Carbamates cleanup

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. 

A preliminary cleanup procedure is often required for most food sample extracts before determination by HPLC. The goal of cleanup is to remove as much interfering coextracted material and as little analyte as possible. Due to the wide range of polarities of carbamate pesticides, it is difficult to develop one cleanup procedure equally effective for all of them. Therefore, the cleanup procedure will depend on the type of compound, the kind of sample to be analyzed, and the selectivity of the analytical equipment used in the determination. The use of selective detectors can reduce or even eliminate the need for cleanup procedures in some cases. 

A variety of adsorbents, such as alumina, silica gel, Florisil, and various activated carbons, have been employed for carbamate residue cleanup (43). Liquid chromatography on alumina (44-46), silica gel (14), or Florisil (47) has also been used as a cleanup step. 

Liquid-liquid extraction has also been employed as a cleanup step, with separations being made between an acid or alkaline aqueous phase and an organic solvent (48). This procedure takes advantages of differences in the physical and chemical characteristics between the carbamate and the substrate. Another commonly used procedure is based on the generally high solubility of carbamates in polar solvents and their low solubility in saturated hydrocarbons. Table 5 summarizes the use of the various cleanup procedures in the determination of carbamate pesticides. 

Table 5 Cleanup Procedures for Sample Extracts Used in the Determination of Carbamate Pesticides...

The analysis of cell culture media and supernatants, as well as non-standard protein hydrolysates such as collagens and glycoproteins, has created the demand for techniques that accurately quantify additional amino acids not normally found in hydrolyzed samples, Methods of amino acid analysis (AAA) based on precolumn derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) have previously been shown to quantify hydrolyzed samples with a high degree of accuracy (1,2). The AQC-based method has also been shown to derivatize effectively in the presence of salts and lipids (3). Taking into account the above strengths, the excellent stability of the derivatives, and the unique fluorescence properties that allow for direct injection of the reaction mixture without cleanup, the AQC methodology represents an ideal choice for the analysis of complex samples. 

The extraction, cleanup and derivatization of carbamate pesticides are reviewed in this section. Their automation and online coupling with chromatographic instruments is also dealt with here. 

Carbamate Pesticides Environmental Samples Extraction Technique cleanup Technique Reagent/Other Pretreatment Detection Chromatographic Column Analytical Figures of Merit Ref. 

In the past, TLC and spectroscopy were the firsts analytical techniques used for the determination of carbamate pesticides, with their inherent difficulties (particularly their limited sensitivity). With the inception of GC and LC, TLC applications were restricted to sample cleanup, metabolic studies, and, perhaps most important, confirmatory analyses in clinical and medical-legal cases requiring positive, unambiguous identification, and quantitative determination.At present, TLC continues to offer attractive features, such as, parallel sample processing for a high sample throughput, accessibility of the sample for postchromatographic evaluation free of time constraints, detection in the presence of the stationary phase, which is somewhat independent of mobile phase and normally used only once. Table 24.5 shows selected examples of the use of TLC for the determination of carbamates. 

Carbamate Environmental Extra ction/Cleanup Reagent/Other stationary Phase/- Analytical Figures D... 

Micellar chromatography shows promise for the separation of labile dilhiocarbamate species with metabolites of toxicological significance, which are commonly employed as pesticides, and hence, may be present in industrial effluents. Conventional methods for the determination of dithio-carbamates are susceptible to interferences and require carefiil sample cleanup procedures prior to derivatization, to obtain accurate and reproducible results. 

OP), and carbamate pesticides are available as standard methods by the AO AC covering both nonfatty and fatty foods. These methods are based on solvent extraction and a variety of column chromatographic cleanup procedures with determination by GC using selective detectors. The International Dairy Federation has approved similar methods for OC and OP pesticide residues in milk and milk products. The AOAC have standard methods for specific pesticides or groups of pesticides that are approved for certain foodstuffs these methods involve colorimetric, spectrophotometric, or gas chromatographic determination. In the case of me-thylcarbamate pesticides, a liquid chromatographic method is approved. 

Yang, R. Z, Wang, J. H., Wang, M. 1., Zhang, R., Lu, X. Y., and Liu, W. H. 2011. Dispersive solid-phase extraction cleanup combined with accelerated solvent extraction for the determination of carbamate pesticide residues in radix glycyrrhizae samples by UPLC-MS-MS. J. Chromatogr. Sci. 49 702-708. 

Eight carbamate pesticides were analyzed in bovine rumen. The method was based on extraction, partition, and an addititmal sweep condistillation step. This cleanup gave more re oducible results compared to cellulose-carbon column cleanup. The spots were visualized with either anisaldehyde or lV,2,6-trichloto-benzoquinoneimine after reversed-phase TLC (68). Carbamate and urea herbicides such as chlorpropham, metobromuron, and chlorbromuron were determined in medicinal plants by TLC. First they were hydrolyzed by alkali to 3-chloro-, 4-bromo-, and 3-chloro-4-bromoaniIines. These aniline derivatives were detected with 4-dimethylaminobenzaldehyde after TLC separation (Table 4) (69). Af-methyl carbamate pesticides can be separated by reversed-phase chromatography and analyzed by MS (70). 

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