PESTICIDES IDENTIFICATION

Identification of the pesticides is based on retention time on at least two dissimilar glc columns. A nonpolar and a relatively polar packing are generaUy used, for example, OV-17 and a mixture of QE-1 and DC-200. 

Intensive application of pesticides and polymers in agriculture and industry cause the increase of number of toxic organic substances, which circulate in an environment, and constantly complicates their disclosure, identification and quantitative detection. 

Hazard identification, step one, means identification of new chemicals or other factors that may cause harmful health effects. Previously, novel hazards were usually observed in case studies or after accidents or other excessive exposures, usually in occupational environments. Today, thorough toxicity studies are required on all pesticides, food additives, and drugs. New chemicals also have to be studied for their potential toxic effects. Thus, earlier hazards were in most cases identified after they had caused harmful effects in humans. Today, most chemical products have been evaluated for their toxicity with experimental animals. Therefore, hazard identification has become a preventive procedure based on safety studies conducted before a chemical compound or product reaches the market, and before individuals are exposed to it. ... 

Figure 13.15 Chromatograms obtained by on-line ti ace enrichment of 50 ml of Ebro river water with and without the addition of different volumes of 10% Na2S03 solution for every 100 ml of sample (a) blank with the addition of 1000 p.1 of sulfite (b) spiked with 4 p.g 1 of the analytes and 1000 p.1 of sulfite (c) spiked with 4 p.g 1 of the analytes and 500 p.1 of sulfite (d) spiked with 4 p.g 1 of the analytes without sulfite. Peak identification is as follows 1, oxamyl 2, methomyl 3, phenol 4, 4-niti ophenol 5, 2,4-dinitrophenol 6, 2-chlorophenol 7, bentazone 8, simazine 9, MCPA 10, atrazine. Reprinted from Journal of Chromatography, A 803, N. Masque et ai, New chemically modified polymeric resin for solid-phase extraction of pesticides and phenolic compounds from water , pp. 147-155, copyright 1998, with permission from Elsevier Science.

Figure 13.19 Chromatograms obtained by on-line SPE-GC-MS(SIM) of (a) 10 ml of tap water spiked with pesticides at levels of 0.1 ng 1 (b) 10 ml of a sample of unspiked tap water. Peak identification foi (a) is as follows 1, molinate 2, a-HCH 3, dimethoate 4, simazine 5, ati azine 6, y-HCH 7, S-HCH 8, heptachloi 9, ametiyn 10, prometiyn 11, fen-itrothion 12, aldrin 13, malatliion 14, endo-heptachlor 15, a-endosulfan 16, teti achlor-vinphos 17, dieldrin. Reprinted from Journal of Chromatography, A 818, E. Pocumll et al., On-line coupling of solid-phase exti action to gas cliromatography with mass specti ometiic detection to determine pesticides in water , pp. 85-93, copyright 1998, with permission from Elsevier Science.

Figure 15.1 Separation of pesticides from butter by using LC-GC-ECD. Peak identification is as follows 1, HCB 2, lindane 5, aldrin 7, o,p -DDE 10, endrin 11, o,p -DDT 13, p,p -DDT peaks 3, 4, 6, 8, 9, 12, 14, 15 and 16 were not identified. Adapted from Journal of High Resolution Chromatography, 13, R. Barcarolo, Coupled EC-GC a new method for the on-line analysis of organchlorine pesticide residues in fat , pp. 465-469, 1990, with permission from Wiley-VCH.

Figure 15.13 Comprehensive two-dimensional GC chromatogram of a supercritical fluid exti act of spiked human semm. Peak identification is as follows 1, dicamha 2, tiifluralin 3, dicliloran 4, phorate 5, pentachlorophenol 6, atrazine 7, fonofos 8, diazinon 9, cWorothalonil 10, terhufos 11, alachlor 12, matalaxyl 13, malathion 14, metalochlor 15, DCPA 16, captan 17, folpet 18, heptadecanoic acid. Adapted imm Analytical Chemistry, 66, Z. Liu et al., Comprehensive two-dimensional gas chromatography for the fast separation and determination of pesticides exuacted from human senim , pp. 3086-3092, copyright 1994, with pemiission from the American Chemical Society.

Marutoiu C, Sarbu C, Vlassa M, et al. 1986. A new separation and identification method of some organophosphorus pesticide by means of temperature programming gradient thin-layer chromatography. Analysis 14 95-98. 

Marutoiu C, Vlassa M, Sarbu C, et al. 1987. Separation and identification of organophosphorus pesticides in water by HPTE. J High Resolution Chromatog Chromatog Comm 19 465-466. 

GC/ECD or a halogen-specific detector (HSD) (Method 8080) is the technique recommended by EPA s Office of Solid Waste and Emergency Response for determining a- and [3-endosulfan and endosulfan sulfate in water and waste water at low-ppb levels (EPA 1986a). At these low concentrations, identification of endosulfan residues can be hampered by the presence of a variety of other pesticides. Consequently, sample clean-up on a Florisil column is usually required prior to analysis (EPA 1986a). 

Hardy, A.R. (1990). Estimating exposure The identification of species at risk and routes of exposure. In L. Somerville and C.H. Walker (Eds.) Pesticide Effects on Terrestrial Wildlife, 81-98, London Taylor Francis. 

Validation of true extraction efficiency normally requires the identification and quantitation of field-applied radiolabeled analyte(s), including resulting metabolites and all other degradation products. The manufacturer of a new pesticide has to perform such experiments and is able to determine the extraction efficiency of aged residues. Without any identification of residue components the calculation of the ratio between extracted radioactivity and total radioactivity inside the sample before extraction gives a first impression of the extraction efficiency of solvents. At best, this ratio is nearly 1 (i.e., a traceability of about 100%) and no further information is required. Such an efficient extraction solvent may serve as a reference solvent for any comparison with other extraction procedures. 

Polar or thermally labile compounds - many of the more modern pesticides fall into one or other of these categories - are not amenable to GC and therefore LC becomes the separation technique of choice. HPLC columns may be linked to a diode-array detector (DAD) or fluorescence detector if the target analyte(s) contain chromophores or fluorophores. When using a DAD, identification of the analyte(s) is based on the relative retention time and absorption wavelengths. Similarly, with fluorescence detection, retention time and emission and absorption wavelengths are used for identification purposes. Both can be subject to interference caused by co-extractives present in the sample extract(s) and therefore unequivocal confirmation of identity is seldom possible. 

The principal limitation in the use of electrophoretic techniques is the lack of availability of suitable detection systems for quantitative analysis and unequivocal identification of pesticide analytes. Traditionally, either ultraviolet/visible (UVA IS) or fluorescence detection techniques have been used. However, as with chromatographic techniques, MS should be the detection system of choice. A brief comparison of the numbers of recent papers on the application of GC/MS and LC/MS with capillary elec-trophoresis/mass spectrometery (CE/MS) demonstrates that interfaces between CE... 

A polyethylene-coated (PEE) silica column was used with water-methanol eluents to achieve the separation and retention of 27 pesticides.40 The retention times of 33 commercial pesticides were determined on an octadecyl (ODS)-derivatized alumina column using water-methanol eluents and compared with retention properties on an ODS-silica column packing.41 More recently, RP-HPLC was used in combination with diode array detection for the identification and quantification of 77 pesticides (acidic, basic, and neutral) in groundwater samples.42... 

Vandecasteele, K., Gaus, I., Debreuck, W., and Walraevens, K., Identification and Quantification of 77 Pesticides in Groundwater Using Solid Phase Coupled to Liquid-Liquid Microextraction and Reversed-Phase Liquid Chromatography, Anal. Chem. 72, 3093, 2000. 

A dietary supplement may be safe when taken in the recommended doses but may become dangerous in higher doses. However, patients may develop side effects even when ingesting recommended doses. Adverse reactions may be due to allergic reactions, dietary supplements containing toxic substances, mis-identification of plant, mislabeling of plant, natural toxic substances such as pyrrolizidine alkaloids in comfrey, unnatural toxic substances such as heavy metals, or pesticides. 

At least 26 oxidative, 7 reductive, and 14 hydrolytic transformations of pesticides had been identified. Detailed identification and discussion of specific reactions can be found in the works of Alexander56 and Scow.57... 

As is the case with identifications based on protein molecular masses, it appears that the use of tryptic or other peptide masses as the basis for identification is extended with difficulty to mixtures of microorganisms. This reflects unpredictable suppression. Another limitation is redundancy of peptide masses across several microorganisms. For example, the most abundant proteins (SASPs), and thus the most abundant peptides, in spores of Bacillus anthracis and the closely related pesticide Bacillus thuringiensis have extensive sequence homology.25,82... 

MWNTs favored the detection of insecticide from 1.5 to 80 nM with a detection limit of InM at an inhibition of 10% (Fig. 2.7). Bucur et al. [58] employed two kinds of AChE, wild type Drosophila melanogaster and a mutant E69W, for the pesticide detection using flow injection analysis. Mutant AChE showed lower detection limit (1 X 10-7 M) than the wild type (1 X 10 6 M) for omethoate. An amperometric FIA biosensor was reported by immobilizing OPH on aminopropyl control pore glass beads [27], The amperometric response of the biosensor was linear up to 120 and 140 pM for paraoxon and methyl-parathion, respectively, with a detection limit of 20 nM (for both the pesticides). Neufeld et al. [59] reported a sensitive, rapid, small, and inexpensive amperometric microflow injection electrochemical biosensor for the identification and quantification of dimethyl 2,2 -dichlorovinyl phosphate (DDVP) on the spot. The electrochemical cell was made up of a screen-printed electrode covered with an enzymatic membrane and combined with a flow cell and computer-controlled potentiostat. Potassium hexacyanoferrate (III) was used as mediator to generate very sharp, rapid, and reproducible electric signals. Other reports on pesticide biosensors could be found in review [17],... 

Nolan BT, Dubus IG, Surdyk N, Fowler HJ, Burton A, Hollis JM, Reichenberger S, Jarvis NJ (2008) Identification of key climatic factors regulating the transport of pesticides in leaching and to tile drains. Pest Manage Sci. doi 10.1002/ps,1587... 

Kuehl, D.W., E.N. Leonard, K.J. Welch, and G.D. Veith. 1980. Identification of hazardous organic chemicals in fish from the Ashtabula River, Ohio, and Wabash River, Indiana. Jour. Assoc. Off. Anal. Chem. 63 1238-1244. Kunz, T.H., E.L.P. Anthony, and W.T. Rumage III. 1977. Mortality of little brown bats following multiple pesticide applications. Jour. Wildl. Manage. 41 476-483. 

Due to the predicted and previously detected low concentrations of pesticides in environmental samples (usually around the nanogram per liter level), a preconcentration step of the water samples is necessary prior to measurement. In this way, a preconcentration factor of several orders of magnitude (200-1,000-fold) is mandatory to reach the low detection limits necessary for the identification of pesticides, especially in complex wastewater samples. Also, the use of surrogate standards (e.g., triphenyl phosphate) added before the extraction step is a common practice in order to account for possible errors during the extraction process and for quantitative purposes. The commonly used extraction methods for polar compounds from water matrices involve isolation using liquid-liquid extraction (LLE) and solid-phase extraction (SPE), which are commented on below. Other methods such as semipermeable membrane devices (SPMD) are also mentioned. 

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