Determination of pesticides in foods

Several methods have been discussed for the determination of method limitations when evaluating procedures for the determination of pesticides in food. A brief comparison of the methods discussed for the determination of the detection and quantification limits of methods used for the analysis of food products can be found in Table 2. 

Lopez-Avila, V., C. Charan, and J.M. Van Emon (1996). Quick determination of pesticides in foods by SFE-ELISA. Food Testing Anal., 2 28-37. 

Pic6, Y., M. Fernandez, M.J. Ruiz, et al. 2007. Current trends in solid-phase-based extraction techniques for the determination of pesticides in food and environment. J. Biochem. Biophys. Methods 70 117-131. 

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. 

Dalliige, J. van Rijn, M. Beens, J. Vreuls, R.J.J. Brinkman U. A.Th. (2002). Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometric detection apphed to the determination of pesticides in food extracts. Jountal of Chromatography A, Vol. 965, No. 1-2, pp. 207-217, ISSN 0021-9673... 

Summary of Analysis Conditions for the Determination of Pesticides in Food from Selected Studies from the Period 2010 to 2013... 

Queiroz, S. C. N., Ferracini, V. L., and Rosa, M. A. 2012. Multiresidue method validation for determination of pesticides in food using QuEChERS and UPLC-MS/MS. Quim. Nova 35 185-192. 

During the recent decades, capillary GC with different sensitive and/or selective detectors has been the most common tool for the multiresidue determination of pesticides in foods. Among these GC systems, the multi-channel mass spectrometer has superseded the element-selective detectors such as BCD and FPD for some years. However, the thermolabile and/or involatile pesticides still remained unavailable for the GC/MS method. On the other hand, it was obvious that the LC/MS suites for such relatively high-polar pesticides. Therefore we developed a MRM using LC/MS which enabled to analyze a total of 50 pesticides consisting of 11 categories (benzoylurea, carbamate, dicarboximide, neonicotinoid, organophosphosphate, oxim carbamate, pyazole, strobilurin, triazole, urea and the others). 

V. Lopez-Avila, C. Charan, and J. van Emon, Supercritical fluid extraction-enzyme-linked immunosorbent assay applications for determination of pesticides in soil and food, in Immunoassays for Residue Analysis Food Safety (R.C. Beier and L.H. Stanker eds), ACS Symposium Series 621, American Chemical Society, Washington (1996). 

The determination of diazinon in foods is important because this chemical is used as a pesticide on plant crops and, at least in some cases, in pesticide dips for the control of parasitic infestations in animals (Brown et al. 1987 Miyahara et al. 1992). Because animals are exposed to this compound, both via pesticide dips and by ingestion of crops to which diazinon has been applied, some methods have been reported for animal products. The majority of methods, however, deal with the determination of residues in plant products. Most of the analytical methods found that describe the extraction from, and determination of, diazinon residues in various crops (plant materials) were developed as part of multiresidue methods. They are based on homogenization of the sample with an organic solvent (polar or non-polar) the isolation of the residues from this initial extract and, usually, some additional cleanup prior to the analysis of the extract by GC. The most common non-MS modes of detection exploit the... 

Table 10.5 Frequency of residues of pesticides in food determined as part of the UK s monitoring programme (data from MAFF 1995-1999)...

The potential of the DPHSE technique for coupling to subsequent operations of the analytical process is only limited by the analyst s ingenuity and material resources. The above-described systems can be combined by altering the sequence of steps and introducing appropriate modifications to develop fully automated systems for specific purposes. Thus, as many as four different steps have been coupled for the determination of pesticides in soil [42] and food [45] (DPHSE, filtration, SPE and HPLC) and that of Hg in soil [42] (DPHSE, SPE, derivatization and detection) in both, the analytical process was conducted in a completely automated manner. 

Other common environmental examples of quantitative GC are in the determination of pesticides in water, dioxin levels in soil and air pollutants. It is routinely used to examine levels of volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). It is also a very important technique in the food industry, where it is used extensively for assay of fatty acids, flavours, sterols and residues such as insecticides, herbicides, preservatives, solvents and veterinary drugs. 

Dagnac, T., Jeannot, R., Mouvet, C., and Baran, N., Determination of chloroacetanilide metabolites in water and soils by LC/ESI-MS. p. 103 in 2nd MGPR international Symposium of pesticides in food and the environment, Valencia (Spain), 9-12 may 2001. 

W.H. Newsome, Determination of Iprodione in Foods by ELISA , in Pesticide Science and Biotechnology, eds. R. Greenhalgh, R. Roberts, Blackwell Scientific, Oxford, 341-352,1987. 

Wang J, Cheung W, Grant D, Determination of pesticides in apple-based infant foods using liquid chromatography electrospray ionization tandem mass spectrometry, J. Agric. Food Chem. 2005 53(3) 528-537. 

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. 

Analysis of pesticide residues is usually performed using GC, and the main field of application of LC is the simultaneous detection of very different pesticides in a single analysis, due to the lack of limitations of volatility or stability compared with GC. Compared with other analyses of minor components of food, determination of residues in food needs lower detection limits and, usually, laborious sample preparation and fractionation before the LC separation can take place. 

Chen, G., Cao, R, and Liu, R. 2011. A multi-residue method for fast determination of pesticides in tea by ultra performance liquid chromatography-electrospray tandem mass spectrometry combined with modified QuEChERS sample preparation procedure. Food Chem. 125 1406-1411. 

January 1992, two working groups have been dealing with analytical methods for the determination of pesticide residues WG 3 Pesticides and PCBs in Fatty Foods and WG 4 Pesticides in Nonfatty Foods . So far analytical methods for 47 pesticides and their metabolites in fatty food and methods for more than 200 pesticides in nonfatty foods have been published in several standards (Table 6). 

Pesticide residues consist of chemicals that might occur in a commodity as a result of application of a pesticide. Such chemicals typically correspond to compounds for which a regulatory agency has or will set a tolerance, i.e., a maximum residue limit, specific to the commodity. In either a field study or a market basket survey, residues to be determined will be those which result from application of the specific pesticide that the study is intended to support. A market basket survey, however, might be intended to support not just one but several different pesticides of the same or different chemical classes. In addition, a market basket survey might include pesticides not used in the USA but for which import tolerances exist. For example, some uses of the parathion family of pesticides on food products have been abandoned in the USA but remain in other countries that export the products to the USA. A market basket survey offers a means to evaluate actual dietary exposures to residues of such pesticides. In addition, tolerance expressions frequently include multiple compounds, all of which must typically be determined in residue field trials. The sponsor of the market basket survey must decide whether to analyze for all compounds in the applicable tolerance expression or to restrict the program to selected analytes, such as the active ingredient. 

Pesticides, including insecticides, herbicides, and fungicides, are widely used in agriculture, and the potential for these residues to accumulate in food has led to concern for human safety. Pesticide residues may enter food animals from environmental sources or from treated or contaminated feeds. Immunoassay development for pesticides has had major impacts for pesticide registrations, analysis of residues in foods, monitoring environmental contamination, determination of occupational exposure, and integration of pest management. 

The use of immunoassays for the determination of pesticides and veterinary medicines in food animals has increased since the early 1990s. The advantages of simple analysis, quick results, and high throughput make immunoassays a powerful technique for problematic matrices commonly encountered in animal agriculture. Careful development and validation are required to obtain accurate results, however. This review has demonstrated that most immunochemical techniques have been designed for use with milk samples, but a number of applications have also been developed for liver and muscle samples. The development of immunoassay techniques for residue analysis in eggs has clearly not been pursued to the extent of other edible tissues. 

Although SPME was applied initially for the analysis of relatively volatile environmental pollutants in waters, rapid developments have enabled SPME to be successfully applied for the analysis of pesticides in water, wine and more complex food samples such as honey, fruit juice and pears, vegetables and strawberries. With food samples, most analysts recognize the need for some sample pretreatment in order to minimize matrix effects. The matrix can affect the SPME efficiency, resulting in a reduced recovery of pesticides. The most common method is simply to dilute the sample or sample extract with water. Simpltcio and Boas comminuted pears in water prior to the determination of pesticides. Volante et al. extracted over 100 pesticides... 

Universal and selective detectors, linked to GC or LC systems, have remained the predominant choice of analysts for the past two decades for the determination of pesticide residues in food. Although the introduction of bench-top mass spectrometers has enabled analysts to produce more unequivocal residue data for most pesticides, in many laboratories the use of selective detection methods, such as flame photometric detection (FPD), electron capture detection (BCD) and alkali flame ionization detection (AFID) or nitrogen-phosphorus detection (NPD), continues. Many of the new technologies associated with the on-going development of instrumental methods are discussed. However, the main objective of this section is to describe modern techniques that have been demonstrated to be of use to the pesticide residue analyst. 

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