Sample matrix sediments

In order to select the instmmental conditions for carrying out the ATR measurements several parameters including the number of accumulated scans per spectra or nominal resolution were tested. To avoid the crosscontamination and to establish an appropriate strategy for cleaning the ATR cell between samples, several procedures were tested using background and blank controls. Moreover, the possible sample sedimentation on the ATR plate cell due to the complexity of the sample matrix during the spectra acquisition was also checked. 

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. 

Also consider the use of NIST sediments 1646, 2704, and soils 2709-2711 in exploration geochemistry. These samples were certified largely in view of the demand for samples to support monitoring of toxic elements in environmental samples. However, many of the elements certified overlap either the list of primary ore elements or the list of pathfinder elements. Thus, these samples may legitimately be used in a very different application than the one that prompted certification. The sample matrix is ideal for the alternative application, and so is the suite of certified elements. 

Standard analytical techniques for sampling and pretreatment and analytical requirements for sediment studies are less available than for water and soil studies. To obtain meaningful results from laboratory experiments, the sediment samples should be kept in the original aqueous matrix, and analyses should be carried out immediately to minimize changes to the sample matrix due to chemical and biological processes that could occur during storage. 

PCBs in biological samples are usually extracted by a Soxhlet column and with a nonpolar solvent such as hexane. The sample is first mixed with sodium sulfate to remove moisture. The extraction of PCBs from sediments was tested with sonication, with two sonications interspersed at a 24-h quiescent interval, with steam distillation, or with Soxhlet extraction (Dunnivant and Elzerman 1988). Comparison of the recoveries of various PCB mixtures from dry and wet sediments by the four techniques and the extraction efficiency of four solvents showed that the best overall recoveries were obtained by Soxhlet extraction and the two sonication procedures. In comparisons of solvent systems of acetone, acetonitrile, acetone-hexane (1+1), and water-acetone-isooctane (5+1.5+1), recoveries of lower chlorinated congeners (dichloro- to tetrachloro-) were usually higher with acetonitrile and recoveries of higher chlorinated congeners (tetrachloro- to heptachloro-) extracted with acetone were superior (Dunnivant and Elzerman 1988). The completeness of extraction from a sample matrix does not seem to discriminate against specific isomers however, discrimination in the cleanup and fractionation process may occur and must be tested (Duinker et al. 1988b). 

After collection, samples were divided into 5-cm sections or into sections determined by changes in sample matrix. Only sediment from the interior of the core (not in contact with the corer) was used to avoid possible contamination from the polycarbonate and from sediment fines forced along the wall of the tube. Sectioned samples were stored in solvent-rinsed bottles at 4 °C until analyzed. Some samples used in this study were collected from reaches of the submerged riverbed (where PCBs were deposited before the reservoir was filled). Sample locations (Figure 1) were determined in relation to buoys placed and maintained by the U.S. Army Corps of Engineers. Samples used in this study were limited to those found to be contaminated with at least 1 xg/g of total PCB to minimize quantification error during weight-percent calculations. 

A study to explore the effect of the sample matrix in SFE was done with a set of polychlorinated biphenyl (PCBs) and a river sediment matrix. Figure 12 shows the on-line SFE/GC characterization of a PCB standard ranging from monochloro to decachlorolbiphenyl compounds present at concentration levels from 5 to 100 microgram per milliliter. An election capture GC detector (ECD) was used for the determination of these PCB s. Since this PCB standard was made up in liquid... 

Sequential extraction involves treatment of a sample of soil or sediment with a series of reagents in order to partition the trace element content. The reagents used are generally similar to those employed as single extractants to liberate metals bound to particular components of the sample matrix, discussed above. The growth in popularity of the approach is demonstrated by the marked increase in publications in which it has featured over the past decade (Fig. 10.2). 

Four types of extraction procedures are employed in these analyses depending on the sample matrix. Chemical waste samples are extracted by refluxing with a Dean Stark water separator. Fly ash samples and soil/sediment samples are extracted in a combination of a Soxhlet extractor and a Dean Stark water separator. Water samples are filtered and then the filtrate is extracted using either a separatory funnel procedure or a continuous liquid-liquid extraction procedure. The filtered particulates are extracted in a combination of a Soxhlet extractor and a Dean Stark water separator. 

When the slurry itself is to be fed to the atomizer or vaporizer, the duration of the previous ultrasonication step is dictated by the nature of the sample matrix. Thus, samples for the determination of As, Pb, Se and Sn in sediments by electrothermal vaporization... 

Characterisation of the Sample Matrix for Determinations in Sediments (All Types of... 

CHARACTERISATION OF THE SAMPLE MATRIX FOR DETERMINATIONS IN SEDIMENTS (ALL TYPES OF CHEMICAL)... 

In the analytical scheme, besides the sampling and the final analysis, the sample preparation and cleanup are also crucial. Sample preparation plays an important role in the analysis of FRs in environmental samples because of the complex matrices and only trace levels of analytes. Solid and semisolid samples are usually first dried and homogenized. Then the FRs are extracted from the sample (solid or liquid), and the extract is usually purified, fractionated, and concentrated before the final analysis, which is typically performed with gas or liquid chromatography. The extraction procedure is dependent on the sample matrix different methods are used for sediment, tissue, and liquid samples. After extraction, it will usually be necessary to purify and fractionate the extract, because most extraction methods are insufficiently selective and the separation power of the analytical technique not sufficient. Extracts typically contain several analytes similar to the FRs, which may be present in much higher quantities. The fractionation procedures are similar for the different types of extracts. Typical analytical procedures are given in Tables 31.2 to 31.6. 

Soil, sediment, and sewage sludge samples require highly efficient methods of extraction, because the analytes tend to be very tightly bound to the sample matrix. 

The errors associated with the steps identified in Section 12.13.5.1 have been discussed and the approaches used to establish and combat them will now be summarized. For the extraction step, QA considerations mean the extraction efficiency needs to be validated and this can be done either by spike recovery experiments or by using a representative CRM. The main criticism of spike recovery experiments is that the spike is not bound in the sample matrix in the same way as the naturally occurring analyte being measured. However, if a low recovery is apparent using the method chosen, it would indicate an inadequate protocol or one that requires further developmental work. The range of CRM available with values for some of the more important chemical species is increasing, and includes various sediments, fish and shellfish tissue, and human matrices such as hair and urine. However, real samples are rarely identical to the matrix CRM available, so care should be taken when validating methods to be used for real samples. 

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