Pesticide determination

Today, however, GC-GC coupling is seldom used to determine pesticides in environmental samples (2), although comprehensive MDGC has been applied to determine pesticides in more complex samples, such as human serum (19). On the other-hand, new trends in the pesticide market, which is now moving towards the production of optically active enantiomers and away from racemic mixtures, may make this area suitable for GC-GC application. The coupling of non-chiral columns to chiral columns appears to be a suitable solution to the separation problems that such a trend might cause. 

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.

C. Aguilar, P. BottuII and R. M. Marce, On-line and off-line solid-phase extraction with styrene-divinylbenzene-membrane extr action disks for determining pesticides in... 

Most modern methods of analysis to determine pesticide residues in food commodities, whether a multi-residue method (MRM) or a single-residue method (SRM), can be broken down into three or four basic steps sample processing, sample extraction, extract cleanup (optional) and instrumental determination. 

C. Soler, K. J. James, and Y. Pico. Capabilities of Different Liquid Chromatography Tandem Mass Spectrometry Systems in Determining Pesticide Residues in Food Application to Estimate Their Daily Intake. J. Chromatogr., A1157(2007) 73-84. 

Manes J, Font G, Pico Y. 1993. Evaluation of a solid-phase extraction system for determining pesticide residues in milk. J Chromatog 642 195-204. 

Hopper ML, Griffitt KR. 1987. Evaluation of an automated gel permeation cleanup and evaporation systems from determining pesticide residues in fatty samples. J Assoc Off Anal Chem 70 724-726. 

The reason why this combination of principles is so powerful is that Briggs was also able to demonstrate that the key properties discussed in earlier sections which determine pesticide behaviour can be regarded as partitions. Thus solubility may be envisaged as a partition between the compound itself and water, soil adsorption can be treated as a partition... 

Gel permeation chromatography (GPC), also called size-exclusion chromatography, is the most widely used cleanup technique for pesticides in fatty foods. It is the method of choice for rapid cleanup of biological extracts, especially from high-fat samples, to determine pesticide residues, since separation occurs on the basis of molecular size (7). 

A procedure for determining pesticide residues in fruit and vegetable (apples, potatoes, and carrots) using HPLC-UV detection has been reported. A monitoring study in which 40 samples of different origin were examined was carried out. a-Endosulfan was detected in one apple sample, and tetradifon was detected in a potato sample (57). 

One major problem with determining pesticides in real samples is that one or several of a range of pesticides could be present. Therefore we... 

The AHS, a collaborative research effort between the National Cancer Institute of the National Institutes of Health and EPA, is a prospective occupational study of 89,658 pesticide appliers and their spouses in Iowa and North Carolina assembled between 1993 and 1997 to evaluate risk factors for disease in rural farm populations (Blair et al. 2005). It is being conducted in three phases—phase I (1993-1997), phase II (1999-2003), and phase III (2005)—and includes only limited biomonitoring. Data are gathered with questionnaires to determine pesticide use and exposures, work practices, and other relevant exposures from buccal cell collection with dietary surveys and with interviews to determine updated pesticide exposures (Agricultural Health Study 2005). 

Lopez-Avila, V., C. Charan, and W.F. Beckert (1994). Using supercritical fluid extraction and enzyme immunoassays to determine pesticides in soils. Trends Anal. Chem., 13(3) 118-125. 

Rodolico, S., R. Giovinazzo, and M. Mosconi (1997). Comparison between ELISAs and traditional analytical methods to determine pesticide pollution in water. Bull. Environ. Contam. Toxicol., 58 644—650. 

Blasco, C., G. Font, and Y. Pico. 2002. Comparison of microextraction procedures to determine pesticides in oranges by liquid chromatography-mass spectrometry. J. Chromatogr. A 970 201-212. 

Sherma, J. Shafik, T.M. A multiclass, multiresidue analytical method for determining pesticide residues in air. Arch. Environ. Contamin. Toxicol., 1975, 3, 55. 

Of even greater interest are recent reports of the presence of organochlorine pesticides (again principally DDT and its metabolites) in sharks, tuna, and other salt water fish (19). Studies are now under way to determine pesticide levels in fish from all salt water areas of the world to learn... 

In determining pesticides in water by electron capture gas chromatography, laboratory sources of contamination are a major problem. The principal sources of this contamination are described and illustrated in this section. 

A laboratory wishes to establish if its method for determining pesticide residues in fruit is performing satisfactorily. Invariably, most of the fruit samples will not contain any measurable concentration of pesticides. To obtain materials to check the performance of the method, in particular to gain an estimate of the bias, a laboratory could take a portion of unused sample extract that has previously been analysed and add a known amount of pesticide to the matrix. Analysis of this spiked sample will help demonstrate if all the pesticide is being recovered in the analysis or if there is significant interference from the sample matrix. 

Past, Present, and Future Application of Paper and Thin-Layer Chromatography for Determining Pesticide Residues... 

The basic principles of modeling the physical, chemical and biological processes that determine pesticide fate in unsaturated soil are reviewed. The mathematical approaches taken to integrate diffusion, convection, sorption, degradation and volatilization are presented. Deterministic and stochastic models formulated to describe these processes in a soil-water pesticide system are contrasted and evaluated. The use of pesticide models for research or management purposes dictates the degree of resolution with thich these processes are modeled. 

LC-MS/MS is increasingly used to determine pesticides in water. Using this technique in multiple reaction modeling (MRM) mode results in better sensitivity, better quantification limits and improves the identification performance. Generally, in the MS/MS configuration, a triple quadrupole or an ion trap is used. 

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