Organophosphate compounds, detection

Six different individual data matrices were obtained for GW (gwi, gw2,..., gw6) but, in this case, rows (samples) were not common for all data matrices. A new GW data matrix was obtained after individual matrix concatenation containing 92 samples in total (see Fig. 7). In this case, the number of samples for the different sampling campaigns was not coincident (10, 16, 17, 15, 17, and 17 locations were sampled, from first to sixth campaigns respectively). Seven variables (all of them detected in SW as well) were measured in every GW sample an organophosphate compound (tributylphosphate), triazines (atrazine, desethylatrazine, simazine, and terbuthylazine), and APs (octylphenol and nonylphenol). 

Finally, three additional individual data matrices were obtained for soil (so1 so2, and so3), in this case with the same number of samples (rows) for each of them. A new soil data matrix (SO) was obtained after individual matrix concatenation containing 36 samples in total (12 samples analyzed in 3 sampling campaigns) (see Fig. 7). Fifteen variables (all of them detected in SE as well) were measured in every sample PAHs (acenaphtylene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(a)pyrene, indeno (l,2,3-cd)pyrene, dibenzo(a,h)anthracene, and benzo(g,h,i)perylene), an organophosphate compound (tributylphosphate), and an OC (4,4 -DDE). 

Relatively Httle is known about industrial organophosphates, such as triphenyl phosphate, trioctyl phosphate, and tris(chloropropyl) phosphate. These compounds are used as plasticizers and flame retardants and are likely to reach the marine environment. Six organophosphates were detected in the water of Osaka Bay in concentrations ranging from 0.1 pg/1 to 1.3 pg/1. The compounds tris(2-chloroethyl)phosphate and tributyl phosphate were the most abundant [144]. 

As reversible, competitive inhibitors of enzymes, porphyrins can be used for identification and quantification of a substrate or other competitive inhibitors of enzymes. This approach has been successful in the development of cholinesterase and organophosphorus hydrolase bearing glass surfaces for the detection of substrates and inhibitors, including organophosphate compounds. The technique has demonstrated detection limits for sarin (GB) below the Immediately Dangerous to Life or Health levels mdicated by CDC/NIOSH. 

Enzymes can be used not only for the determination of substrates but also for the analysis of enzyme inhibitors. In this type of sensors the response of the detectable species will decrease in the presence of the analyte. The inhibitor may affect the vmax or KM values. Competitive inhibitors, which bind to the same active site than the substrate, will increase the KM value, reflected by a change on the slope of the Lineweaver-Burke plot but will not change vmax. Non-competitive inhibitors, i.e. those that bind to another site of the protein, do not affect KM but produce a decrease in vmax. For instance, the acetylcholinesterase enzyme is inhibited by carbamate and organophosphate pesticides and has been widely used for the development of optical fiber sensors for these compounds based on different chemical transduction schemes (hydrolysis of a colored substrate, pH changes). 

Urine catecholamines may also serve as biomarkers of disulfoton exposure. No human data are available to support this, but limited animal data provide some evidence of this. Disulfoton exposure caused a 173% and 313% increase in urinary noradrenaline and adrenaline levels in female rats, respectively, within 72 hours of exposure (Brzezinski 1969). The major metabolite of catecholamine metabolism, HMMA, was also detected in the urine from rats given acute doses of disulfoton (Wysocka-Paruszewska 1971). Because organophosphates other than disulfoton can cause an accumulation of acetylcholine at nerve synapses, these chemical compounds may also cause a release of catecholamines from the adrenals and the nervous system. In addition, increased blood and urine catecholamines can be associated with overstimulation of the adrenal medulla and/or the sympathetic neurons by excitement/stress or sympathomimetic drugs, and other chemical compounds such as reserpine, carbon tetrachloride, carbon disulfide, DDT, and monoamine oxidase inhibitors (MAO) inhibitors (Brzezinski 1969). For these reasons, a change in catecholamine levels is not a specific indicator of disulfoton exposure. 

The application of fluorogenic labeling to the determination of some organophosphate insecticides has been attempted [178,179]. Fenthion (0,0-dimethyl 0-[(4-metiiylthio)-m-tolyl] phosphorothioate), Ruelene (0-2-chloro-4-ferf.-butylphenyl O-methyl methyl-phosphoramidate), GC 6506 [dimethyl p-(methylthio)phenyl phosphate] and several other compounds which yield phenols on hydrolysis have been examined. The limits of detection for some of these labeled derivatives have been reported to be in the low nanogram range. The organophosphate Proban [0,0-dimethyl 0-(p-sulphamoylphenyl) phosphorothioate] has been determined directly without hydrolysis by dansylation of the free amino group of the molecule [180]. The derivative exhibited blue fluorescence, as compared to yellow for phenol and alkylamine dansyl derivatives. 

The detection of organophosphate and other pesticides based on the inhibition of the enzyme acetylcholinesterase by these compounds has received considerable attention primarily due to high specificity and sensitivity [1,7-16]. Cholinesterases, such as acetylcholinesterase,... 

Figure 8.29 Separation and detection of organophosphate nerve agent compounds (a) 1.0 x 10-5M paraoxon, (b) 1.0 x 10-5M methyl parathion, (c) 2.0 x 10-5M fenitrothion, and (d) 4.0 x 10-5 M ethyl parathion [24].

Other materials were also employed to construct electrodes for amperometric detection. For instance, a boron-doped diamond (BOD) electrode was used for amperometric detection of nitroaromatic explosives, organophosphate nerve agents, and phenols. The BOD electrode offers enhanced sensitivity, lower noise, negligible adsorption of organic compounds, and low sensitivity to oxygen [760], In addition, a copper particle-modified carbon composite electrode was used for amperometric detection of glucose in a PDMS chip [761]. 

The non-polar chlorinated hydrocarbon pesticides are routinely quantified using gas chromatography (GC) and electron capture(EC) detection. Alternate detectors include electrolytic conductivity and microcoulometric systems. Organophosphate pesticides which are amenable to GC are responsive to either the flame photometric detector (FPD) or the alkali flame detector (AFD). Sulfur containing compounds respond in the electrolytic conductivity or flame photometric detectors. Nitrogen containing pesticides or metabolites are generally detected with alkali flame or electrolytic conductivity detectors. 

In case of the qualitative test applied for the qualitative analysis of organophosphate and/or carbamate pesticides, the inhibition of the biosensor was observed both in RM08 and RM10, thus detected the presence of the organophosphate and/or carbamate pesticides. The applied test is simple, easy-to-use and rapid, thus suitable for field measurement. However, provides information only about the presence of the representatives of the organophosphate and carbamate groups and does not allow the identification of the compounds that are present. 

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