrodistillation offers a solvent-free separation technique essential oils are heated and dry-distilled 46... 

The coke formed in the 250-450 °C range, has been analysed following the technique proposed by Magnoux et al. [7]. This technique allows for the separation of the external coke from the internal coke by Soxhlet extraction using pyridine. As an example of the results, the fractions of coke extracted directly (external coke), of coke extracted once Si has been dissolved with fluorhydric add (soluble coke) and of the coke that remains insoluble in pyridine are shown in Figure 2, The results correspond to a contact time of 0.05 h and to a time on stream of 30 min. The total coke content as well as each one of their fractions increase with temperature The greater proportion of coke is internally deposited in the zeolite and is soluble in pyridine The external coke content is observed from 300 °C. Above 400 °C there is a coke fraction that is insoluble in pyridine ... 

The chemical extraction procedure used to preferentially disassociate carbonate and silicate minerals is described elsewhere in this Symposium Series (12), and, thus, will be described only briefly here. The separation scheme is outlined in Figure 1. Initially, a bitumen-free oil shale is isolated by exhaustive Soxhlet extraction with a methanol/benzene mixture. A portion of the bitumen-free shale oil is then treated with HC1 to produce a carbonate-, bitumen-free oil shale. Following Soxhlet extraction with benzene/methanol to remove carbonate-associated bitunens, a portion of the carbonate-, bitumen-free oil shale is then extracted with HF/HC1 to produce a silicate-, carbonate-, bitumen-free shale. This shale is also Soxhlet extracted to remove silicate-associated bitumens. Finally, a portion of the silicate-, carbonate-, bitumen-free shale is separated by density into three fractions by sink/float techniques using both 15 wt% ZnCl2 in distilled water and pure distilled water as immersion bath media. 

Solvent Extraction Studies. Techniques necessary to detect lipid species extracted from in vitro and in vivo exposed Biomer were developed. Extractions with a nonpolar swelling solvent (e.g., CHC13) employing a soxhlet apparatus were performed to extract preferentially lipophilic biological components from Biomer or previously isolated neointimal samples. Experimentation demonstrated the high solubility in chloroform of polymer-derived monomeric and oligomeric components. A separation of lipids from these components was therefore required. 

Silicones have been extracted from environmental samples with solvents such as hexane, diethyl ether, methyl isobutylketone, ethyl acetate, and THF, using either sequential or Soxhlet techniques (690-695). Silicones of a wide range of molecular weights and polarities are soluble in THF. This feature, coupled with its volatility and miscibility with water, makes THF an excellent solvent for the extraction of silicones from wet samples, ie, soils and sediments. Trace levels of silicones extracted from environmental samples have been measured by a number of techniques, including atomic absorption spectroscopy (AA), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), pyrolysis GC-MS, as well as H and Si NMR spectroscopy (674,684,692,696-700). The use of separation techniques, such as gel permeation and high pressure liquid chromatography interfaced with sensitive, silicon-specific AA or ICP detectors, has been particularly advantageous for the analysis of silicones in environmental extracts (685,701-704). 

Soxhlet extraction is chiefly applied to the separation of relatively nonvolatile analytes from solid samples. For example, this technique is useful for extracting pesticides, PCBs, and PCDD/ F CDFs from various matrices, including fatty tissue. soil, and paper [177],[178], The advantage of the method is high yield, achieved by continuous extraction of the sample with fresh extractant. Disadvantages include the considerable amount of time required (typically several hours to several days), the thermal stress to which analytes are subjected, and the fact that the analytes are obtained in very dilute form in a solvent, and must therefore be concentrated in a subsequent step. Any fat present in the sample is co-extracted. and this must also be removed separately. 

---