Extract cleanup

Air Collect on hexylene glycol-alumina adsorbent sampler extract cleanup with Florisil GC/FPD 0.1 ng/m 53.4 Stanley et al. 1971... 

Analysis of methyl parathion in sediments, soils, foods, and plant and animal tissues poses problems with extraction from the sample matrix, cleanup of samples, and selective detection. Sediments and soils have been analyzed primarily by GC/ECD or GC/FPD. Food, plant, and animal tissues have been analyzed primarily by GC/thermionic detector or GC/FPD, the recommended methods of the Association of Official Analytical Chemists (AOAC). Various extraction and cleanup methods (AOAC 1984 Belisle and Swineford 1988 Capriel et al. 1986 Kadoum 1968) and separation and detection techniques (Alak and Vo-Dinh 1987 Betowski and Jones 1988 Clark et al. 1985 Gillespie and Walters 1986 Koen and Huber 1970 Stan 1989 Stan and Mrowetz 1983 Udaya and Nanda 1981) have been used in an attempt to simplify sample preparation and improve sensitivity, reliability, and selectivity. A detection limit in the low-ppb range and recoveries of 100% were achieved in soil and plant and animal tissue by Kadoum (1968). GC/ECD analysis following extraction, cleanup, and partitioning with a hexane-acetonitrile system was used. 

The natural matrix materials, which are similar to the actual environmental, clinical, food, or agricultural samples analyzed, are used to validate the complete analytical measurement process including extraction, cleanup and isolation procedures, and the final chromatographic separation, detection, and quantification. 

Validation of the complete analytical procedure (induding solvent extraction, cleanup of the extracts, isolation of the analytes of interest, and chromatographic separation and detection) requires the use of CRMs with matrices similar to those... 

After sampling, homogenization, extraction, cleanup, concentration and possible derivatization, use a suitable determination method which provides sufficient selectivity or specificity and sufficient sensitivity. 

Both multi-residue methods are presented in several parts, which separate general considerations from procedures for extraction, cleanup and determination/ confirmation. Whereas in EN 12393 several extraction and cleanup steps cannot be combined arbitrarily, the modular concept is utilized to a greater extent in EN 1528. In the latter standard, there is no limitation to the combination of several extraction procedures, mostly designed for different commodities, e.g., milk, butter, cheese, meat or fish, with different cleanup steps. Both standards, EN 1528 and EN 12393, do not specify fixed GC conditions for the determination and confirmation. All types of GC instruments and columns, temperature programs and detectors can be used, if suitable. 

Extraction), cleanup Specificity of At LCL Response obtained from the Whenever possible tested by Comparison of relative... 

The only published immunoassay method submitted to date to EPA OPPTS as an enforcement method for a range of substrates (water, sediment, crops, processed crop fractions, and animal tissues) is the spinosad method, developed by Young et al. This method uses the spinosad RaPID Assay (Strategic Diagnostics) for determination of total spinosad residues (TSR). This discussion will be limited to crop and animal tissues, because the water and soil analyses are analogous to the triasulfuron method. The extraction, cleanup, and method parameters are summarized in Table 2. 

Most modern methods of analysis to determine pesticide residues in food commodities, whether a multi-residue method (MRM) or a single-residue method (SRM), can be broken down into three or four basic steps sample processing, sample extraction, extract cleanup (optional) and instrumental determination. 

Trace analysis of soil samples often requires post-extraction cleanup to remove coextracted matrix interferences. There are several difficulties that may arise during chromatographic analysis due to interferences present in sample extracts. To avoid these and other issues, one or more of the following cleanup techniques are often used. 

Principles and Characteristics Because of the limited selectivity of extraction, a chromatographic analysis is almost always needed. Recently, a fair amount of progress has been made regarding the front end of the total analysis procedure, namely the integration of sample preparation (this being the analytical bottleneck) and separation. The idea behind such systems is to perform sample extraction, cleanup and concentration as an integral part of the analysis in a closed system. Scheme 7.2 shows the main procedures related to sample preparation for chromatographic analysis. 

Whereas the use of conventional fast atom bombardment (FAB) in the analysis of polymer/additive extracts has been reported (see Section 6.2.4), the need for a glycerol (or other polar) matrix might render FAB-MS analysis of a dissolved polymer/additive system rather unattractive (high chemical background, high level of matrix-, solvent- and polymer-related ions, complicated spectra). Yet, in selected cases the method has proved quite successful. Lay and Miller [53] have developed an alternative method to the use of sample extraction, cleanup, followed by GC in the quantitative analysis of PVC/DEHP with plasticiser levels as typically found in consumer products (ca. 30 %). The method relied on addition of the internal standard didecylphthalate (DDP) to a THF solution of the PVC sample with FAB-MS quantitation based on the relative signal levels of the [MH]+ ions of DEHP and DDP obtained from full-scan spectra, and on the use of a calibration curve (intensity ratio m/z 391/447 vs. mg DEHP/mg DDP). No FAB-matrix was added. No ions associated with the bulk of the PVC polymer were observed. It was... 

A cleanup column from a commercial source can be used or can be constructed easily from a Pasteur pipette (see Figure 12.12). A small piece of cotton is placed in the bottom of the pipette. A suitable absorbant, such as a solid coated with or bonded to a high-molecular-weight hydrocarbon such as octadecanol (this is often simply called a C-18 extraction column), can be loaded into the pipette and covered with another small amount of a cotton ball. A list of common extract cleanup absorbants and their characteristics is given in Table 12.3. 

TABLE 123. Some Common Extract Cleanup Adsorbents... 

Dqbrowska H, Dqbrowski L, Biziuk M, Gaea J, Namiesnik J. Solid-phase extraction cleanup of soil and sediment extracts for the determination of various types of pollutants in a single run. J. Chromatogr. A 2003 1003 29-42. 

A number of techniques have been developed to directly volatilize soil components and contaminants and introduce them into the carrier gas of a gas chromatograph. Such procedures avoid the time and cost of extraction, cleanup, and concentration and also avoid the introduction of contaminants during the extraction process. However, these methods are not universally applicable and caution must be used when applying new or untested analyses or analytical procedures [2-5],... 

Lopez-Avila et al. [59] used microwave assisted extraction to assist the extraction of polyaromatic hydrocarbons from soils. Another extraction method was described by Hartmann [60] for the recovery of polyaromatic hydrocarbons in forest soils. The method included saponification of samples in an ultrasonic bath, partitioning of polyaromatic hydrocarbons into hexane, extract cleanup by using solid-phase extraction, and gas chromatography-mass spectrometric analysis using deuterated internal standards. Polyaromatic hydrocarbons were thermally desorbed from soils and sediments without pretreatment in another investigation [61]. 

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