Extraction from environmental

A number of techniques have been developed for the trace analysis of siUcones in environmental samples. In these analyses, care must be taken to avoid contamination of the samples because of the ubiquitous presence of siUcones, particularly in a laboratory environment. Depending on the method of detection, interference from inorganic siUcate can also be problematic, hence nonsiUca-based vessels are often used in these deterrninations. SiUcones have been extracted from environmental samples with solvents such as hexane, diethyl ether, methyl isobutylketone, ethyl acetate, and tetrahydrofuran (THF)... 

The environmental impact of PCNs has not been extensively investigated and PCNs are not routinely measured in analytical studies of extracts from environmental samples. However, PCNs have been identified in birds of prey in Britain (69) and The Netherlands (70), in a drainage ditch in Florida, and in sediments from San Francisco Bay (71). 

Tin is readily measured in multielement analyses of air, water, and solid waste samples by inductively coupled plasma atomic emission spectroscopy. For individual analyses of tin, direct aspiration atomic absorption spectroscopy is usually used. Organotin can be extracted from environmental samples and determined by atomic spectrometric methods or gas chromatography, usually after derivatization. 

SVOCs are extracted from environmental samples with organic solvents the extracts are then concentrated to a 0.5-10 ml volume. A small volume (1-5 pi) is introduced into the injection port with a microsyringe the high temperature at which the injection port is maintained instantly vaporizes the extract without destroying the chemicals in it. 

As in other techniques, SF extracts are not always free of unwanted matrix components. A number of clean-up methods have been used with and after the extraction step to overcome this problem. Sample clean-up is mandatory with fat-soluble analytes. On the other hand, neat supercritical CO, extracts from environmental samples are often clean enough for direct injection into a gas chromatograph [17]. 

The examples described in this section 10.6.1 constituted the first report ever of ill situ reaction-extraction work involving foodstuffs. We had reported earlier on a related approach in a different field, namely a derivatisation-extraction procedure whereby phenols and methylated phenols were acetylated-extracted from environmental matrices in a one-step MAP procedure (15). The latter procedure, however, was performed under much harsher conditions that could not be used with foodstuffs where the potential of creating artefacts is a prime concern. This approach of one-pot, multiple-step procedures opens the avenue to numerous applications of direct interest to the food analysts and are especially versatile and valuable when using microwave-assisted extraction performed in open-vessel systems. This, along with solvent-less extraction (such as MAP gas-phase applications ) is believed... 

Extracts from environmental samples are seldom sufficiently free of contaminants that they can be analyzed directly, since the high-resolution columns used for GC or FIPLC analysis must not be overloaded with compounds other than the analyte. Pretreatment of the sample before GC, GC-MS, or HPLC analysis is therefore often a critical step in the analysis of extracts from complex matrices, and this is particularly important when the concentrations of... 

Analytical scale SFE was introduced by German scientists at the end of the 1970 s for the extraction of various compounds such as drugs, vitamins, and dyes using carbon dioxide as extraction media ( -iS). A major increase in analytical scale SFE applications was however first seen in the late 1980 s, when POPs were extracted from environmental samples (7), fats from food (S), and various components from polymers (9). Today SFE is a well-established extraction technique, adopted as a reference method by the U.S. EPA (10-12), and the theory and instrumentation is described in several review papers (13-17) and books (18-21). 

Analytes extracted from environmental samples are concentrated prior to measurement by evaporating the solvent, using low temperature and reduced pressure for rapid solvent removal. Volatiles in soils and sediments may be sampled directly using headspace analysis for gas chromatography. 

FIGURE 15.35 A TIC of the same standard mixture as in Figure 15.34 but spiked with 3000 ppm of mixed diesel 2/motor oil extract. This motor oil extract is typical of the low molecular weight hydrocarbons found in contaminated soil extracts from environmental samples. 

Microarrays are used for detection and quantification of the target gene using a DNA chip on which known DNA molecules are fixed. Complementary DNAs (cDNA) are reverse transcribed from RNAs isolated from culture samples, and the DNA extracted from environmental samples is hybridised to the nucleotide probes on the DNA chip. The signal intensities of these DNA-probe hybridised molecules are then detected using a fluorescence scanner. 

Prior to their separation by GC, organolead compounds need to be extracted from the sample matrix and, if necessary, derivatized into a volatile and thermally stable form. Volatile nonpolar tetraalkyl compounds can be extracted from environmental samples with nonpolar solvents such as benzene or hexane and injected directly onto the gas chromatograph. The case of nonvolatile, ionic alkyl compounds (R2Pb and RsPb ) is more complex. They should first be extracted and preconcentrated in the presence of NaCl and sodium diethyldithiocarbamate and then derivatized into a volatile form. The most widespread derivatization methods are of two distinct types those based on the use of tetraalkylborates that can be directly performed in the aqueous solution (ethylation and propylation) and those applying... 

Silicones have been extracted from environmental samples with solvents such as hexane, diethyl ether, methyl isobutylketone, ethyl acetate, and THF, using either sequential or Soxhlet techniques (690-695). Silicones of a wide range of molecular weights and polarities are soluble in THF. This feature, coupled with its volatility and miscibility with water, makes THF an excellent solvent for the extraction of silicones from wet samples, ie, soils and sediments. Trace levels of silicones extracted from environmental samples have been measured by a number of techniques, including atomic absorption spectroscopy (AA), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), pyrolysis GC-MS, as well as H and Si NMR spectroscopy (674,684,692,696-700). The use of separation techniques, such as gel permeation and high pressure liquid chromatography interfaced with sensitive, silicon-specific AA or ICP detectors, has been particularly advantageous for the analysis of silicones in environmental extracts (685,701-704). 

PCR for DGGE Anafysis The first step in DGGE analysis is DNA extraction followed by PCR amplification of a target gene. There are a number of commercially available kits for DNA extraction from environmental samples. We routinely use the bead-beating-based PowerSoil DNA Isolation Kit (MO BIO Laboratories,... 

Quantitative culture-independent methods for estimating relative abundance of gut bacteria at various taxonomic levels (usually genus, sub-genus or species level) can be divided into direct methods, based on microscopy where microorganisms are enumerated directly in environmental samples, and indirect methods, which estimate microbial relative abundance from DNA extracted from environmental samples following microbial disruption using quantitative PCR, for example. 

CA, USA), a poly(styrene-co-divinylbenzene)-based resin that is functionalized with iminodiacetic acid. Due to its high selectivity for divalent metal ions, it is predominantly used for trace metal extraction from environmental and industrial samples. On the other hand, Walsh et al. [65] used Chelex 100 as a medium for simple extraction of DNA for PCR-based typing from forensic material. 

While infrared spectrophotometry is most useful for the qualitative analysis of surfactants, various quantitative methods have been developed for well-characterized systems. For example, an attenuated total reflectance cell with a ZnSe crystal is useful for direct analysis of aqueous anionic surfactant solutions by FTIR, while avoiding the deleterious effects of water on the usual transmission cells. In this case, the sulfonate absorbance at 1175 cm" , or the sulfate absorbance at 1206-1215 cm , is used for quantification (10,26). In another application, the weak absorption bands in the 1429-1333 cm" region are used to measure the relative amounts of linear and branched chain alkylbenzene sulfonates extracted from environmental waters (27). This is the one advantage of the infrared technique over those that have supplanted it for wastewater analysis its ability to differentiate the straight and branched chain compounds (28). No procedure will be given here, since the cleanup prior to IR analysis can be handled adequately by the method for LAS analysis by desulfona-tion/gas chromatography, described in Chapter 8. 

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