Soxtec extraction

G.C. Mattem, C.I. Nuessle, D.L. Green, W.M. Leimkuehler, J.D. Philpot, RJ. Ness, and K.S. Billesbach, Accelerated field residue analysis of tebuconazole using Soxtec extraction and HPLC/electrospray tandem mass spectrometry (HPLC/ESI-MS-MS), Presented at the Midwest Regional Meeting of the American Chemical Society, Osage Beach, MO, October 29, 1997. 

Applications Caceres et al. [114] compared various methods for extraction of Tinuvin 770 and Chimas-sorb 944 from HDPE pellets, namely room temperature diffusion in CHC13 (20 % extraction), ultrasonica-tion (20% extraction), Soxtec extraction with DCM (nonsolvent) (50 % extraction), dissolution (dichloroben-zene)/precipitation (2-propanol) (65-70% recovery) and boiling under reflux with toluene (solvent) at 160 °C (95 % extraction). By changing conditions (nature of solvent, T, t) similar comparisons do not have much added value. Table 3.6 compares the results of reflux extraction and MAE for additives in LDPE [115]. 

Figure 3.2 The three-step Soxhlet extraction process of the Soxtec extraction system (a) solubilisation of extractable matter from sample immersed in boiling solvent (b) rinsing of extracted solid and (c) concentration of extracted sample and collection of distilled solvent for reuse or disposal. Reproduced by permission of FOSS Analytical A/S, Hillerdd...

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]. 

Lopez-Avila V, Bauer K, Milanes J, et al. 1993. Evaluation of Soxtec extraction procedure for extracting organic compounds from soils and sediments. J AOAC International 76 864-880. 

Lopez-Avila et al. [8] published a study in 1993 that evaluated the Soxtec extraction of 29 target compounds (seven nitroaromatic compounds, three haloethers, seven chlorinated hydrocarbons, and 12 organochlorine pesticides) from spiked sandy clay loam and clay loam. Among the five factors investigated (matrix type, spike level, anhydrous sodium sulfate addition, total extraction time, and immersion/extraction time ratio), matrix type, spike level, and total extraction time had the most pronounced effects on method performance at the 5% significance level for 16 of the 29 target compounds. The two solvent mixtures, hexane-acetone (1 1) and methylene chloride-acetone (1 1), performed equally well. Four compounds were not recovered at all, and apparently were lost from the spike matrix. Limited experimental work was performed with 64 base-neutral-acidic compounds spiked onto clay loam, and with three standard reference materials certified... 

Extract with methylene chloride evaporate to and dissolve ppb) residue in alkaline methanol/water Soxtec extraction of clay loam using hexane acetone (1 1). Reduce volume... 

The current methods used for the determination of fat in meat and meat products include tedious Soxhlet and Soxtec extractions (AOAC method 991.36) - which suffer from being time, energy and solvent consuming techniques - and an automated method that uses microwaves to dry the sample before extracting the dried sample with solvent while agitating it mechanically [17, 18]. All these methods have in common the requirement that the sample must be dry because efficient permeation of the solvent is hindered by residual moisture, hence decreasing the abihty to dissolve the fat. 

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. 

Soil samples are extracted with methanol-water (7 3, v/v) using a Soxtec extractor. After addition of an isotopically labeled internal standard (IS) and dilution to 50 mL, the extracts are analyzed by electrospray LC/MS/MS. 

Extraction thimbles, Soxtec (Tecator) or equivalent Filter aid, Celite 545 (Fisher Scientific) or equivalent... 

Washing/soakinga Shake-flask extraction12 In-vial LSEa Reflux extraction Soxhlet/Soxtec /Soxtherm extraction... 

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 ,... 

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],... 

Principles and Characteristics In boiling under reflux procedures a small amount of ground polymer (typically 3g) is placed in a headspace jar (typically 100 mL) and solvent (typically 30 mL) is added. After sealing, the jar is placed in an oven at a temperature where the solvent slowly refluxes. The solvent is, therefore, at the highest temperature possible without applying an external pressure. Consequently, reflux extractions tend to be much faster than Soxhlet extractions. Examples are Soxtec , Soxtherm , FEXTRA and intermittent extraction. Whilst, in theory, partitioning of the analyte between the polymer and solvent prevents complete extraction, this hardly ever constitutes a problem in practice. As the quantity of solvent is much larger than that of the polymer, and the partition coefficients usually favour the solvent, very low additive levels in the polymer result at equilibrium. Any solvent or solvent mixture can be used. 

Applications Although Soxtec combines the best qualities of reflux and Soxhlet extractions up to now fairly little evidence has been reported concerning the efficacy of this system for polymer and rubber analysis. Nevertheless, it appears that oligomers and other reaction residues, softeners, antioxidants (e.g. BHT) and several other additives used to modify polymers are easily extracted from PVC, PP, PE, PS, rubber and many other polymeric materials. Also, some leading international plastic, rubber and packaging companies have made Soxtec an integral part of their quality control routines. Some application examples where Soxtec has proved successful are [148] ... 

Table 3.4 contains a comparison of microwave extraction with other sample preparation procedures. MAE compares favourably with Soxhlet/Soxtec and... 

S, Soxhlet S , Soxtec R, reflux SF, shake-flask US, ultrasonics SFE, supercritical fluid extraction MAE, microwave-assisted extraction PFE, pressurised fluid extraction (ASE , ESE ) D/P, dissolution/precipitation. 

Tecator [34] has described an apparatus, the Soxtec System HT6, for the organic solvent extraction of organics from soils preparatory to further analysis. 

The most commonly used solvent for the extraction of both alkylphenols and APEO is methanol [15-19]. If sodium hydroxide (20%, w/w) is added to the methanol, recoveries may increase by 25% [16,20]. Nonylphenoxy carboxylates (NPECs) can also be extracted using Soxhlet with methanol, but recoveries are often below 50% [19]. Only one method similar to Soxhlet has been reported for the extraction of AEOs, in which a Soxtec system with methanol is used [18]. 

Soxhlet extraction and automated Soxhlet extraction are described in this section. Soxhlet extraction was named after Baron Yon Soxhlet, who introduced this method in the mid-nineteenth century. It had been the most widely used method until modern extraction techniques were developed in the 1980s. Today, Soxhlet is still a benchmark method for the extraction of semivolatile organics from solid samples. Automated Soxhlet extraction (Soxtec being its commercial name) offers a faster alternative to Soxhlet, with comparable extraction efficiency and lower solvent consumption. 

Figure 3.2. Schematic diagram of an automatic Soxhlet extraction device (Soxtec).

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. 

A fuUy automated Soxhlet extraction has been patented as Soxtec by Foss Tecator (Sweden) based on a four-step solvent extraction technique. The sample is rapidly dissolved during the first step in boiling solvent. The remaining soluble matter is efficiently removed at the second step, whUe distilled solvent is collected at the third step. In the fourth step, the sample cup lifts off the hot plate, utilizmg residual heat to predry while eliminating boil-dry risk. 

Randall, E.L., Crude Fat, Hexanes Extraction, in Feed Cereal Grain and Forage (Randall/Soxtec/SubmersionMethod) Collaberative Study J.A.O.A.C., 1974, 57(5), 1165. 

Freeze-dried samples were submitted to a two-stage extraction in a Soxtec System HT6 Tecator (France) with 77... 

A faster variant of the Soxhlet method using less solvent (40 ml instead of 200 to 300 ml) was developed under the generic name Soxtec. The extraction time with this technique drops from 16 h (for Soxhlet extraction) to 3 h. 

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