Environmental pollutants sample preparation

Various liquid chromatographic techniques have been frequently employed for the purification of commercial dyes for theoretical studies or for the exact determination of their toxicity and environmental pollution capacity. Thus, several sulphonated azo dyes were purified by using reversed-phase preparative HPLC. The chemical strctures, colour index names and numbers, and molecular masses of the sulphonated azo dyes included in the experiments are listed in Fig. 3.114. In order to determine the non-sulphonated azo dyes impurities, commercial dye samples were extracted with hexane, chloroform and ethyl acetate. Colourization of the organic phase indicated impurities. TLC carried out on silica and ODS stationary phases was also applied to control impurities. Mobile phases were composed of methanol, chloroform, acetone, ACN, 2-propanol, water and 0.1 M sodium sulphate depending on the type of stationary phase. Two ODS columns were employed for the analytical separation of dyes. The parameters of the columns were 150 X 3.9 mm i.d. particle size 4 /jm and 250 X 4.6 mm i.d. particle size 5 //m. Mobile phases consisted of methanol and 0.05 M aqueous ammonium acetate in various volume ratios. The flow rate was 0.9 ml/min and dyes were detected at 254 nm. Preparative separations were carried out in an ODS column (250 X 21.2 mm i.d.) using a flow rate of 13.5 ml/min. The composition of the mobile phases employed for the analytical and preparative separation of dyes is compiled in Table 3.33. 

HPLC instrumentation and column technology have undergone major advances since the early 1970s, when HPLC made its debut in the field of vitamin analysis. Yet sample preparation in food analysis continues to rely largely on manual wet-chemical techniques, which are time consuming and labor intensive, require considerable analytical skill, and constitute the major source of error in the assay procedure. There is also the serious problem of environmental pollution and the exposure of laboratory personnel to toxic chemicals. 

The analysis of chemical pollutants in the environmental matrices has entered a new phase in the last decade. Modifications in instrumentation, sampling, and sample preparation techniques have become essential to keep up with the requirements of achieving ppt to low ppb detection levels, as well as to achieve a faster speed of analysis. In addition, more stringent quality-control (QC) requirements in analytical methods have become necessary to obtain high data quality. This has led to the many new methodologies that are different from the conventional macro and semicmicro analytical approach. 

Sample preparation is a key step in all environmental analyses. Two major areas of development in this area have been solid phase extraction and supercritical fluid extraction. Both techniques have made the extraction of pollutants from aqueous and nonaqueous matrices relatively simple, fast, and less expensive. These processes, along with gel permeable chromatography, provide efficient methods of removing interferences. 

The possibility of including ecotoxicological studies in the monitoring of environmental pollution should therefore be considered. Beforehand, however, an appropriate classification of environmental samples will need to be prepared, a suitable ecotest chosen, and implementation tests conducted. 

The techniques of sample preparation, extraction (isolation), and/or preconcentration of analytes are usually applied in the analysis of trace components of gaseous, liquid, and solid samples. During this operation, transport of analytes from primary matrices (donors) to the secondary matrix (the acceptor) takes place. It should be remembered, however, that the extraction and preconcentration steps could be a source of environmental pollution. The techniques of sample preparation introduced in this chapter have the following advantages253 ... 

Steroids hormones as environmental pollutants Analysis of steroids as environmental endocrine disrupting compounds sample preparation, e.g., LLE vs. SPE immunoassay vs. GC-MS/ MS and LC-MS/MS analyses sensitivities, e.g., LOD at pg-ng/mL level. [13]... 

Membrane Techniques The interest in membrane techniques for sample preparation arose in the 1980s. Extraction selectivity makes membrane techniques an alternative to the typical sample enrichment methods of the 1990s. Different membrane systems were designed and introduced into analytical practice some more prominent examples are polymeric membrane extraction (PME), microporous membrane liquid-liquid extraction (MMLLE), and supported liquid membrane extraction (SEME) [106, 107]. Membrane-assisted solvent extraction (MASE) coupled with GC-MS is another example of a system that allows analysis of organic pollutants in environmental samples [108-111] ... 

As in other areas of analysis, HPLC is a useful complementary technique to GLC in analyzing pollutants in the environment. An advantage of HPLC in environmental analysis is that molecules of varying polarity (e.g. pesticide + metabolite mixtures) can be analyzed in one chromatographic run. Since aqueous mobile phases can be used in reversed-phase HPLC (including ion-pair partition modes) sample preparation is often less extensive than in GLC. The number of clean-up steps can also be reduced by the use of a precolumn to protect the analytical column or by a preliminary size separation of a crude extract on an exclusion column. 

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