Soxhlet extraction techniques

The classical Soxhlet extraction technique has seen some improvements, mainly in the submersion of the whole extraction thimble into the boiling extraction solvent, degree of automation, and in reduction of solvent volume. In a recently introduced universal extraction system (Biichi) four SLE methods are contained in one device Soxhlet Standard, Soxhlet warm, hot extraction and continuous flow. It is possible to use solvents with boiling points of up to 150 °C inert gas can be supplied during the extraction process. 

Although the Soxhlet extraction technique is termed a classical method , it is still applied regularly for the extraction of non-ionic surfactants from solid matrices. The advantages of this technique are its robustness (virtually any solid matrix can be extracted) and the fact that no expensive equipment is needed. 

The infrared method that has been used most frequently (EPA 418.1) is appropriate only for water samples. A separatory funnel liquid-liquid extraction technique is used to extiact hydrocarbons from the water. A method (EPA 5520D) using a Soxhlet extraction technique is suitable for sludge. This extiaction is frequently used to adapt the method (EPA 418.1) to soil samples. An infrared-based supercritical fluid extraction method for diesel range contamination (EPA 3560) is available. 

Excision reactions tend to be low yielding, and can often benefit from the use of Soxhlet extraction techniques. Only a very few excision reactions have beenreported to succeed in dismantling a 3D cluster-containing framework (143-145). 

A sohd phase extraction-HPLC method, employing a Soxhlet extraction technique to recover LAS from soil matrices, is described for these determinations which gave an average recovery of LAS (2-15 ug g spikes) of 97%. 

Substances that are very sparingly soluble in ether are best reduced by the so-called Soxhlet extraction technique. The following directions are recorded for the preparation of tryptamine 95... 

Dissolution of the powder. After homogenising the powder, obtained either directly by drilling or by cmshing core shces, a part is weighed precisely and dissolved in a constant amount of liquid, most frequently in concentrated nitric acid solution with ISA (ionic strength adjuster). In this way the total or acid soluble chloride content is determined. The dissolution process is the most important step determining the reproducibility of the chloride analysis. Alternatively, the Soxhlet extraction technique (reflux of boiling water on the concrete powder for 24 h) is used to dissolve chloride ions. Both methods result in a similar total chloride content. 

A soil/sediment or contaminated sludge with a very high solids content can be extracted via Soxhlet extraction techniques or more conveniently via ultrasonic probe sonication into a mixture of TCTFE and a carefully weighed amount of soil/sediment/sludge. 

Unfortunately the water soluble techniques produce results that are difficult to reproduce so they are rarely used in the United Kingdom or Europe, although the soxhlet extraction technique , a method of refluxing concrete chips in boiling water to extract the chloride is a standard technique used in North America. See, for example, AASHTO T260 Sampling and Testing for Total Chloride Ion in Concrete and Concrete Raw Materials which includes a procedure for water soluble ion sample preparation and analysis. 

The amount of chloride ion in the concrete can be measured by sampling the concrete and carrying out chemical analysis (titration) on a liquid extracted from the sample. This is usually done by mixing acid with drillings or crushed core samples. An alternative is pore extraction by squeezing samples of concrete or, more usually mortar. This technique is frequently used in laboratory experimental work as it is often difficult to extract useful pore water samples from field concrete. The soxhlet extraction techniques for free chlorides was discussed earlier. 

The gel content of the samples was determined using a Soxhlet extraction technique. The samples were first extracted with boiling water (12 h) to remove the TPS phase and then they were extracted with hot xylene for 4 h and 8 h. The samples were placed in folded 120 mesh stainless steel cloth cages. The samples and cages were weighed before extraction. The extracted samples were then dried at 80 °C until there was no further weight loss. The gel content was calculated from the following equation ... 

This is a relatively new technique that is used for PCBs and other nonpolar, volatile and semi-volatile organic compounds. Typically, a small aliquot of soil sample (0.5-20 g) is used for the extraction. Soil samples are extracted with one or more organic solvents using microwave energy at elevated temperature (100-115 °C) and pressure (50-175 psi). This method uses less solvent and takes significantly less time than Soxhlet extraction but is limited to thermally stable compounds. 

Standardisation of EPDM characterisation tests (molecular composition, stabiliser and oil content) for QC and specification purposes was reported [64,65]. Infrared spectroscopy (rather than HPLC or photometry) is recommended for the determination of the stabiliser content (hindered phenol type) of EP(D)M [65]. Determination of the oil content of oil-extended EPDM is best carried out by Soxhlet extraction using MEK as a solvent [66], A round robin test was reported that evaluated the various techniques currently used in the investigation of unknown rubber compounds (passenger tyre tread stock formulations) [67]. 

To obtain representative samples from nonhomoge-neous sample materials, such as polymer compounds, particle-size reduction techniques need often to be applied (not for film) [50]. Also, for destructive inpolymer additive analysis it is advantageous to change the physical state of solid samples to provide a larger surface area per unit mass. Complete extraction is sometimes achieved only after grinding the sample. Typically, Perlstein [51] has reported recoveries of only 59 % for extraction of Tinuvin 320 from unground PVC after 16 h of Soxhlet extraction with diethyl ether while recoveries rise to 97 % for ground polymer. 

Extraction techniques for polymeric matrices can be divided into traditional and new . The traditional techniques include Soxhlet extraction, boiling under reflux, shaking extraction and sonication. All these methods are at atmospheric pressure. When the sample is added to a solvent, which is boiled under reflux (i.e. at the highest possible temperature without applying an external pressure) extractions tend to be much faster than Soxhlet extractions. Examples are the Soxtec ,... 

Applications The determination and quantification of oligomers from PET has been carried out using various techniques Soxhlet extraction followed by gravimetric analysis with identification by HPLC-DAD, selective precipitation of the polymer (from a trifluoroacetic acid solution), and chloroform extraction under pressure in a sealed Parr bomb [112]. Heating of a 1 g sample in 20 mL chloroform at 100 °C for 2h allows a precision of 5 %. 

It is not uncommon that extraction techniques are unfairly compared. Appropriate interlaboratory studies are few. Soxhlet and sonication extraction (EPA methods 3540 and 3550, respectively) were compared in an interlaboratory study (129 participants) for PCBs in soil. Results from laboratories using Soxhlet extraction were significantly more accurate than those obtained using sonication, especially at higher concentrations, but with equal precision [196]. This is rationalised by the observation that the Soxhlet procedure presents the sample with fresh solvent so that the extraction solvent is never saturated, unlike the sonication procedure. Sonication is very sensitive to the solvent polarity, nonpolar solvents producing considerably less accurate results than polar solvents. It is not as sensitive to clean-up procedures as... 

Desrosiers [23] has dared ranking extracting methods as follows (in order of preference) SFE, US, hot block or MAE, Soxhlet (to be phased out as quickly as possible). Munteanu [556] has evaluated extraction techniques for additives from polymers prior to chromatographic analysis (up to 1990). The analytical extraction of additives from polymers has recently critically been reviewed with emphasis on SFE, MAE and ASE [92]. Dean [272] compared modem extraction techniques, with focus on environmental analysis. 

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