Pesticide confirmation

The most widely regarded approach to accomplish the determination of as many pesticides as possible in as few steps as possible is to use MS detection. MS is considered a universally selective detection method because MS detects all compounds independently of elemental composition and further separates the signal into mass spectral scans to provide a high degree of selectivity. Unlike GC with selective detectors, or even atomic emission detection (AED), GC/MS may provide acceptable confirmation of the identity of analytes without the need for further information. This reduces the need to re-inject a sample into a separate GC system (usually GC/MS) for pesticide confirmation. Through the use of selected ion monitoring (SIM), efficient ion-trap or quadrupole devices, and/or tandem mass spectrometry (MS/MS), modern GC/MS instruments provide LODs similar to or lower than those of selective detectors, depending on the analytes, methods, and detectors. 

Online Readino Development of green pesticides Confirm, Mack 2 and... 

Sample Cleanup. The recoveries from a quick cleanup method for waste solvents based on sample filtration through a Elorisd and sodium sulfate column are given in Table 2 (40). This method offers an alternative for analysts who need to confirm the presence or absence of pesticides or PCBs. 

In 1974, the Harmonized Monitoring Programme was set up by the Department of the Environment (DoE). The objective was to provide a network of sites at the lower end of catchments, where water quality data could be collected and analysed in a nationally consistent manner, allowing the loads of materials carried through river catchments into estuaries to be estimated and long-term trends in river quality to be assessed. The complete list of substances to be monitored is diverse and specifies about 115 substances. The pesticides aldrin, dieldrin, y-HCH, heptachlor, p,p -DDT and p,p -DDE are included. Figures 1 and 2 show the downward trend of y-HCH and dieldrin over the past 20 years at the Harmonized Monitoring Sites. This confirms that reductions in environmental concentrations have been achieved, particularly over the past 10 years. 

Once pesticides were identified, monitoring was undertaken by the NRA, where possible, to confirm the usefulness of the model predictions. The most important prediction from the model was that the herbicide bentazone would reach surface waters. Subsequent analysis by the NRA confirmed the detection of bentazone at concentrations above 0.1 /tg D Consequently, the NRA informed... 

Figure 13.13 On-line trace eniicliment-RPLC-diode-aiTay detection (DAD) cliromatogram (at 230 nm) obtained from 200 ml of tap water spiked with various pesticides at levels of 1 p.g L. Reprinted from Chromatographia, 43, C. Aguilar et al., Deteimination of pesticides by on-line ti ace emicliment-reversed-phase liquid clrromatography-diode-aiTay detection and confirmation by paiticle-beam mass specti ometi y , pp. 592-598, 1996, with permission from Vieweg Publisliing.

C. Aguilar, I. Feirer, R Bonnll, R. M. Marce and D. Barcelo, Monitoring of pesticides in river water based on samples previously stored in polymeric cartridges followed by on-line solid-phase extraction-liquid cliromatography-diode array detection and confirmation by atmospheric pressure chemical ionization mass spectrometry . Anal. Chim. Acta 386 237-248 (1999). 

C. Aguilar, R Bomtll and R. M. Marce, Determination of pesticides by on-line trace enrichment-reversed-phase liquid cliromatogr aphy-diode-array detection and confirmation by particle-beam mass spectrometry , Chromatographia 43 592-598 (1996). 

However, the American consumer now seems ready to accept some reduction in cosmetic standards, provided pesticide use is diminished (47). Their concern about pesticide use is confirmed by the growing popularity of organic food stores and supermarkets that guarantee pesticide-free produce (48). Also, the "Big Green" initiative in California, although it didn t pass, signals that consumers are alarmed about pesticide use and are willing to take political action to make their views known. 

Ambrus A, Visi W, Zakar F, et al. 1981. General method for determination of pesticide residues in samples of plant origin, soil, and water. III. Gas chromatographic analysis and confirmation. J Assoc Off Anal Chem 64 749-768. 

Lee H-B, Weng L-D, Chau AS. 1984. Confirmation of pesticide residue identity XI. Organophosphorus pesticides. J AOAC 67 553-556. 

Chau ASY. 1972. Confirmation of pesticide residue identity V. Alternative procedure for derivative formation in solid matrix for the confirmation of alpha- and beta endosulfan by gas chromatography. J Assoc Off Anal Chem 55 1228-1231. 

Because of the special regulatory position occupied by foods and beverages, a great deal of attention has been given to development and application of analytical procedures for them. Improved procedures have resulted in quantitation and confirmation levels in the range of 1 to 10 ppb with sample amounts of 10 to 250 g. Detection limits for foods are in the 0.1 to 1 ppb range. Detection limits of 0.1 to 1 ppm appear adequate for pesticide formulations (1, > while sensitivity of 0.01,... 

Mass spectrometry (MS) has proven to be far superior to other forms of detection for the determination and confirmation of pesticide residues in food, because its... 

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. 

As with GC/MS, LC/MS offers the possibility of unequivocal confirmation of analyte identity and accurate quantiation. Similarly, both quadrupole and ion-trap instruments are commercially available. However, the responses of different analytes are extremely dependent on the type of interface used to remove the mobile phase and to introduce the target analytes into the mass spectrometer. For pesticide residue analyses, the most popular interfaces are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). Both negative and positive ionization can be used as applicable to produce characteristically abundant ions. 

The development of a robust analytical method is a complex issue. The residue analyst has available a vast array of techniques to assist in this task, but there are a number of basic rules that should be followed to produce a reliable method. The intention of this article is to provide the analyst with ideas from which a method can be constructed by considering each major component of the analytical method (sample preparation, extraction, sample cleanup, and the determinative step), and to suggest modern techniques that can be used to develop an effective and efficient overall approach. The latter portion emphasizes mass spectrometry (MS) since the current trend for pesticide residue methods is leading to MS becoming the method of choice for simultaneous quantitation and confirmation. This article also serves to update previous publications on similar topics by the authors. ... 

The combination of an element-selective detector and MS can provide excellent information for determining the presence of an analyte or, just as important, eliminating the chance that a pesticide is present. The added selectivity gained in the use of tandem MS (MS") can also weigh heavily in confirmation of pesticide identity despite the possible lack of three ions of defined ratios. 

Most problems linked to the environmental consequences of wide pesticide use are due to the fact that almost all pesticides are xenobiotic (from the Greek xenos - foreign, and bios - life), i.e. they are chemical substances that are foreign to the natural environment. Materials from the USSR confirm all the concerns about pesticides dangerous effects on the natural environment. 

Generalizing the data we have already, we can confirm that all pesticides negatively affect the reproduction of at least some animals. 

Besides alkylphosphates, OP metabolism gives rise to the production of other metabolites that can be used as exposure markers (Table 4). Unchanged OP compounds in blood or urine can also be measured to confirm exposure (Table 4), but this method is of limited use for routine biological monitoring of occupational exposure, as OP compounds are rapidly excreted in urine. Moreover, most OP pesticides are unstable, and, with a few exceptions, they are not detectable in biological specimens after a few hours. So far, the measurement of unchanged compounds in biological fluids has been performed primarily for research purposes and has limited practical applicability. 

There is a growing need to better characterize the health risk related to occupational and environmental exposure to pesticides. Risk characterization is a basic step in the assessment and management of the health risks related to chemicals (Tordoir and Maroni, 1994). Evaluation of exposure, which may be performed through environmental and biological monitoring, is a fundamental component of risk assessment. Biomarkers are useful tools that may be used in risk assessment to confirm exposure or to quantify it by estimating the internal dose. Besides their use in risk assessment, biomarkers also represent a fundamental tool to improve the effectiveness of medical and epidemiological surveillance. 

Due to the low volatility of cyromazine and the use of water-soluble bags for packaging the Trigard formulation, the main routes of exposure were expected to be from direct contact with the product or spray mixture on contaminated surfaces. Previous experience with pesticides worker exposure studies indicated that exposure from vapors or spray mist would be a minor factor. This can easily be confirmed by the PHED or similar published sources however, the extent of exposure from inhaling the product as dust is less well known. This route of exposure was also assumed to be minor, particularly with the use of water-soluble bag packaging. Given the low mammalian toxicity of cyromazine, the operators did not wear respiratory protection. 

Half-life estimates of approximately 28 days for thiophanate-methyl indicate a very slow decay compared to methiocarb with an estimate of half-life of about 11 days. The application of a model based on a first-order decay process resulted in fairly high R2 and significant fit. The results suggest that both pesticides are relatively stable compared to other compounds under similar environmental conditions (Brouwer et al., 1994). With respect to the objectives of the study and the proposed model, it can be stated that the results confirm the assumption of a linear relationship between application rate (for both application techniques) and the increase of dislodgeable foliar residue. This relationship holds for modeling purposes. The contribution of the crop density or total crop surface area to the process of interception cannot be quantified with the results of the present study. Because the interception factor ranges from about 0.35 to 0.9 (Willis and McDowell, 1987), the... 

These in vivo and in vitro human metabolism studies indicate that pyrethroids undergo rapid metabolism and elimination as observed in rats, and qualitative metabolic profiles (e.g., kinds of metabolites) of pyrethroids are assumed to be almost the same between humans and rats, suggesting that a large database of animal metabolism of pyrethroids could provide useful information for the evaluation of behavior of pyrethroids in humans. Nowadays, human pesticide dosing studies for regulatory propose are severely restricted in the US, and thus detailed comparison of in vitro metabolism (e.g., metabolic rate constants of pathways on a step-by-step basis) using human and animal tissues could be an appropriate method to confirm the similarity or differences in metabolism between humans and animals. 

Although the results presented only reflect agricultural practices of a single year, findings confirm that herbicides are the most widely used type of pesticide, as weeds are the major constraint that limit yield in many crops in conventional crop cultivation systems. According to CropLife (2004), herbicides represent around 50% of all crop protection chemicals used throughout the world, compared with insecticides and fungicides that each account for around 17%. 

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