Extraction and Clean-up Methods

New methods have been introduced for the extraction and clean-up of PFCs in both biological and environmental samples. Primarily these methods have focused on solid phase extraction (SPE) for fluid samples, and accelerated liquid extraction or liquid-solid extraction methods for solid samples [97]. The extraction media of choice is dependent on the polarity of the PFCs to be analysed. Typically, moderately polar media such as Oasis WAX SPE or methanol and acetonitrile are employed for extraction of shorter chain (C4 to Cg) PFSAs and PFCAs, while less polar or nonpolar SPE media such as Cig and Oasis HLB are employed for the longer chain PFSAs and PFCAs [97]. Neutral PFCs have been extracted using both nonpolar media such as Cig SPE or hexane and moderate polar such as Oasis HFB and WAX SPE, a hexane-acetone mixture or acetonitrile [97]. 

Air sampling media has been extracted using different solvent systems. Both particulate and gas phase extracts have been extracted using methanoFethyl acetate [99, 100, 102], while other studies have employed petroleum ether/acetone for extraction of the PUF/XAD and dichloromethane for the filter [101]. Generally extracts are filtered prior to analysis. Some researchers have also included a clean-up step. For example, Shoeib, Hamer and Vlahos [101] passed PUF/XAD sample extracts through an alumina column and eluted with dichloromethane in ethyl acetate, prior to the analysis of FTOHs and FSAs. 

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The extraction and clean-up methods used for the recovery of organophosphorus derivatives do not differ basically from those applied to other groups of substances. However, because of the high toxicity of the compounds involved, the techniques must be extremely sensitive and able to detect sub-nanogram amounts. A number of reviews have been published on the subject164-171. As previously mentioned, the compounds to be analysed may be found in living matter as well as in soil, sediments, water and air the experimental methods vary accordingly. 

Codina, G., Vaquero, M. T., Cornelias, L., and Broto-Puig, F., Comparison of various extraction and clean-up methods for the determination of polycyclic aromatic hydrocarbons in sewage sludge-amended soils, J. Chromatogr. A, 673, 21-29, 1994. 

Lino, C.M. and Noronha da Silveira, M.I. 1997. Extraction and clean-up methods for the determination of organochlorine pestieide residues in medicinal plants. J. Chromatography A, 769, 275-283. 

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

Then, the extraction and clean-up stages can be tailored to meet the requirements of the particular detector being used. We can now consider some techniques used at the final separation and detection stages and discuss criteria which enable a decision to be made about which technique is the most appropriate. So often, experts in a particular technique believe that their technique can solve all of the world s problems. It may well be able to detect the analyte in question, but is it the most suitable method of detecting that analyte in the given matrix ... 

Alford Stevens et al. [49] carried out a multi-laboratory study of automated gas chromatography-mass spectrometric determinations of polychlorinated biphenyls in soil. The influence of various factors on the accuracy of analytical results were studied. Shaker extraction for 12.5h followed by Florisil chromatography were demonstrated to be the most reliable methods for extraction and clean-up. 

Pretreatment of biological samples for surfactant analysis is usually straightforward and includes either homogenising with anhydrous sodium sulphate or freeze-drying. Below, the sample treatment methods for extraction and clean-up of non-ionic and anionic surfactants in biota that have been encountered in the literature are reviewed. 

Multi-residue schemes are used by a number of workers for the determination of very different compounds [189, 402, 405, 453, 454, 474, 478, 480, 481] and each of the methods of extraction and clean-up discussed in the earlier part of this chapter have been incorporated into an overall analytical scheme. At present the on-line approach is difficult to incorporate fully into the multiresidue scheme [189,479] in which a large number of compounds are separated... 

Recent trends in pesticide analysis in food aims for reduced sample pretreatments or simplified methodologies (as QuEChERS approaches), the use of online purification processes, the use of new adsorbents (such as molecular imprinted polymers (MIPs) and nanomaterials) for the extraction and clean-up processes, and focused on the development of large multiresidue methods, most of them based on LC-MS/ MS. In spite of the relevant role of LC-MS/MS, GC-MS-based methods still play an important role in pesticide analysis in food. Despite the development achieved in the immunochemical approaches, the need for multi-residue methods has supported the development and use of instrumental techniques. 

Modem extraction and clean-up techniques, such as pressurised liquid extraction and microwave-assisted extraction, have almost not applied to the analysis of PFCs yet. Llorca et al. [49] reported the development and application of a PEE method for PFCs determination in fish. This technique provided rapid and accurately clean extracts for sensitive analysis. 

Advisable for methods including a complex sample preparation procedure like extraction and clean-up... 

Sample extraction and clean-up -solid methods recommended by EPA for the specific matrix specific matrix... 

The infralaboratory calibration study was performed by the Institute for Environmental Studies. Sediment was extracted and cleaned up as indicated here. The determination of dioxin and/or dioxin-like content was according to the method indicated under the section DR CALUX analysis. For the intralaboratory study, the following parameters were investigated limit of detection (LOD), limit of quantitation (LOQ), and reproducibility and repeatability of the bioassay. 

Traditional microbial screening methods have insufficient sensitivities to meet new regulations and classical physicochemical techniques, such as chromatographic methods and mass spectrometry which are often precluded due to the level of experience, skills, and cost involved. Moreover, these methods require laborious extraction and clean up steps that increase analysis time and the risk of errors. 

OP compounds and carbamate are widely used as insecticides, pesticides, and warfare agents [20,21], Detection of pesticides is usually carried out by multiresidue methods (MRMs) of analysis, which are able to detect simultaneously more than one residue and have been developed mainly based on chromatographic techniques. Two groups of MRMs are used (i) multiclass MRMs that involve coverage of residues of various classes of pesticides, and (ii) selective MRMs, which concern multiple residues of chemically related pesticides (e.g., IV-methyl carbamate pesticides (NMCs), carboxylic acids, phenols, etc.). As foods are usually complex matrices all of the pre-analytical steps (matrix modification, extraction, and clean-up) are often necessary. 

Fish, birds, seals (CDDs) No methods details extraction and clean-up on silica, modified silica, and alumina columns used internal standards added HRGC/LRMS (EI/SIM) HRGC/LRMS (NCI/SIM) 1-50 pg 0.01-0.1 pg No data Buser et al. 1985... 

Chemical analysis of hair samples may also provide a method for examining chronic mycotoxin exposures. In 2003, Sewram et al. (2003) reported that human hair testing could be used to detect fumonisins. After extraction and clean up, high performance liquid chromatography coupled to electrospray ionization-mass spectrometry (HPLC-ESI-MS) was able to detect fumonisin Bi, fumonisin B2, and fumonisin B3 from human hair samples (Sewram et al., 2003). However, these were... 

Extraction and clean-up techniques for the analysis of PBDE residues in biological samples are similar to those developed for PBB. Table 6 shows several methods to determine PBDEs in various media. Most methods are based on extraction with organic solvents, purification of the extracts by gel permeation or... 

One of the first laboratory groups to apply paper chromatography as an identification and estimation technique was that of Muller et al. (iO). In 1957, at the Control Laboratory in Basel, his group developed an extraction and clean-up procedure for a few organochlorine and or-ganophosphorus insecticides and then determined the quantity of residue with reverse phase paper chromatography. Similar procedures were followed by McKinley and Mahon in Canada (ii) and Mills in the United States (12). This first series of papers triggered wide applications of paper methods for residue determinations (13, 14, 15, 16, 17, 18, 19, 20, 21, 22). 

Limited data were located regarding methods for detecting the hydrocarbon components of gasoline in biota (bivalve mollusks) (Dimock et al. 1980). The methods used were GC (detector not reported) and GC/MS. Sample preparation included tissue digestion, extraction and clean-up, and solvent exchange to hexane. Recovery was poor (-60%). Sensitivity and precision were not reported. 

The validation has the objective to identify, during the method development process, all sources of error and eliminate them or to quantify their contribution to the total uncertainty of the determination. For trace organic determinations particular attention must be given to the quantitative extraction and clean-up of all PCBs. Several types of adapted materials must be prepared to test all steps of the process (from simple calibrant solutions or mixtures, spiked extracts, to spiked soil material). CRMs should be used for validating trueness. Laboratory RMs must be prepared for the establishment of control charts when the method is under statistical control. 

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