Ultrasonic extraction

Soxhlet can be applied universally to almost any sample. It is not uncommon to use Soxhlet as the benchmark method for validating other extraction techniques. Soxtec reduces the extraction time to 2 to 3 hours as compared to 6 to 48 hours in Soxhlet. It also decreases solvent use from 250 to 500 mL per extraction to 40 to 50 mL per extraction. Two to six samples can be extracted simultaneously with a single Soxtec apparatus. 

Foster and Gonzales [10] reported a collaborative study by 11 laboratories of Soxtec and Soxhlet methods for the determination of total fat in meat and meat products. Each lab analyzed six samples canned ham, ground beef, frankfurters, fresh pork sausage, hard salami, and beef patties with added soy. In general, results for the Soxtec system showed improved performance. The method was first adopted by AOAC International for the extraction of fat from meat. Membrado et al. [11] tested Soxtec against Soxhlet extraction for the extraction of coal and coal-derived products. Optimization of Soxtec operating conditions reduced the total extraction time to 10% of what was needed by Soxhlet extraction. The recovery and precision by the two methods were comparable. 

Ultrasonic extraction, also known as sonication, uses ultrasonic vibration to ensure intimate contact between the sample and the solvent. Sonication is relatively fast, but the extraction efficiency is not as high as some of the other techniques. Also, it has been reported that ultrasonic irradiation may lead to the decomposition of some organophosphorus compounds [12]. 

the selected solvent system and the operating conditions must demonstrate adequate performance for the target analytes in reference samples before it is implemented for real samples. This is particularly important for low-concentration [parts per billion (ppb) level] samples. 

Like Soxhlet, sonication is also recognized as an established conventional method, although it is not as widely used. Limited research has focused on sonication per se or its comparison with Soxhlet. Qu et al. [13] developed a method using sonication with methanol for the extraction of linear alkylbenzene sulfonate (LAS) in plant tissues (rice stems and leaves). Both efficiency and accuracy were found to be high. The mean recovery was 89% (84 to 93% for LAS concentration of 1 to 100 mg/kg), and the relative standard deviation (RSD) was 3% for six replicate analyses. Its advantages over Soxhlet extraction were speed (1 hour), less solvent consumption, and smaller sample requirement (2 to 3 g). 

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Extraction efficiencies with shaking and ultrasonic extraction were lower than those with solvent reflux extraction. 

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]. 

On a laboratory scale, generally an ultrasonic probe (horn) and an ultrasonic cleaner are used. The ultrasonic field in an ultrasonic cleaner is not homogeneous. Sonication extraction uses ultrasonic frequencies to disrupt or detach the target analyte from the matrix. Horn type sonic probes operate at pulsed powers of 400-600 W in the sample solvent container. Ultrasonic extraction works by agitating the solution and producing cavitation in the... 

Applications Extraction is typically accomplished by refluxing the polymer in an appropriate solvent for l-48h [84,199]. In many cases, ultrasonic exposure reduces the extraction time [90,200], According to Table 3.5 there are several reports of US extraction from polymers. Ultrasonic extraction has been used for HDPE/(BHT, Irganox antioxidants, Isonox, Cyasorb, Am 340, MD 1024, Irgafos 168) [56], LDPE/Chimassorb 81 [201], SBR/tri(nonylphenyl) phosphite [200], HDPE/(Tinuvin 770, Chimassorb 944) [114], etc. Nielson [90] compared the recoveries obtained for a variety of analytes from PP, LDPE and HDPE with Soxhlet, ultrasonic bath and microwave oven. For all samples, the ultrasonic extraction could be achieved within 1 h. For LDPE and PP most compounds (except Irganox 1010) were extracted within 10 min. Further experiments by Nielson [56] on extraction from HDPE confirmed these results. Where phosphite antioxidants (such as Irgafos 168) are present the use of the solvent mixture DCM-cyclohexane was preferred as it prevented hydrolysis of the phosphite by extraction solvents such as alcohols [56]. Similarly, phosphite esters also undergo hydrolysis... 

Brandt [200] has extracted tri(nonylphenyl) phosphite (TNPP) from a styrene-butadiene polymer using iso-octane. Brown [211] has reported US extraction of acrylic acid monomer from polyacrylates. Ultrasonication was also shown to be a fast and efficient extraction method for organophosphate ester flame retardants and plasticisers [212]. Greenpeace [213] has recently reported the concentration of phthalate esters in 72 toys (mostly made in China) using shaking and sonication extraction methods. Extraction and analytical procedures were carefully quality controlled. QC procedures and acceptance criteria were based on USEPA method 606 for the analysis of phthalates in water samples [214]. Extraction efficiency was tested by spiking blank matrix and by standard addition to phthalate-containing samples. For removal of fatty acids from the surface of EVA pellets a lmin ultrasonic bath treatment in isopropanol is sufficient [215]. It has been noticed that the experimental ultrasonic extraction conditions are often ill defined and do not allow independent verification. 

U.S. Environmental Protection Agency (EPA), Method 3550, Ultrasonic Extraction (January 1995). 

Recovery procedures have traditionally involved some form of solvent, gas or heat extraction from the bulk sample matrix. Some of these lend themselves to precolumn hyphenation (e.g. SFE, TD, Py, HS), as opposed to others (e.g. Soxhlet, ultrasonics). Extraction of additives should not be considered as an isolated step, because it may strongly influence the subsequent chromatographic separation. The success of an analysis may very often depend more on the extraction procedure than on the chromatographic separation. In hyphenation there should be compatibility between the sample preparation and subsequent chromatographic analysis. 

PLE pressurized liquid extraction, SPE solid phase extraction, UE ultrasonic extraction, DSPE dispersive solid phase extraction, SBSE stir bar sorptive extraction, TD-GC-MS thermal desorption-gas chromatography-mass spectrometry, LAS linear alkylbenzene sulfonates, CDEAs coconut diethanol amides, NPEOs nonylphenol ethoxylates, DP degradation products, SPC sulphenyl carboxylates, PCDD dibenzo-p-dioxins (PCDD), PCDF dibenzofurans, PCBs biphenyls... 

In recent years, extraction methods for PhACs have usually been based on liquid partitioning with ultrasonic extraction (USE) [43-47], microwave-assisted extraction (MAE) [48], or the more advanced PLE [49-52]. When compared to the other extraction techniques, PLE provides good recoveries, saves time and organic solvent, which makes it become currently a preferred technique for PhAC analyses. 

Ultrasonic extraction is a well-known commercial method to increase mass transfer rate by cavitation forces. Bubbles in the liquid-solid extraction using UE can explosively collapse and produce localized pressure, improving the interaction between the intracellular substances and the solvent to facilitate the extraction of the phytochemical. 

Natural river sediment E2, EE, El Ultrasonic extraction with GC-MS/MS DCM, HPLC fractioning, derivatization 0.04-5 [42]... 

NOR, LEV, PROG Ultrasonic extraction with MeOH-acetone, SPE (C18) HPLC-MS (PI-ESI) (SIM) 0.04 [46]... 

Soil extraction using all types of aqueous solutions and ultrasonic agitation has been carried out. Simple apparatus such as extractant and aqueous solvent in an Erlenmeyer flask or test tube are used. An ultrasonic bath with Erlen-meyer flask is shown in Figure 11.7 (the use of an ultrasonic horn is shown in Figure 12.9). Ultrasonic extraction is typically carried out when the soil particles are not well separated, such as high clay soils, and thus the surfaces are not exposed to the extracting solutions. 

Tan [71] devised a rapid simple sample preparation technique for analysing polyaromatic hydrocarbons in sediments. Polyaromatic hydrocarbons are removed from the sediment by ultrasonic extraction and isolated by solvent partition and silica gel column chromatography. The sulphur removal step is combined into the ultrasonic extraction procedure. Identification of polyaromatic hydrocarbon is carried by gas chromatography alone and in conjunction with mass spectrometry. Quantitative determination is achieved by addition of known amounts of standard compounds using flame ionization and multiple ion detectors. 

Onuska and Terry [14] have described a method for the determination of chlorinated benzenes in bottom sediment deposits. Sample preparation methods using Soxhlet extraction, ultrasonic extraction or steam distillation were compared. The chlorinated benzenes were characterized by open tubular column gas chromatography with electron capture detection. In recovery studies using sediments with different organic matter contents, the steam distillation method was the most efficient. Detection limits were in the range 0.4-10pg kgy1. 

Novikova [21] has reviewed the literature (209 references) covering the extraction, clean-up and analysis of organochlorine (and organophosphorus) insecticides in soil. Johnson and Starr [22] and Chiba and Morley [4] have studied factors affecting the extraction of Dieldrin and Aldrin from different soil types ultrasonic extraction was recommended by these workers. Lopez-Avila et al. [23] used microwave assisted extraction to extract chlorinated insecticides from soils. 

Ou et al. [42] used methanol-ultrasonic extraction followed by clean-up with aluminium oxide, and enrichment with a C-18 SPE column for the determination of LAS in plant tissues by HPLC. Both efficiency and accuracy of the overall method were high, with a mean recovery of 89% (84-93% for LAS concentrations ranging from 1 to 100 mg kg-1) and a repeatability of 3% relative standard deviation for six replicate analyses. With a 2 g sample for analysis, LAS levels of 0.5 mg kg-1 in plants could be detected with the proposed method. 

Previous investigations of heterogeneous sonochemistry have involved ultrasonic extraction of pollutants from sediments and ultrasound assisted reactions employing solid catalysts. However, more extensive quantitative results are needed concerning sonochemistry in environmentally relevant systems. We report results of a preliminary set of experiments, involving the ultrasonic irradiation of bromobenzene, trichloroacetonitrile, and chloropicrin in the presence of silica solids (15 im and 10 nm). 

Ideally, the pollutants to be determined should be removed from the matrix as completely as possible with a minimum amount of the other non-target components. This type of selectivity was certainly anticipated from supercritical fluid extraction. However, trace organic pollutants cover a wide range of polarity, volatility, and molecular size, making selective extraction very difficult to achieve. Currently the most popular extraction methods are Soxhlet [191,400, 402-404], blending [189, 408, 409, 411-455], liquid column extraction and ultrasonic extraction [456], and more recently supercritical fluid extraction [386,456-463]. 

Soil, sediment Sample mixed with anhydrous powdered Na2S04, solvent extracted ultrasonically, extract subjected to GPC if necessary, extract concentrated GC-MS (EPA-CLP Method) 330 pg/kg NG EPA 1987... 

Extraction of semivolatile analytes collected using modified Method 5 (Method 0010) sampling train Accelerated solvent extraction (ASE) (3545A in update IVB) Ultrasonic extraction... 

Golden, C., and E. Sawkki. Ultrasonic extraction of total particulate aromatic hydrocarbons (TpAH) from airborne particles at room temperature. Int. J. Environ. Anal. Cliem. 4 9-23, 1975. 

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