Pesticides chromatographic separation techniques

For analyzing water pollution it is necessary to know the area where the sample(s) were harvested. Among the primary water pollutants are pesticides, since they are slowly degraded and require dissemination. The chlorinated pesticides are lipophilic and are slowly accumulated in animals. The effect is due to metabolic system perturbation. Other water pollution sources are heavy metals, which are determined by the highly sensitive and selective analytical method ICP-AES.29 The sampling process, in this case, consists of chromatographic separation techniques for pesticide separation.30... 

Abstract This chapter gives an overview of strategies used in the identification and analysis of environmental transformation products of three important groups of synthetic chemicals pesticides, pharmaceuticals, and personal care products. The characteristics and features of modern mass spectrometric instrumentation coupled to liquid chromatographic separation techniques as well as complementary techniques are presented and examples of their application to the characterization of transformation products of synthetic chemicals are described. Analytical methodologies for the quantitative analysis of the intact parent compounds and their transformation products in the environment are compiled. 

The final stage of the residue analysis procedures involves the chromatographic separation and instrumental determination. Where chromatographic properties of some food residues are affected by sample matrix, calibration solutions should be prepared in sample matrix. The choice of instrument depends on the physicochemical properties of the analyte(s) and the sensitivity required. As the majority of residues are relatively volatile, GC has proved to be an excellent technique for pesticides and drug residues determination and is by far the most widely used. Thermal conductivity, flame ionization, and, in certain applications, electron capture and nitrogen phosphorus detectors (NPD) were popular in GC analysis. In current residue GC methods, the universality, selectivity, and specificity of the mass spectrometer (MS) in combination with electron-impact ionization (El) is by far preferred. 

Another disadvantage of enzyme techniques is that they lack the specificity to distinguish individual pesticides when present as a mixture. Most of the methods reported here (Table II) have been developed for single compounds, and thus where more than one pesticide is present, preliminary separation techniques are necessary. Both paper and thin layer chromatographic techniques do not have this disadvantage and... 

I urton, K. G. and Rein, J. 1990. Trends in techniques for the extraction of drugs and pesticides from biological specimens prior to chromatographic separation and detection. Anal. Chim. Acta, 236 99-114. 

Paper chromatography and other chromatographic techniques (see Chapter 21) depend on the principle of partitioning. It is also the basis for the separation technique of solvent extraction (see Chapter 20). We also need to know particular partition coefficients when developing pesticides and insecticides. Pesticides and insecticides need to be soluble in the fatty tissues of the animals that they are designed to kill, but much less soluble in water so that the chemicals are not simply washed away by rain. 

The need to develop and use chiral chromatographic techniques to resolve racemates in pesticide residues will be driven by new hazard and risk assessments undertaken using data from differential metabolism studies. The molecular structures of many pesticides incorporate chiral centers and, in some cases, the activity differs between enantiomers. Consequently, in recent years manufacturers have introduced resolved enantiomers to provide pesticides of higher activity per unit mass applied. For example, the fungicide metalaxyl is a racemic mix of R- and 5-enantiomers, both having the same mode of action but differing considerably in effectiveness. The -enantiomer is the most effective and is marketed as a separate product metalaxyl-M. In future, it will not be satisfactory to rely on hazard/risk assessments based on data from metabolism studies of racemic mixes. The metabolism studies will need to be undertaken on one, or more, of the resolved enantiomers. 

Determination of pesticide residues in fatty samples by GC requires the elimination of interfering compounds, mainly lipids, from the extracts before sample injection into the chromatographic system. Even small amounts of lipids can cause damage to the column and contaminate the detector. The effectiveness of HPLC techniques for the separation of different molecules makes this technique adequate for the cleanup of this type of samples. 

Several analytical methods for speciating arsenic have been reported. They include chromatographic techniques such as electrophoresis and ion-exchange (17), paper chromatography (18) and HPLC (19) selective volatilization of arsenic compounds to analogous arsines followed by GC-MES (20) boiling point separation/spectral emission (21) and atomic absorption (22). The above techniques have been applied to samples such as commercial pesticides (20),coal and fly ash (23),rocks, sediments, soils and minerals (24, 22),plant tissue (18), bovine liver (23),and water samples T25). 

Of all the systems which have been utilized for the analysis of pesticide residues, combined gas chromatography-mass spectrometry afiFords a particularly useful approach because positive identification of the components of a mixture can be made without prior separation at sensitivities compatible with the limited quantities of residues generally available. From the results of recent studies involving the application of this technique, it has been demonstrated that available residue analytical methods provide efficient isolation and adequate cleanup of extracts of human, animal, and environmental media in most cases to permit gas chromatographic-mass spectrometric analyses with maximum confidence. Additionally, it has been shown that this combined technique will conveniently provide definitive and conclusive confirmation of residue identity as well as characterization of residues and their metabolites of unknown structure. 

Determination of pesticides in food is very important to ensure human health. Pesticides are especially present in fatty food of animal origin. The sampling process must contain two main steps a preconcentration step made by extrachon of pesticides from the matrix, and a separation step performed by GC or HPLC technique. Choosing the optimum conditions for the first sampling step as well as the best chromatographic technique for discrimination of pesticides assures the best reliability of the analytical information.126127 The most reliable detection system for discrimination of pesticides is MS, which assures both the best selectivity and the best sensitivity for discrimination of pesticides. 

As in other areas of analysis, HPLC is a useful complementary technique to GLC in analyzing pollutants in the environment. An advantage of HPLC in environmental analysis is that molecules of varying polarity (e.g. pesticide + metabolite mixtures) can be analyzed in one chromatographic run. Since aqueous mobile phases can be used in reversed-phase HPLC (including ion-pair partition modes) sample preparation is often less extensive than in GLC. The number of clean-up steps can also be reduced by the use of a precolumn to protect the analytical column or by a preliminary size separation of a crude extract on an exclusion column. 

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