Organochlorines quantification

GC is coupled with many detectors for the analysis of pesticides in wastewater. At the present time the most popular is GC-MS, which will be discussed in more detail later in this section. The flame ionization detector (FID) is another nonselective detector that identifies compounds containing carbon but does not give specific information on chemical structure (but is often used for quantification because of the linear response and sensitivity). Other detectors are specific and only detect certain species or groups of pesticides. They include electron capture,nitrogen-phosphorus, thermionic specific, and flame photometric detectors. The electron capture detector (ECD) is very sensitive to chlorinated organic pesticides, such as the organochlorine compounds (OCs, DDT, dieldrin, etc.). It has a long history of use in many environmental methods,... 

GC-MS can be used to analyze organochlorine pesticides, for example, a-, [3-, y-HCH, HCB, and polychlorinated biphenyls (PCB). The components are quantified by using an internal standard. Furthermore, a calibration is performed with a standard mixture containing known concentrations of the components to be measured and one or more components not contained in the sample (internal standards). The calibration is followed by injection of the sample containing known amounts of internal standards. Quantification is relative to the internal standard. In this way, the sample extract volume will not be included in the calculations, and it is not necessary to accurately determine the final sample volume after evaporation of the injection volume. The GC-MS instrument should be calibrated every day. The sensitivity of the mass spectrometer can, for instance, be controlled daily by determining the signal-to-noise ratio for a given amount of a chosen component (PCB-101 could be one such component). For further details of the method, the reader is referred to different manuals and papers on the subject.417... 

Finally, even if most of the pesticides worldwide are used in fruit and vegetable crops, data on pesticide residues in animal products are also essential, taking into account that livestock can be easily exposed to pesticides directly or through residues in their feed. For instance, the 2009 European Union Report revealed the presence of 34 different pesticides in animal products [115]. Garcfa de Llasera et al. [128] revealed the presence of chlofenvinphos and chlorpyrifos in liver samples, whereas a-endosnlfan, endosulfan sulfate, and dichloran have been reported in pork and lamb samples (<10 pg/kg) [129]. Bolafios et al. [130] studied the occurrence of organochlorine pesticides and polychlorinated biphenyls in chicken eggs. Benzene hexachloride and 28 polychlorinated biphenyl were detected in only one of the 30 samples at concentrations of 15 and 10 ng/g, respectively. However, five samples also contained traces of OC and PCB residues, even if at concentration levels below the limit of quantification. Einally, a-endosulfan and P-endosulfan were found in commercial milk-based infant formulas at concentration levels from 1.18 to 5.03 pg/kg [35]. The same study also showed the presence of fenitrothion, chlorpyrifos ethyl, and bifenthrin at maximum concentrations of 0.23,1.30, and 0.68 pg/kg, respectively. 

The electrochemical biosensors for pesticides monitoring involve enzyme, antibodies, and cells-based sensors [7, 24, 27, 30, 32]. The application of various enz3mes - acetylcholinesterase, acid phosphatase, alkaline phosphatase, organo-phosphoms hydrolase, and tyrosinase - for the quantification of organochlorine, organophos-phate, and carbamate pesticides in the environment... 

SPE is also an efficient procedure for recovery of organochlorine (Sherma, 1988b) and organophosphorus (Sherma and Bretschneider, 1990) pesticides from water and can be combined with the TLC procedures described in Experiment 3 for quantification of these compounds in water. SPE and TLC have also been used to quantify the benzoylurea insecticide diflubenzuron in water (Sherma and Rolfe, 1993). 

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