Advantages pesticide analysis

Possible Contributions of Immunochemical Methods to Pesticide Analysis. As Ercegovich (3 ) pointed out, it is unlikely that immunochemical methods will replace current, established analytical methods of pesticide analysis. However, the analytical chemist who carefully compares the attributes and deficiencies of immunochemical methods of analysis with other procedures is likely to find applications for which immunochemical methods offer distinct advantages. 

It is probable that in certain situations immunochemical methods will provide distinct advantages over conventional analytical methods. However, it is unlikely that immunochemical methods will completely replace current, established analytical methods of pesticide analysis (5.). This is in spite of the fact that chemical classes currently assayed by immunochemical techniques in clinical analytical labs contain the same type of functional groups as many pesticides. 

Liquid chromatographic systems for environmental pesticide analysis have been extensively reviewed in a previous paper. Nowadays, LC is the technique of choice for analyzing those pesticides which, being thermolabile, are not amenable to direct GC analysis, such as phenylurea and SUHs. LC methods of analysis also have the important advantage over GC methods in that online pre- and postcolumn reaction systems are compatible with LC instrumentation. Furthermore, the LC apparatus can easily be coupled online with the enrichment step using SPE on precolumns, thereby making the analysis fully automated. 

On the other hand, the QuEChERS (quick, easy, cheap, effective, rugged, and safe) method, originally developed for pesticide analysis [23], has been also applied to the determination of multiclass veterinary drugs in different food commodities [24—27], The conventional QuEChERS strategy applies acetonitrile extraction, followed by removal of water and proteins by salting out with sodium chloride and magnesium sulphate. Afterwards, dispersive SPE (d—SPE) is usually applied. The QuEChERS approach has many advantages, as it is simple and quick, reduces the... 

Two steps have been added to the original Pesticide Analytical Manual method to increase the stability of the trimethylsilyl derivatives and to clean up the final extract prior to GC analysis, namely the use of a sodium sulfate mini-column to dry the extract after derivatization and the use of a Florisil Sep-Pak cartridge to remove matrix interferences. The advantages of the current method are the simultaneous evaluation of the four analytes, reproducibility and low matrix interference. 

Sample preparation techniques vary depending on the analyte and the matrix. An advantage of immunoassays is that less sample preparation is often needed prior to analysis. Because the ELISA is conducted in an aqueous system, aqueous samples such as groundwater may be analyzed directly in the immunoassay or following dilution in a buffer solution. For soil, plant material or complex water samples (e.g., sewage effluent), the analyte must be extracted from the matrix. The extraction method must meet performance criteria such as recovery, reproducibility and ruggedness, and ultimately the analyte must be in a solution that is aqueous or in a water-miscible solvent. For chemical analytes such as pesticides, a simple extraction with methanol may be suitable. At the other extreme, multiple extractions, column cleanup and finally solvent exchange may be necessary to extract the analyte into a solution that is free of matrix interference. 

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. 

There are a large number of literature references that refer the use of SPE cartridges for the extraction of pesticides from water. There are several comprehensive reviews of the use of SPE, including that by Soriano et al. who discussed the advantages and limitations of a number of sorbents for the analysis of carbamates. Hennion reviewed the properties and uses of carbon based materials for extraction of a wide multiclass range of pesticides. Thorstensen et al. described the use of a high-capacity cross-linked polystyrene-based polymer for the SPE of phenoxy acids and bentazone, and Tanabe et al reported the use of a styrene-divinylbenzene copolymer for the determination of 90 pesticides and related compounds in river water. SPE cartridges are also widely used for the cleanup of solvent extracts, as described below. 

For detection, MS is rapidly becoming the method of choice for multiclass, multiresidue analysis owing to its many advantages, recent improvements in technology, and availability of cost-effective commercial instrumentation. Detection systems in general are continually being improved, and in combination with the improvements in chromatographic instruments and techniques, an exceptionally low limit of detection (LOD) is possible for pesticide residues. 

Polymeric precolumns of styrene-divinylbenzene were used by Aguilar et al. to monitor pesticides in river water. Water samples (50 mL) were trace enriched on-line followed by analysis using LC combined with diode-array detection. LC atmospheric pressure chemical ionization (APCI) MS was used for confirmatory purposes. It was found that after the pesticides had been extracted from the water sample, they could be stored on the precartridges for up to 3 months without any detectable degradation. This work illustrates an advantage of SPE for water samples. Many pesticides which may not be stable when stored in water, even at low temperature, may be extracted and/or enriched on SPE media and stored under freezer conditions with no detectable degradation. This provides an excellent way to store samples for later analysis. 

While deterministic methods are still quite useful in determining long-term, chronic exposures to pesticides, they are being replaced with probabilistic methods for the analysis of acute (short-term) exposures. These probabilistic methods take advantage of improvements in computational capabilities. 

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