Pesticides determining

Many pesticides are neurotoxicants poisoning the nervous system. A number of pesticides are acetyl cholinesterase inhibitors (Serat and Mengle 1973). Generally, pesticides determination has been performed by GC since the 1960 s (Morrison and Durham 1971 Fournier et al. 1978). There are no reference materials for pesticides in urine or serum, although as with PAHs there are a number biological matrices certified for the content of various pesticides available for environmental food and agriculture analysis and which may have some application in clinical chemistry. 

The concept of SPME was first introduced by Belardi and Pawliszyn in 1989. A fiber (usually fused silica) which has been coated on the outside with a suitable polymer sorbent (e.g., polydimethylsiloxane) is dipped into the headspace above the sample or directly into the liquid sample. The pesticides are partitioned from the sample into the sorbent and an equilibrium between the gas or liquid and the sorbent is established. The analytes are thermally desorbed in a GC injector or liquid desorbed in a liquid chromatography (LC) injector. The autosampler has to be specially modified for SPME but otherwise the technique is simple to use, rapid, inexpensive and solvent free. Optimization of the procedure will involve the correct choice of phase, extraction time, ionic strength of the extraction step, temperature and the time and temperature of the desorption step. According to the chemical characteristics of the pesticides determined, the extraction efficiency is often influenced by the sample matrix and pH. 

In AChE-based biosensors acetylthiocholine is commonly used as a substrate. The thiocholine produced during the catalytic reaction can be monitored using spectromet-ric, amperometric [44] (Fig. 2.2) or potentiometric methods. The enzyme activity is indirectly proportional to the pesticide concentration. La Rosa et al. [45] used 4-ami-nophenyl acetate as the enzyme substrate for a cholinesterase sensor for pesticide determination. This system allowed the determination of esterase activities via oxidation of the enzymatic product 4-aminophenol rather than the typical thiocholine. Sulfonylureas are reversible inhibitors of acetolactate synthase (ALS). By taking advantage of this inhibition mechanism ALS has been entrapped in photo cured polymer of polyvinyl alcohol bearing styrylpyridinium groups (PVA-SbQ) to prepare an amperometric biosensor for... 

M.A. Sirvent, A. Merkoci, and S. Alegret, Pesticide determination in tap water and juice samples using disposable amperometric biosensors made using thick-film technology. Anal. Chim. Acta 442, 35-44 (2001). 

E. Mallat, D. Barcel6, C. Barzen, G. Gauglitz, and R. Abuknesha, Immunosensors for pesticide determination in natural waters. Trac-Trends Anal. Chem. 20, 124-132 (2001). 

A particular interest for clinical applications was a possibility for detection of dopamine by its oxidation on nickel [19], cobalt [65], and osmium [66] hexacyanofer-ates. Except for oxidation of dopamine, cobalt and osmium hexacyanoferrates were active in oxidation of epinephrine and norepinephrine. For clinical analysis it is also important to carry out the detection of morphine on cobalt [67] and ferric [68] hexacyanoferrates, as well as the detection of oxidizable amino acids (cystein, methionine) by manganous [69] and ruthenium [70] hexacyanoferrate-modified electrodes. In general, oxidation of thiols was first shown for Prussian blue [71] and nickel hexacyanoferrate [72], This approach has been used for the detection of thiols in rat striatum microdialysate [73], Alternatively, the detection of thiocholine with Prussian blue was employed for pesticide determination in acetylcholine-esterase test [74],... 

Effects assessment, by, as in the case of risk assessment for chemicals and pesticides, determining a set of marker organisms (including algae, zebrafish, insect larvae, benthic worm, water flea, etc.) that represent ecosystem components and food networks and are used to indicate acute and chronic effects. This step is also used to define the predicted no-effect concentrations (PNECs). 

Miles CJ, Zhou M. 1990. Multiresidue pesticide determinations with a simple photoconductivity HPLC detector. J Agric Food Chem 38 986-989. 

A bibliographic search has shown that the majority of the HPLC techniques for determining OPPs and OCPs have been applied to the determination of residues in surface, ground- and drinking water. Table 5 lists pesticides determined, extraction and cleanup methods used, HPLC conditions, contaminated matrix and analyte detection limits taken from the literature for water, animal tissues, milk, fruit and vegetables, and cereals. The majority of the studies were done on spiked samples, and in the best of cases there were few real samples analyzed. 

A Navas, A Garcia, F Garcia. Liquid and gas chromatographic multi-residue pesticide determination in animal tissues. Pestic Sci 49 56-64, 1997. 

Immunotechniques have recently been developed to detect food contaminants, e.g., toxins, growth hormone, antibiotics, pesticides, and herbicides. Penicillin (62) in milk, aflatoxins and mycotoxins (63, 64, 65) in milk, cheeses, yogurt, corn have been detected by immunosensors. Characteristics of protein and receptors in or on the cell surface were used in detecting pathogens such as Listeria and Salmonella by immunosensors (11, 66). The principle of immunosensors has also been applied in pesticide determinations (67, 68). 

A.N. Ivanov, G.A. Evtugyn, R.E. Gyurcsanyi, K. Toth and H.C. Budnikov, Comparative investigation of electrochemical cholinesterase biosensors for pesticide determination, Anal. Chim. Acta, 404 (2000) 55-65. 

The inhibition and the subsequent signal detection were performed in two different solutions. First the pesticide solution was added and then after 10 min (incubation time) the sensor was moved into a new buffer solution where the substrate (5mmoll 1 acetylthiocholine) was injected and the signal measured. This procedure is particularly suitable when a complex matrix, which could pose problems for the direct measurement of thiocholine oxidation, is used. The analytical characteristics of pesticide determination in standard solutions were then evaluated. Detection limits, defined in this work as the concentrations giving an inhibition of 20%, were 30 and 10 ppb for aldicarb and paraoxon, respectively. By increasing the incubation time up to 30 min, an increase in the degree of inhibition could be observed and lower detection limits both for Aldicarb (5 ppb) and Paraoxon (3 ppb) were achieved. 

ChE/PB sensors showed a high reproducibility resulting in a relative standard deviation for the pesticide determination of 7% (n — 5). The results were obtained with single-use ChE/PB sensors. 

The presence of a pesticide determined on one column must be confirmed on an alternate column. Also, certain pesticides coeluting on one column can be separated by using another column. For example, 4,4 -DDD and Endosulfan-II coeluting on SP-2250/SP-2401 can be effectively separated on the OV-1 packed column. Conversely, 4,4-DDE and Dieldrin coeluting on OV-1 are better separated on SP-2250/SP-2401 column. Mary chlorinated pesticides may coelute even on... 

Analytical methodology for pesticide determinations has greatly advanced k during the past 30 years. The emphasis during the first 20 years was placed on increased sensitivity of detection. That these efforts were successful is attested by achieving sensitivity both quantitatively and qualitatively in the femtogram range (10 1S g). 

Fernandes, V.C., Subramanian, V., Mateus, N., Domingues, V.F., Deleme-Matos, C. The development and optimization of a modified single-drop microextraction method for organo-chlorine pesticides determination by gas chromatography-tandem mass spectrometry. Microchim. Acta 178, 195-202 (2012)... 

As outlined below, many factors combine to define the exposure scenario. In turn, the scenario combined with the toxicity of the pesticide determines the level of protection that should be used. 

Recoveries of pesticides, determined operating MS analysis in selected ion monitoring (SIM) mode, are between 85% and 101% (mostly >95%), repeatability is typically <5%. Extracts are analyzed by GC-MS using the analytical conditions reported in Table 6.6. Pesticides with their retention time and ions used for quantification in SIM mode are reported in Table 6.7. 

Cabras, P., Tuberoso, C., Melis, M. and Martini, M.G. (1992) Multiresidue method for pesticide determination in wine by high-performance liquid chromatography, T. Agric. Food Chem., 40(5), 817-819. 

Fernandez, M. J., Garcia, C., Garcia-Villanova, R. J., and Gomez, J. A., Evaluation of liquid-solid extraction with a new sorbent and LEE for multiresidue pesticides. Determination in raw and finished drinking waters, J. Agric. Food Chem., 44, 1790-1795, 1996. 

Specification of the GC Detectors Used for Organophosphorus Pesticides Determination ... 

LC-MS Conditions for Organophosphorus Pesticides Determination Ionization Modes, m/z Used for Quantification and Detection Limits ... 

Precursor Ion m/z and Product Ion m/z Monitored in MRM Mode for Some Organophosphorus Pesticides Determined by LC-MS/MS ... 

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