Pesticides qualitative analysis

However, for NOM investigation, most interest in UV-vis absorption is related to qualitative analysis. Relative intensity and change of position of bands indicate structural differences as chain breakdown, formation or cleavage of inter- and intramolecular bounds, and interactions of OM with xenobiotics such as pesticides. The necessity to dissolve the analyte makes the analysis of the whole SOM difficult. Thus, in general, HS dissolved in water are the usual way to obtain an UV-vis spectrum. 

The objective of an analytical measurement can be qualitative or quantitative. For example, the presence of pesticide in fish is a topic of concern. The questions may be Are there pesticides in fish If so, which ones An analysis designed to address these questions is a qualitative analysis, where the analyst screens for the presence of certain pesticides. The next obvious question is How much pesticide is there This type of analysis, quantitative analysis, not only addresses the presence of the pesticide, but also its concentration. The other important category is semiqualitative analysis. Here... 

ChE-ChOx bienzyme-modified biosensors have been widely used mainly for detecting OP pesticides, which are summarized in Table 55.1. AChE and BChE are often used as ChE enzyme. This type of ChE-ChOx sensor can be used conveniently for detecting OP compounds, and detection time for qualitative analysis is reasonably fast. For quantitative determination of OP compounds, however, operation of the sensor is somewhat time consuming because multiple steps (a measurement of response to acetylcholine and inhibition) are required. 

Most applications of DLI LC-MS deal with qualitative analysis, where in most cases only molecular-mass information is obtained. DLI LC-MS found extensive apphcation in the analysis of pesticides and related compounds [35], in the quahtative and quantitative determination of corticosteroids and metabolites in equine urine [36]. Highly labile compounds such as vitamin B12 (molecular weight 1354) and erythromycin A (molecular weight 733) were analysed by DLI negative-ion Cl LC-MS [33]. As an example, the negative-ion Cl spectram of 92 ng vitamin B12 is shown in Figure 4.7. 

Qualitative analysis of chiral compounds, including drugs, pesticides, carbohydrates, amino acids, liquid crystals, and other biochemicals Determination of enantiomeric purity of chiral compounds... 

Qualitative analysis for pesticides and PAHs - ecotoxicity tests... 

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. 

The enforcement of this legislation has led to an increasing need from analysts to develop reliable, effective methods for qualitative and quantitative pesticide residue analysis in environmental and food matrices. EEC Directive 80/778, which is concerned with the quality of water designated for human consumption, has established the maximum admissible concentration of each individual pesticide at 0.1 /rg/l and the total amount of pesticides at 0.5 /rg/1. Other countries (e.g., U.S.A. and Australia) have established concentration limits based on the values recommended by WHO. Such values are based on the acceptable daily intake (ADI), which is calculated as the 20% ADI for a person of 70 kg drinking 2 1 of water per day. "... 

Commercial Immunoassay Kits. Most commercially available immunoassay kits have been developed for determination of pesticides in water. At a minimum, appropriate residue extraction procedures must be developed before these kits can be applied to pesticide residue analysis of foods. Encouraging results have been obtained in preliminary FDA evaluations of several kits (12). For example, in studies of a kit for detection of triazine herbicides, a typical residue extraction solvent (acetonitrile) was used and then diluted with water to levels tolerated by the immunoassay. Visual comparison of color developed for extract, standard, and reagent blank was made for qualitative analysis. Spectrophotometric readings of the color were made for quantitative analysis. 

The smallest detectable signal cannot be less than double the height of the largest noise peak, e.g. 5 ng of dithianone (a pesticide) in Fig. 6.2. If the amount injected is even less, then the signal ceases to be distinguishable from noise. For qualitative analysis the signal-to-noise ratio should not be lower than 3-5 for quantitative analysis it must be higher than 10. 

PA Tanner, K-H Leung. Spectral interpretation and qualitative analysis of organophosphorus pesticides using FT-Raman and FT infrared spectroscopy. Appl Spectrosc 50 565-571, 1996. 

Analysis of On-Site Wastewaters for Pesticides by Thin-Layer Chromatography. A field method to identify qualitatively and semi-quantitatively the pesticide constituents of a pesticide-laden wastewater was developed. The field method was developed using thin-layer chromatography (TLC). TLC gives a presumptive test for the presence of specific pesticides and within 30 minutes an estimate of their concentrations. TLC may also reveal the presence of unknown substances. The field application of thin-layer chromatography requires a skilled chemist, but no expensive equipment. The following protocol describes the on-site use of TLC. 

Figure 3. Flow chart showing the qualitative and quantitative analysis of a complex pesticide waste (2).

They considered it important to distinguish between simple and complex mixtures. According to Feron et al. (1998) a simple mixture consists of a relatively small number of chemicals (e.g., 10 or less) and the composition of the mixture is known, both qualitatively and quantitatively. An example would be a cocktail of pesticide residues in food. A complex mixture comprises tens, hundreds, or thousands of chemicals, and the qualitative and quantitative composition is not ftiUy known. They also emphasized to distinguish between whole-mixture analysis (top-down approach) and component-interaction analysis (bottom-up approach), the latter requiring an understanding of the basic concepts of combined action of chemicals. 

In food analysis, sensitivity is not the only requirement for analytical method development. Besides confirmation of the identity of pesticides, the identification of nontarget analytes is also important. One powerful tool is LC/MS, especially when it is combined with appropiate sample-treatment procedures it allows one to obtain detection limits adequate for trace-level analysis. Liquid chromatography-MS has demonstrated that it is an effective way to obtain both qualitative and quantitative information. 

Enzyme immunoassay kits are now available for qualitative field testing or for laboratory screening and semiquantitative analysis of pesticides, herbicides, polychlorinated biphenyls (PCBs), mononuclear and polynuclear aromatic hydrocarbons, pentachlorophenol, nitroorganics, and many other compounds in aqueous and soil samples. Certain analytes may be quantitatively determined as well, with a degree of accuracy comparable to gas chromatography or high performance liquid chromatography determination. The method is rapid and inexpensive. 

The confirmation of pesticides by GC/MS should be more reliable than that on the GC-ECD using an alternate column. Presence of stray interference peaks, even after sample cleanup, and the retention time shift and coelution problem, often necessitate the use of GC/MS in compounds identification If a quantitative estimation is to be performed, select the primary ion or one of the major characteristic ions of the compounds and compare the area response of this ion to that in the calibration standard. Quantitation, however, is generally done from the GC-ECD analysis, because ECD exhibits a much greater sensitivity than the mass selective detector (MSD). For example, while ECD is sensitive to 0.01 ng dieldrin, the lowest MSD detection for the same compound is in the range of 1 ng. The primary and secondary characteristic ions for qualitative identification and quantitation are presented in Table 2.20.3. The data presented are obtained under MS conditions utilizing 70 V (nominal) electron energy under electron impact ionization mode. 

Several qualitative and quantitative immunochemical methods and their application to the analysis of environmental samples have been described for OP insecticides, a family that includes widely used pesticides such as azinphos-ethyl/methyl, dichlorvos, fenitrothion or fenthion, malathion, mevinphos, and parathion. Mercader and Montoya202 produced monoclonal antibodies against azinphos-methyl and developed an ELISA that was used for the analysis of water samples from different sources, reaching detectability levels near 0.05 pg I. Watanabe et al.203 reported the production of polyclonal antibodies and ELISA procedures to analyze fenitrothion in river, tap, and mineral water (LOD = 0.3 pg L ). Banks et al.204 produced polyclonal antibodies against dichlorvos, an organophosphate insecticide used for stored grain, which also cross-reacts with fenitrothion. Nishi et al.205 reported the first immunoassay for malathion. Residues of this insecticide have... 

In conclusion, it is obvious that chemical derivatization continues and will continue to play an important role in both qualitative and quantitative analysis of pesticides, their residues and metabolites. One of the major advantages being that derivatization gives an improvement in selectivity as a result of the formation of a characteristic derivative which responds selectively to certain GC and HPLC detectors. 

Methods of Analysis of Pesticides. The extracted residue obtained after isolation from tissues and other biological materials is subjected to qualitative and quantitative determination of the pesticides. Sometimes, the amount of material available is so small that the colorimetric and other allied methods cannot be successfully applied as some of the residue is likely to be lost during the purification technique. Furthermore, these purification techniques required for spectrophotometry, colorimetry, and other sophisticated instrumental methods are appreciably time consuming. Therefore, other techniques were sought for the quantitative determination of pesticides. Thin layer chromatographic (TLC) techniques were found to be most suitable for toxicological analysis of pesticides. Randerath(16j stated that... 

The methods used to correlate suspensibility may be used with other response variables — such as biological activity, stability, or yield value — that are important in the development of pesticides. Also, formulations of greater complexity, which have more components, can be studied with the same correlational techniques. There are, however, many important response variables that are qualitative or semiquantitative and are not usually estimated with the precision necessary for reliable regression analysis. These include, freeze-thaw stability, bloom, compatibility, and... 

It is one of the aims of the lUPAC project to qualitatively and quantitatively assess the impact of altered pesticide use on GM crops. Furthermore, otho impacts will also be taken into account, which may include weed eeology and soil conservation. Finally a risk-benefit analysis of these impacts will be made by evaluating the various outcomes of our research, which may provide a tool for further polieies in the area of GM crop cultivation and pest management. This is an important endeavour given the public concerns regarding large scale cultivation of GM crops and its environmental consequences. 

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