Pesticides extraction methods

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). 

Extraction of residues from soil samples is much more difficult than their extraction from plant or water samples. The pesticide residues in the soil exist often in several forms as bound residue , which may affect the extraction efficiency of pesticides from the soil. Then, various extraction methods such as organic solvent extraction, Soxhlet extraction, sonication extraction, microwave dissolution and supercritical fluid extraction (SEE) are used. Some extraction methods are described in the following. 

Thus, organic solvent extraction methods for the extraction of pesticides from water samples can be replaced by the SPE method using Ci8 and PS-2. Ethobenzanid, clomeprop, naproanilide and their acidic metabolites are determined by a multi-residue analytical method using Cig or PS-2 cartridge extraction after acidification of the water samples with hydrochloric acid or other acidic media, followed by HPLC or LC/MS detection. 

The fundamental issue is to describe how much of the residue can be characterized accurately and whether an accounting of the applied mass of pesticide can be maintained throughout the course of the experiment. A series of environmental fate studies is required for pesticide registration in order to characterize the degradation pathways and formation and decline patterns of each major degradate. These studies are typically conducted in the laboratory under controlled conditions, applying radiolabeled pesticides to evaluate the extraction efficiency of various procedures. When standard extraction methods fail to release a significant amount of the applied radioactivity, more efficient and exhaustive extraction procedures are tried in a stepwise fashion... 

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 development of a robust analytical method is a complex issue. The residue analyst has available a vast array of techniques to assist in this task, but there are a number of basic rules that should be followed to produce a reliable method. The intention of this article is to provide the analyst with ideas from which a method can be constructed by considering each major component of the analytical method (sample preparation, extraction, sample cleanup, and the determinative step), and to suggest modern techniques that can be used to develop an effective and efficient overall approach. The latter portion emphasizes mass spectrometry (MS) since the current trend for pesticide residue methods is leading to MS becoming the method of choice for simultaneous quantitation and confirmation. This article also serves to update previous publications on similar topics by the authors. ... 

Alba et al. used ethyl acetate to extract imidacloprid residues from fruits and vegetables. A 15-g sample of vegetable or fruit is weighed into a blender tube and 60 mL of ethyl acetate and 15g of sodium sulfate are added. The mixture is homogenized for 30 s, using a Polytron, and filtered. The filtrate is evaporated and the residue obtained is dissolved in acetonitrile-water (1 1, v/v). Alba etal. considered the low recoveries of these polar pesticides as the major disadvantage of the acetone extraction method. In their previous work they evaluated the efficacy of ethyl acetate for the extraction of pesticide residues. 

SFE. SFE has been established as the extraction method of choice for solid samples. The usefulness of SFE for soil samples has been demonstrated for carbamate,organophosphorus and organochlorine pesticides. However, SFE is more effective in extracting nonpolar than polar residues. In order to obtain a greater extraction efficiency for the polar residues of imidacloprid, the addition of 20% methanol as modifier is required. Extraction at 276 bar and 80 °C with a solvent consisting of supercritical carbon dioxide modified with methanol (5%) for 40 min gives a recovery of 97% (RSD = 3.6%, n = 10). It is possible to use process-scale SFE to decontaminate pesticide residues from dust waste. ... 

A. YagJ, Y. Asano, and K. Ishikawa, Extraction method for fenothiocarb in sods, in Abstracts of the 5th Annual Meeting of the Pesticide Residue Analysis Society, pp. 35-38 (1981) (in Japanese). 

Ahnoff and Josefsson [18] built a solvent extraction apparatus for river work which was later modified into their in situ extractor [ 17]. The unit as described in the earlier work could easily be adapted for seawater analysis. A unit based on a Teflon helix liquid-liquid extractor, some 332 feet (101.5 metres) in length, was constructed by Wu and Suffet [19]. The extractor was optimized for the removal of organophosphorus compounds, specifically pesticides, with an efficiency of around 80%. For some compounds, these continuous extraction methods should be the methods of choice and should be explored. 

In the adsorption with Tenax alone satisfactory results were obtained, while in the presence of mineral oil a considerable proportion of the organophos-phorus pesticides (particularly Malathion and Parathion-methyl) was not adsorbed and was recovered in the filtered water. This drawback can be overcome by adding a layer of Celite 545 which, in order to prevent blocking of the column, is mixed with silanised glass wool plugs. A number of analyses of surface and estuarine sea waters were carried out by this modified Tenax column and simultaneously by the liquid-liquid extraction technique. To some of the samples taken, standard mixtures of pesticides were also added, each at the level of 1 xg/l (i.e., in concentration from 13 to 500 times higher than that usually found in the waters analysed). One recovery trial also specifically concerned polychlorobiphenyls. The results obtained in these tests show that the two extraction methods, when applied to surface waters that were not filtered before extraction, yielded very similar results for many insecticides, with the exception of compounds of the DDT series, for which discordant results were frequently obtained. 

Due to the predicted and previously detected low concentrations of pesticides in environmental samples (usually around the nanogram per liter level), a preconcentration step of the water samples is necessary prior to measurement. In this way, a preconcentration factor of several orders of magnitude (200-1,000-fold) is mandatory to reach the low detection limits necessary for the identification of pesticides, especially in complex wastewater samples. Also, the use of surrogate standards (e.g., triphenyl phosphate) added before the extraction step is a common practice in order to account for possible errors during the extraction process and for quantitative purposes. The commonly used extraction methods for polar compounds from water matrices involve isolation using liquid-liquid extraction (LLE) and solid-phase extraction (SPE), which are commented on below. Other methods such as semipermeable membrane devices (SPMD) are also mentioned. 

The popularity of this extraction method ebbs and flows as the years go by. SFE is typically used to extract nonpolar to moderately polar analytes from solid samples, especially in the environmental, food safety, and polymer sciences. The sample is placed in a special vessel and a supercritical gas such as CO2 is passed through the sample. The extracted analyte is then collected in solvent or on a sorbent. The advantages of this technique include better diffusivity and low viscosity of supercritical fluids, which allow more selective extractions. One recent application of SFE is the extraction of pesticide residues from honey [27]. In this research, liquid-liquid extraction with hexane/acetone was termed the conventional method. Honey was lyophilized and then mixed with acetone and acetonitrile in the SFE cell. Parameters such as temperature, pressure, and extraction time were optimized. The researchers found that SFE resulted in better precision (less than 6% RSD), less solvent consumption, less sample handling, and a faster extraction than the liquid-liquid method [27]. 

Djordjevic MV, Hofmann D, Fan J. 1994. Assessment of chlorinated pesticides and polychlorinated biphenyls in adipose breast tissue using a supercritical fluid extraction method. Carcinogenesis 15(11) 2581-2585. 

LC techniques are widely diffused for the determination of hydrophilic but not volatile and thermally unstable pesticides. Since the European Community Directive [68] indicates 0.1 pg L" as the concentration threshold level for a single pesticide in waters destined for human consumption, to quantify these concentration levels, suitable pre-concentration and extraction procedures must be generally performed prior to the HPLC determination. The extraction methods are based on LLE, MAE, on-line continuous flow liquid membrane extraction (CFLME), and mainly on SPE and SPME. Many SPE procedures are used the packing materials are graphitized carbon, ODS, styrene-divinylbenzene co-polymers, or selective phases based on immunoafflnity. The extraction can be performed on- and off-line, manually, or in a semi-automated way. 

As mentioned, for the production of pharmaceutical products, the roots of P. ginseng are not uniform in their content of ginsenosides (markers and active ingredients of the plant) and the content of pesticides can be too high in some cases. Therefore, the use of cultivated plants (with a rational use of pesticides) and standardized extraction methods are basic to ensuring the uniformity of an extract and thus its consistent pharmacological and toxicological effect. 

Liquid-solid extraction methods coupled to LC-DAD are gaining interest for the screening of pesticides in waters. Automated precolumn technology involving disposable solid-phase extraction precolumns has proved to be a useful tool. A C18 precolumn was used online by LC-DAD. In these conditions, 11 OPPs were analyzed in groundwater (49). 

Turin, H.J. and R.S. Bowman (1993). A solid-phase extraction based soil extraction method for pesticides of varying polarity. J. Environ. Qual., 22 332-334. 

Environmental research interests have recently extended from persistent hydrophobic organic chemicals to more hydrophilic organic compounds. The latter include some polar pesticides, many pharmaceuticals and personal care products, microbial toxins, and endocrine disrupting compounds.4 Polar organic compounds are often present at low concentrations in the aquatic environment, which poses a problem for most conventional sampling and analytical procedures. Recently, considerable effort has been directed toward the development of extraction methods suitable for the preconcentration of polar organic compounds commonly found in water bodies. Many of these methods use... 

For pesticides not included in the Pharmacopoeial list, a formula based on the Acceptable Daily Intake (ADI) for the particular chemicals, as published by the Food and Agriculture Organisation (FAO-WHO), is used to determine the permitted level. The Pharmacopoeia recognises that many pesticides are poorly soluble and that an extraction method used to produce extracts, tinctures etc. can modify the content of pesticides in the finished product. In such cases the calculation of the limit includes an extraction factor. 

In another. similar example [8] France et al. used a bed of activated alumina in the extraction vessel downstream of the sample itself to "scrub-out" (retain) the hpids while allowing hpophilic pesticides extracted from a grain sample to pass on to the collection/reconstitution device to produce a hpid-free fraction to pass on to a GC/ECD for analysis of the pesticides. This is particularly important since hpids must normaUy be removed from pesticide-containing extracts by long and tedious manual-column methods, evaporation and solvent exchange. 

Van der Velde, E.G., W. de Haan, and A.K.D. Liem. 1992. Supercritical fluid extraction of polychlorinated biphenyls and pesticides from soil. Comparison with other extraction methods. J. Chromatogr. 626 135-143. 

EPA method 3562, Supercritical Fluid Extraction of Polychlorinated Biphenyls (PCBs) and Organochlorinated Pesticides, Test Methods for Evaluating Solid Waste, EPA, Washington D.C., 1996. 

The principal extraction methods enabling standard 1000-fold concentration of pesticides in a final reduced volume of solvent (generally 1 ml) are described below. 

Other selective extraction methods applied to some pesticides, such as molecularly imprinted polymer extraction, could be extended to organophosphoms compounds. 

The Main Extraction Methods Used for Determining Organophosphorus Pesticides in Soils and Some Data... 

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