Accelerated solvent extraction soil samples

Zuloaga O, Etxebarria N, Fernandez LA, Madariaga J. Comparison of accelerated solvent extraction with microwave-assisted extraction and Soxhlet for the extraction of chlorinated biphenyls in soil samples. Trends Anal. Chem. 1998 17 642-647. 

Another method (EPA 3545, accelerated solvent extraction) has been validated using a variety of soil matrixes, ranging from sand to clay. In the method, conventional solvents such as methylene chloride (or a hexane-acetone mixture) are heated [100°C, (212°E)] and pressurized (2000 psi), then passed through the soil sample (this technique is also suitable for application to petroleum sludge and petroleum sediment). The method has the advantage of requiring smaller solvent volumes than is required by traditional solvent extraction techniques. 

The extraction of pesticides from soil samples using accelerated solvent extraction is a good example of an analytical procedure fulfilling the rules of green chemistry. This procedure has many advantages over the classical techniques used for extracting analytes from complex matrices. 

A method for determining CDDs in municipal incinerator fly ash has been reported (Alexandrou and Pawliszyn 1990). The method uses supercritical fluid extraction (SFE) to recover CDDs from fly ash samples prior to GC. Supercritical fluid extraction is faster and less expensive than the typically used Soxhlet extraction and gives quantitative removal of CDDs and CDFs from fly ash. Extracts obtained using SFE will still require additional clean-up steps prior to analysis. Supercritical C02 has also been used to assist solvent-based extraction of CDDs from soils (Friedrich and Kleibohmer 1997). In this case, the supercritical fluid was combined with accelerated solvent extraction (liquid extractions conducted under elevated temperature and pressure) to provide good recoveries relative to Soxhlet extractions. 

For example, in the analysis of chlorophenol in soil by accelerated solvent extraction followed by GC-MS, deuterated benzene may be used as the matrix spike. The deuterated compound will not be present in the original sample and can easily be identified by GC-MS. At the same time, it has chemical and physical properties that closely match those of the analyte of interest. 

Soil, sediment, and dust samples were prepared in a similar way before analysis. After the pre-cleanup steps and homogenization, FRs were extracted from samples using different solid-liquid extraction techniques. The most commonly used technique was accelerated solvent extraction (ASE), which enables the fast extraction of samples using different solvents such as hexane and dichloromethane [98-100]. Other commonly used techniques for these samples were ultrawave-assisted extraction (UAE) [97], which also enabled quick extraction, and the more time-consuming but very efficient technique, Soxhlet extraction [96]. Some authors have also described less common techniques such as microSPE [95]. There is also information that many FRs that are no longer produced (mainly PCBs and PBDEs) are present in dusts, soils, and sediments in very high amounts, even 390 pg/g [98]. 

Hubert, A., Wenzel, K.-D., Manz, M., Weissflog, L., Engewald, W., and Schuiirmann, G., High extraction efficiency for POPs in real contaminated soil samples using accelerated solvent extraction. Anal. Chem., 72, 1294-1300, 2000. 

Guzella, L. and Pozzoni, F., Accelerated solvent extraction of herbicides in agricultural soil samples, Int. J. Environ. Anal. Chem., 74, 123-133, 1999. 

In situ generated micelles have been applied to the inspection of aniline pesticidic metabolites in lake water. The separation of 16 PAH in SUA oligomer electrolytes was reported. Creosote-contaminated soil samples were extracted by accelerated solvent extraction using methylene chloride-acetone mixtures. The extracts were further fractioned by gel permeation chromatography before analysis. The EKC chromatogram of a creosote-contaminated soil fraction shows the resolution of at least 50 peaks. The separation of the 11 priority phenols in river and sea water was demonstrated in MEKC with DBTD surfactants, whereas examples of the use of liposomes as carriers include the separation of benzene derivatives and phenols." ... 

Yes, there have been comparative studies in which the percent recovery has been measured using not only SFE but also ASE and comparing these results to percent recoveries from the more conventional Soxhlet extraction (S-LSE). Generally, these studies are done on certified reference samples or on grossly contaminated samples. We will discuss two studies from the recent analytical chemistry literature. The first study compared the efficiencies of SFE, high-pressure solvent extraction (HPSE), to S-LSE for removal of nonpesticidal organophosphates from soil (46). HPSE is very similar to accelerated solvent extraction however, we will reserve the acronym ASE for use with the commercial instrument developed by Dionex Corporation. HPSE as developed by these authors used parts available in their laboratory.. The authors compared S-LSE with SFE and HPSE for extraction of tricresyl phosphate (TCP) and triphenyl phosphate (TPP) from soil. Molecular structures for these two substances are as follows ... 

Pressurized liquid extraction (PLE) is also known as pressurized solvent extraction (PSE), enhanced solvent extraction (ESE), pressurized fluid extraction (PEE), or accelerated solvent extraction (ASE ) in the literature. PLE is considered an environmentally friendly extraction technique because it requires only small volumes of solvents. PLE was primarily used for the extraction of environmental samples, such as soils and sediments. Elevated temperatures (usually between 50 and 200 °C) and pressures (between 10 and 15 MPa) are used in closed vessels, which allow extractions to be completed in a very short time. High pressure allows the solvent to remain in its liquid state even at temperatures above its boiling point, and forces it into the matrix pores. High temperatures decrease the solvent viscosity and increase metabolite solubilization, the diffusion rate, and mass transfer kinetics, thus facilitating desorption of the analytes from the plant material. Most PLE applications reported in the literature employ the same organic solvents as those commonly used in conventional solid-liquid extraction techniques. When water is used as the extraction solvent, the technique is referred to as pressurized hot water extraction (PHWE). Extractions are carried out in stainless steel extraction cells of various volumes (typically 1-250 mL). One extraction cycle is generally applied for 5-20 min at temperatures ranging from 50 to 140 °C in the vast majority of applications. 

The mode of extraction for PAHs is highly dependent on the matrix. For solid-based matrices such as food samples, sediments, soil, marine organisms, etc. extraction methods such as Soxhlet extraction with nonpolar solvent [35 6], hollow fiber membrane solvent microextraction (HFMSME) [10], pressimzed hquid extraction (PLE) [37,38], sonication extraction [3], microwave-assisted extraction (MAE) [3], supercritical fluid extraction, (SEE) [39], accelerated solvent extraction (ASE) [40], cold extraction [41], soxtec extraction [42], microwave-assisted alkaline saponification (MAAS) [43], dynamic microwave-assisted extraction (DMAE) [44], add-induced cloud point extraction (ACPE) [45], methanolic saponification extraction (MSE) [7], etc. are employed. Of all these, Soxhlet extraction is the most common for solid samples and has achieved excellent extraction with high-level recovery but its setback is the high consmnption of solvent and time associated with it. 

Engewald, W, and Schiiiirmann, G. (2001) Accelerated solvent extraction- more efficient extraktion of POPs and PAHs fi-om real contaminated plant and soil samples. Rev. Anal. Chem., 20, 101-144. 

A recent study published in the Chinese Journal of Instrumental Analysis, Fenxi Ceshi Xuebao, showed a detection limit of 500 ng of Sulfur Mustard (HD) by using accelerated solvent extraction-gas chromatography (ASE-GC) coupled with a flame photometric detector (EPD) in the sulfur mode, in soil. In this case, the study showed evidence that ASE results in better recoveries and sensitivity than liquid solid extraction (LSE) [50]. In 1996, a paper was published on a method for the analysis of Lewisite through derivatization of the compound before introduction into a gas chromatograph. In order to simplify the derivatization process, a tube packed with absorbent was used for collection of airborne vapors. If a positive response occurs when screening analytes using a GC coupled with an FPD, then the same sample can be analysed using a GC equipped with an AED for confirmation based on the elemental response to arsenic (in the case of Lewisite) and sulfur (in the case of Sulfur Mustard) within the appropriate GC retention time window [54]. 

Soxhlet, sonication, supercritical fluid, subcritical or accelerated solvent, and purge-and-trap extraction have been introduced into a variety of methods for the extraction of contaminated soil. Headspace is recommended as a screening method. Shaking/vortexing is adequate for the extraction of petroleum hydrocarbons in most environmental samples. For these extraction methods, the ability to extract petroleum hydrocarbons from soil and water samples depends on the solvent and the sample matrix. Surrogates (compounds of known identity and quantity) are frequently added to monitor extraction efficiency. Environmental laboratories also generally perform matrix spikes (addition of target analytes) to determine if the soil or water matrix retains analytes. 

Begin this method with the Soxhlet extraction of approximately 1 to 10 g of soil or sediment with 90% methanol/10% distilled water. The methanol will effectively wet the soil and sediments and remove the majority of the organochlorine pesticides. Alternatively, the soils and sediments may be extracted with heated solvent under pressure using the accelerated solvent extractor by Dionex (see Chapter 9 on the extraction of food and natural materials for details of analysis). After the extraction is complete, dilute the methanol extract with distilled water to a final concentration of 10% methanol. Process the extract through a C-18 cartridge as described in Section 7.10.1. In this case, the C-18 sorbent with greater hydrophobicity is used because of the 10% methanol present in the sample. Elute the cartridge with ethyl acetate and analyze by GC/MS. 

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