Organophosphates detection limits

Organophosphate ester components of hydraulic fluids such as triphenyl phosphate, nonylphenyl diphenyl phosphate, and cumylphenyl phosphate also have been detected in fish concentrations of 0.1-0.9 pg/g of fish tissue were detected principally near manufacturing facilities, while fish caught in other areas generally had concentrations below the detection limit (0.1 pg/g) (Mayer et al. 1981). In a market basket survey, tributyl phosphate was found to be present in 2% of the foods analyzed between April 1982 and April 1984 (Gunderson 1988). Intakes of tributylphosphate were estimated to be a maximum of 38.9 ng/kg body weight/day for 6- to 11-month-old children. 

Water samples are acidified and extracted with solvent (Kawamura and Kaplan 1983 Muir et al. 1981). Clean-up steps may be used (Kawamura and Kaplan 1983). Methylene chloride is often used as the extracting solvent, and it may interfere with the nitrogen-phosphorus detector. In this case, a solvent-exchange step is used (Muir et al. 1981). Analysis by GC/NPD or GC/MS provides specificity (Kawamura and Kaplan 1983 Muir et al. 1981). Accuracy is acceptable (>80%), but precision has not been reported. Detection limits were not reported, but are estimated to be 0.05-0.1 pg/L (Muir et al. 1981). Detection limits at the low ppt level (ng/L) were achieved by concentrating organophosphate esters on XAD-2 resin. The analytes were solvent extracted from the resin and analyzed by GC/NPD and GC/MS. Recovery was acceptable (>70%) and precision was good (<10% RSD) (LeBel et al. 1981). 

In the United States, methods for several pesticides at occupational levels in air are given in the National Institute for Occupational Safety and Health (NIOSH) Manual of Analytical Methods (Eller, 1994). The NIOSH methods for organochlo-rines and organophosphates utilize small traps with a particle filter backed up by two Amberlite XAD-2 resin beds. They are designed to be used with personal sampling pumps operating at flow rates of 0.2 to 1 L/min for maximum sample volumes of 60 to 240 L. Detection limits are in the 5 ng/m to 600 ng/m range. 

The flame photometric detector (FPD) is selective to sulphur- or phosphorus-containing compounds and it has been used in the determination of organophosphorus FRs. In FPD, the emitter for phosphorus compounds in the flame is excited HPO (Xj ax = doublet 510 to 526 nm) and detection requires a suitable interference filter for isolation of the emission band. For organophosphorus FRs, a phosphorus filter at 526 nm has been used in the detection. The detection limits for the organophosphates have been on the ng level. 

A short review of methods for the analysis of biocides in household dust is given in Table 3.5-2. Most methods use either toluene or ethyl acetate for the extraction of organic compounds. In some cases, especially for methods having low detection limits, an additional clean-up with Florisil or silica gel is added. Methods of quantifying the substances of interest in the (cleaned) extract are either GC-ECD or GC-MS. All procedures are rather similar for carbamates, organochlorine compounds, organophosphates and pyre-throids. For the analysis of some phenols, e.g. pentachlorophenol, a derivatization step (alkylation, acetylation) is necessary. 

The active site of organophosphorus hydrolase (OPH) contains two metal atoms (zinc in the wild-type enzyme) and catalyzes hydrolysis of numerous organophos-phate compounds including pesticides as well as chemical warfare agents such as sarin and soman. Rates of OPH catalyzed hydrolysis of organophosphates exceed those of chemical hydrolysis by NaOH at 4°C by factors of 40 to 2450 [41-43]. The enzyme has been described for use in sensor systems with exceptional detection limits reported for response times on the order of 10 seconds [44-48]. However, the presence of OP/CWA is detected by the inhibition of enzymatic rate determined by comparing rate measnrements in the presence and absence of the analyte. 

CoPc modified carbon paste electrodes were reported by Chicharo et al. to show good catalytic activity towards the measurement of triazolic herbicides sueh as amitrole at low oxidation potential (+0.4 V, Table 7.1) in basic media, a detection limit of 0.04 jig mL was obtained using a injection system . A screen-printed carbon electrode which was impregnated with CoPc electrocatalyst, was employed in conjunction with acetylcholinesterase by Hartley and Hart for the reduction of organophosphate pesticides The detection limits were of the order of 10 and 10 ... 

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. 

Systematic investigation of pesticides in the Chesapeake Bay watershed began in the 1970 s in response to the observed decline in SAV and fish populations during that period. Investigations typically spanned a few years and tested for specific families of herbicides (e.g., dUoro-s-triazines and chloroacetanilides) and insecticides (e.g., organophosphates and chlorinated hydrocarbons) in various media. Detection limits and consistency in the methods of data collection improved with time. The data that are sununarized below consist of measurements of concentrations of atrazine in the iiqruts to surface waters at several locations throughout the Bay. We should stress that data are sparse spatial and temporal distributions have to be estimated and/or extrapolated from measurements in the top 0.5-1.0 m of the surface layer. 

Inhibition by organophosphates is a slow process and thus requires incubation to improve the detection limit. A very low pesticide concentration requires a longer incubation time to produce the same degree of inhilntion. For the same inhilntor concentration, the loss in enzymatic activity follows first order kinetics (Figure 4.25). 

The cholinesterase electrode was constructed on this basis for the total determination of organophosphates and carbamates [32]. This electrode is also sensitive to other toxic compounds with very low detection limits (paraquat (3 ppm) trichlorophenol (20 ppm) methylazinphos (150 ppb) lindane (15 ppm) and mercury (4 ppm)) [135]. This type of biosensor uses enzymatic inhibition and can be incorporated in an automated system for the quality control of water, and, notably, waste water [291]. 

No data were located regarding absorption in animals after inhalation exposure to organophosphate ester hydraulic fluids or specific organophosphate esters, except for the observation that parent material was not detected by gas chromatography in the blood or urine of male rats exposed to 5,120 mg/m3 of an aerosol of a cyclotriphosphazene (99.9%) hydraulic fluid for 4 hours, thereby suggesting that the extent of absorption was limited (Kinkead and Bashe 1987). Blood samples were collected at 0, 24, and 48 hours after exposure was terminated. Urine was collected for 24 hours after exposure. 

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. 

Method. A diagram of the apparatus is shown in Fig.4.29. Any suitable liquid chromatograph may be used. The AutoAnalyzer is modified such that the liquid sampler is fitted to the end of the chromatographic column. The proportioning pump is by-passed. The set-up of the AutoAnalyzer is the same as that for normal measurements of cholinesterase. The application of this technique to the determination of CGA 18809 in plum-leaf extract is shown in Fig.4.30. A comparison is made with UV analysis of the same extract. The limit of detection for CGA 18809 is c . 20 ng at a 3 1 signal to noise ratio. The relative inhibitions of several organophosphates and carbamates are compared in Table 4.9. Diazoxon may be detected in low picogram quantities. 

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. 

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