Boiling solvent methods, extraction

The classical methods of solvent extraction of polymers can be conveniently divided into those for which heat is required (Soxhlet/Soxtec ), and those methods for which no heat is added, but which utilise some form of agitation, i.e. shaking or sonication (Table 3.3). Other LSE procedures consist in soaking the polymer in boiling solvents [84,85] and cold LSE [80,86]. These methods are also time-consuming, use large amounts of solvents which are scheduled to be restricted in the future, and exhibit other limitations when analytes are present in small quantities, where they may actually be lost in concentration steps following extraction. Many norms are still based on such standard procedures [87,88],... 

For the extraction of rubber and rubber compounds a wide variety of solvents (ethyl acetate, acetone, toluene, chloroform, carbon tetrachloride, hexane) have been used [149]. Soxtec extraction has also been used for HDPE/(Tinuvin 770, Chimassorb 944) [114] and has been compared to ultrasonic extraction, room temperature diffusion, dissolution/precipitation and reflux extraction. The relatively poor performance of the Soxtec extraction (50% after 4h in DCM) as compared with the reflux extraction (95% after 2-4 h in toluene at 60 °C) was described to the large difference in temperature between the boiling solvents. Soxtec was also used to extract oil finish from synthetic polymer yam (calibration set range of 0.18-0.33 %, standard error 0.015 %) as reference data for NIRS method development [150]. 

This cycle of vaporisation of the solvent, condensation, extraction, and vacuum-filtration may be repeated any number of times in a solid-fluid serial extractor. The occurrence of an extractive material fluid bed as a result of the flow of boiling hot vapour provides for effective extraction, while pressure filtration provides for short cycle times. This functional principle makes it possible to achieve filtration pressures which are 50-100 times more effective than when using the Soxhlet method, where only the low hydrostatic pressure of the extractive fluid operates. Solid-fluid-vortex extraction according to the proprietary FEXTRA (Feststoff Extraktion) principle is low cost. 

The study of the properties and applications of clusters requires them to be accessible on a preparative scale and this is often conditioned by the ease with which they can be separated from other reaction products. Because their molecular weights are not too high, several tetranuclear clusters are volatile and/or soluble in organic solvents, and therefore the first methods of separation to be considered are sublimation under high vacuum (if the compound is thermally stable) and crystallization. When the solubility is low, continuous extraction with low boiling solvents can be tried50. ... 

Solid samples are extracted with low-boiling solvents. As the polarity of the volatiles is different, a two-step extraction procedure is recommended, e.g. methylene chloride as the first solvent and diethyl ether as the second solvent [13]. The yield of the odorants is enhanced when the dry sample is soaked in water before the extraction procedure [14]. After filtration and drying, the extract is concentrated to approximately 50 mb and is then freed from the non-volatile material by using the solvent-assisted flavour evaporation (SAFE) method (Sect. 16.2.2.2). 

The distillation method of moisture determination requires collection and determination of the water evolved from the coal when the sample is heated in a boiling solvent that is itself immiscible with water. The solution and extraction methods require either solvent extraction of the water from the coal (followed by subsequent determination of the water content of the solvent) or use of a standard reagent that will exhibit differences in concentration by virtue of the water in the coal. A nonthermal solvent method of determining moisture involves the use of an extraction procedure in which the coal is shaken with a solvent that extracts the water from the coal. The degree of change in some physical property of the solvent, such as density, is then used as a measure of the water extracted. 

Separation is carried out using various techniques, depending on the nature of the compounds. For nonionic species the solubilities of the compounds are generally low and similar, and it has been necessary to use either fractionation by continuous extraction with low boiling solvents (36) or thin-layer chromatography (58, 60). The first method has been used with air-sensitive compounds, whereas the second has been applied only to air-stable substances. In both cases, it is possible to separate only limited amounts of compounds, whose characterization is, therefore, carried out using particular techniques such as mass spectroscopy (58-60). 

A second approach is to homogenize the sample in some traditional fashion (blender or mortar and pestle) followed by Soxhlet extraction with an appropriate solvent. In this procedure, the solvent is boiled and clean solvent re-extracts the food product each time. This method is effective however, it is quite slow often taking 24 h per sample in order to obtain good recoveries. The analyte must boil at a higher temperature than the solvent for good recovery. Recently, there have been innovations in solvent extraction that combine hot solvent leaching and traditional Soxhlet extraction (Majors, 1996). The sample is first immersed in boiling solvent and then the thimble is raised for... 

In general, method development in MAE involves optimization of solvent composition, solvent volume, extraction temperature and extraction time. The temperature of the solvent/sample mixture is usually well above the boiling point of the solvents). Hence, MAE utilizes in a similar manner as in PLE the enhanced solvent strength and faster diffiisivity of a heated solvent. For more discussions on optimization of MAE and various applications, please consider chapter 9 of this book as well as several review articles (6,7,49,50,63). 

We have derived an extraction method that retains the convenience of the ball-mill tumbler for large numbers of extractions, and have investigated various solvent systems for improved recoveries. Preliminary results indicate that a tumbler extraction using methanol and dichloro-methane recovered hydrocarbons from an intertidal sediment as efficiently as the soxhlet technique (12). This report describes improvements in our tumbler procedure and compares it with three boiling-solvent procedures (10,13,15). 

Ball-Mill Tumbler Extraction. To avoid unnecessary cost, inconvenience, and hazards involved in extracting large numbers of sediment samples with boiling solvents (6), we have investigated alternative procedures. Ideally, a suitable procedure should extract efficiently and reproducibly and be simple, safe, and convenient. In particular, we needed a method that used minimal benchtop or hood space could... 

The SFE technique was compared to the boiling liquid methods performed with the following solvents 1) acetone, 2) ethanol, 3) methanol, 4) water, and 5) water/methanol (70 30 vfv). The SFE method showed the highest extraction efficiency and reproducibility (RSD<5%, n = 3) for removing terpene trilactones from the ginkgo leaves in comparison with the solvent extraction methods. The total efficiencies for recovety of bilobalide and gingkolides (A, B, and C) with the solvent based methods were 60 91% relative to the SFE results (Table I). 

Another method for the extraction of aromatics is the DMSO process developed by the Institut Francais du Petrole (/FP), which uses dimethyl sulfoxide (DMSO) as a solvent with the addition of around 10% water, in two extractors (Figure 4.10). The extraction of aromatics takes place in the first extractor, while the second extractor is used to recover the solvent by extraction with a low-boiling, paraffinic auxiliary solvent, such as butane. 

---