Cleanup methods,pesticide

Sample Cleanup. The recoveries from a quick cleanup method for waste solvents based on sample filtration through a Elorisd and sodium sulfate column are given in Table 2 (40). This method offers an alternative for analysts who need to confirm the presence or absence of pesticides or PCBs. 

Shibata Y, Oyama M, Sato H, et al. 1998. Simultaneous cleanup method for multi pesticide residue analysis by GC and HPLC. J Food Hyg Soc Jpn 39(4) 241-250. 

Marble LK, Delfino JJ. 1988. Extraction and solid phase cleanup methods for pesticides in sediment and fish. American Laboratory 23-32. 

TABLE 7.1 PERCENT PESTICIDE RECOVERY WITH VARIOUS CLEANUP METHODS 1 (9)... 

Several cleanup methods have been developed for the determination of urea pesticides, involving different basic procedures, such as liquid-liquid partition (30-32,34,36,37), steam distillation (31), and liquid-solid chromatography (9,30,32,34,36,38,56-58). Different factors, e.g., water solubility, ionic and polarity properties, thermal stability, and the molecular weight of the compounds, determine the choice of the cleanup method. Moreover, micro-cleanup procedures and online enrichment techniques have been introduced for the automated determination of phenylureas (60). Table 6 summarizes the use of the different cleanup procedures in the determination of urea pesticides. 

A bibliographic search has shown that the majority of the HPLC techniques for determining OPPs and OCPs have been applied to the determination of residues in surface, ground- and drinking water. Table 5 lists pesticides determined, extraction and cleanup methods used, HPLC conditions, contaminated matrix and analyte detection limits taken from the literature for water, animal tissues, milk, fruit and vegetables, and cereals. The majority of the studies were done on spiked samples, and in the best of cases there were few real samples analyzed. 

Sulfur is found in many industrial wastes, marine algae, and sediment samples. Sulfur may mask the region of chromatogram, overlapping with peaks of interest. For example, in pesticides analysis, sulfur can mask over many pesticides such as lindane, aldrin, and heptachlor. Sulfur has a solubility similar to the organochlorine and organophosphorus pesticides and it cannot be separated by Florisil cleanup method. 

The solvent extracts can be cleaned up by traditional column chromatography or by solid-phase extraction cartridges. This is a common cleanup method that is widely used in biological, clinical, and environmental sample preparation. More details are presented in Chapter 2. Some examples include the cleanup of pesticide residues and chlorinated hydrocarbons, the separation of nitrogen compounds from hydrocarbons, the separation of aromatic compounds from an aliphatic-aromatic mixture, and similar applications for use with fats, oils, and waxes. This approach provides efficient cleanup of steroids, esters, ketones, glycerides, alkaloids, and carbohydrates as well. Cations, anions, metals, and inorganic compounds are also candidates for this method [7],... 

European Corrrmittee for Standardization. CEN Guideline EN 1528-3, Fatty Food — Determination of Pesticides and Polychlorinated Biphenyls (PCBs). Cleanup Methods, General, Beuth, Berlin, 1997. 

Solid-phase extraction (SPE) using small, disposable cartridges, columns, or disks is employed for isolation and cleanup of pesticides from water and other samples prior to TLC analysis, especially using reversed-phase (RP) octa-decyl (C-18) bonded silica gel phases. Microwave-assisted extraction (MAE) is a time- and solvent-saving method for removing residues from samples such as soils. Supercritical fluid extraction (SEE) has been used for sample preparation in the screening of pesticide-contaminated soil by conventional TLC and automated multiple development (AMD). Ultrasonic solvent extraction (USE) and videodensitometry have been combined for quantification of pesticides in sod. Matrix solid-phase dispersion (MSPD) with TLC and GC has been used to determine diazinon and ethion in nuts. 

In this context, studies about the development of relevant analytical methods allowing the detection of pesticide residues in VOO are usually focused on an optimization of the various steps of the analysis process, namely extraction, clean-up, identification, and quantitation of pesticide content. The common extraction methods are Soxhlet extraction, microwave-assisted extraction (MAE), supercritical fluid extraction (SEE), and accelerated solvent extraction (ASE). Cleanup methods include SPE, matrix solid-phase dispersion (MSPD), and gel permeation chromatography (GPC). 

Using HPTLC, a new and efficient cleanup method was recently developed for pesticide residue analysis. The technique was established for extracts of fruit and... 

The analysis of pesticides in samples of high color content needs the optimization of cleanup parameters. Carrots, spinach, and apple extracts were extracted with acetone, partitioned into methylene chloride, and finally purified on a mixed adsorbent column (Table 1). The loadability of the TLC plates and the effectiveness of this cleanup method were tested not only by GLC but by TLC as well (23). TLC can be used as a detection method, as a test of the cleanup (see above), and furthermore can be applied as a cleanup procedure (16). In MCPA (4-chloro-2-methylphenoxyacetic acid) analysis the recovery data showed that TLC cleanup was as effective as H20-toluene partitioning. 

Keywords multi-residue method pesticides fruits vegetables SPE cleanup single quadrupole MS. 

T. Cairns and J. Sherma, eds.. Emerging Strategiesfor Pesticide Analysis, CRC Press, Boca Raton, Fla., 1992, 368 pp. From the series Modem Methods of Pesticide Analysis, presents survey of improvements in extraction and cleanup, detailed descriptions of alternative analytical methods, latest appHcations, and up-to-date references. 

Residue analytical chemistry has extended its scope in recent decades from the simple analysis of chlorinated, lipophilic, nonpolar, persistent insecticides - analyzed in the first Si02 fraction after the all-destroying sulfuric acid cleanup by a gas chro-matography/electron capture detection (GC/ECD) method that was sometimes too sensitive to provide linearity beyond the required final concentration - to the monitoring of polar, even ionic, hydrophilic pesticides with structures giving the chemist no useful feature other than the molecule itself, hopefully to be ionized and fragmented for MS or MS" detection. 

The methods EN 1528 1996 and EN 12393 1998 comprise a range of old multiresidue methods of equal status, which are widely accepted throughout Europe. These are, e.g., the Luke method and the German Deutsche Forschungsgemeinschaft (DFG) methods S8 and S19 ° (all based on extraction with acetone), the Association of Official Analytical Chemists (AOAC) method 970.52 (using acetonitrile extraction and liquid-liquid partition combined with Horisil column cleanup) and the Dutch ethyl acetate extraction combined with GPC. All methods have been subjected to inter-laboratory studies, although not with all pesticide/matrix combinations, which would be impossible to achieve. 

For multi-analyte and/or multi-matrix methods, it is not possible to validate a method for all combinations of analyte, concentration and type of sample matrix that may be encountered in subsequent use of the method. On the other hand, the standards EN1528 andEN 12393 consist of a range of old multi-residue methods. The working principles of these methods are accepted not only in Europe, but all over the world. Most often these methods are based on extractions with acetone, acetonitrile, ethyl acetate or n-hexane. Subsequent cleanup steps are based on solvent partition steps and size exclusion or adsorption chromatography on Florisil, silica gel or alumina. Each solvent and each cleanup step has been successfully applied to hundreds of pesticides and tested in countless method validation studies. The selectivity and sensitivity of GC combined with electron capture, nitrogen-phosphorus, flame photometric or mass spectrometric detectors for a large number of pesticides are acceptable. 

T. Pihlstrom, B- Kajrap, and A. Valverde, ValidationdataforlSpesticidesincludedinthemulti-residue method for analysis of pesitddes in fruit and vegetable using ethyl acetate extraction, GPC cleanup and GC determination, in Pesticide Analytical Methods in Sweden , Part 1, Rapport 17/98, National Food Administration, Uppsala (1998). 

A multi-residue method based on SPE cleanup and gas chromatography/ion trap mass spectrometry (GC/ITMS) was developed for the determination of 120 pesticides and related metabolites in two soils with organic matter contents of 4.0-5.2%. 

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. 

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. 

The use of SPE with porous materials such as alumina, diatomaceous earth, Horisil and silica for the cleanup of fat-soluble organochlorine pesticides in fatty foods such as meat, flsh, shellfish, milk and vegetable oils has been well documented. The choice of elution solvents is critical because relatively small amounts of lipid in the final extract can cause rapid deterioration of GC capillary columns and also contaminate the gas chromatograph. A number of workers have used a porous material in tandem with Cig to effect an improved cleanup.Di Mucchio employed a multicartridge system comprising Extrelut, silica and Cig to extract organophosphorus pesticides from oils and fatty extracts. Relatively few literature applications include the pyrethroids, but Ramesh and Balasubramanian reported a simple carbon-based SPE method for the analysis of pyrethroids in vegetable oil. 

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