Pesticides multi-residue method

Owing to the complexity of multi-residue methods for products of animal origin, it is not possible to outline a simple scheme however, readers should refer to methods described in two references for detailed guidance (Analytical Methods for Pesticides in Foodstuffs, Dutch method collection and European Norm EN 1528. ) There is no multi-method specifically designed for body fluids and tissues. The latter matrix can be partly covered by methods for products of animal origin. However, an approach published by Frenzel et al may be helpful (method principle whole blood is hemolyzed and then deproteinized. After extraction of the supernatant, the a.i. is determined by GC/MS. The LOQ is in the range 30-200 ag depending on the a.i.). 

Moreover, new technologies such as LC/MS/MS should be considered and their potential should be recognized in the future. Currently food control laboratories monitor only a part of the pesticides used in their routine work. They prefer active ingredients that can be analyzed by multi-methods or some group-specific methods, because resources to check all relevant pesticides are normally not available. Therefore, many a.i. are monitored only on a case-by-case basis or not at all. An LC/MS multi-residue method, which may be developed in the future, could cover this gap to a large extent. 

The multi-residue method DFG was intended to be used in state enforcement laboratories or in private contract or food industry laboratories. It was aimed initially only at plant materials and water and included a relatively large number of pesticides which are amenable to GC. 

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. 

Many experts in Europe have tested the methods of both standards with various pesticide-matrix combinations in their own laboratories. Consequently, the responsible working groups of CEN TC 275 concluded that these are the best methods available. Nevertheless, there is no complete validation of all possible pesticide-matrix combinations. However, for most multi-residue methods within the standards all those pesticides which had been successfully tested in method validation trials and/or proficiency tests are listed. Also, matrices which had been examined in ring tests are listed. 

Each individual method collection comprises a large number of methods, which often have different validation statuses. For instance, the most important Swedish multi-residue method (based on ethyl acetate extraction, GPC and GC) is validated for many pesticides by four laboratories, but other methods are presented with singlelaboratory validation data. Some methods in the Dutch and German manuals were tested in inter-laboratory method validation studies, but others by an independent laboratory or in a single laboratory only. 

To reduce the effort, another validation procedure is used for extension of the German multi-residue method to a new analyte. Actually, more than 200 pesticides can be analyzed officially with this method, which is the up-to-date version of the better known method DFG SI9. A typical validation is performed by at least three laboratories, which conduct fortification experiments at the same three levels with at least four representative matrices. These representative matrices are commodities with high water content (e.g., tomato), fruits with high acid content (e.g., lemon), dry crops (e.g., cereals) and commodities with high fat content (e.g., avocado). 

If analytical methods are validated in inter-laboratory validation studies, documentation should follow the requirements of the harmonized protocol of lUPAC. " However, multi-matrix/multi-residue methods are applicable to hundreds of pesticides in dozens of commodities and have to be validated at several concentration levels. Any complete documentation of validation results is impossible in that case. Some performance characteristics, e.g., the specificity of analyte detection, an appropriate calibration range and sufficient detection sensitivity, are prerequisites for the determination of acceptable trueness and precision and their publication is less important. The LOD and LOQ depend on special instmmentation, analysts involved, time, batches of chemicals, etc., and cannot easily be reproduced. Therefore, these characteristics are less important. A practical, frequently applied alternative is the publication only of trueness (most often in terms of recovery) and precision for each analyte at each level. No consensus seems to exist as to whether these analyte-parameter sets should be documented, e.g., separately for each commodity or accumulated for all experiments done with the same analyte. In the latter case, the applicability of methods with regard to commodities can be documented in separate tables without performance characteristics. 

Obviously, a best or generally accepted documentation of performance data of validated multi-residue methods does not exist. Too many data are collected and then-detailed presentation may be confusing and impractical. Additionally, the validation of multi-residue methods is a continuous on-going process which started for many pesticides 20 years ago, when less comprehensive method requirements had to be fulfilled. For this reason, a complete and homogeneous documentation of method validation data cannot be achieved. 

S.L. Reynolds, R. Fussel, M. Caldow, R. James, S. Nawaz, C. Ebden, D. Pendhngton, T. Stijve, and H. Desirens, Intercomparison Study of Two Multi-residue Methods for the Enforcement of EU MRLs for Pesticides in Fruit, Vegetables and Grain, European Commission, BCR Information, Chemical Analysis Contract No. SMT4-CT-95-2030 Reports EUR 17870EN (1997), EUR 18639 EN (1998), EUR 19306 EN (2000) and EUR 19443 EN, European Commission, Brussels (2001). 

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%. 

A multi-residue method for 25 selected pesticides including propanil using an SPE disk has also been developed as a rapid screening method for organic contaminants in river, lake and seawater samples. Cig SPE disks are conditioned with 10 mL of acetone for 3 h. Water samples (1L) are allowed to percolate through the disks in order to trap the residues at a fiow rate of 50 mL min under vacuum. Residues trapped in the disks are extracted twice by eluting with 5 mL of dichloromethane-ethyl acetate (1 1, v/v). The more hydrophobic compounds (log/fow>3) seem to show no... 

Crescenzi et al. developed a multi-residue method for pesticides including propanil in drinking water, river water and groundwater based on SPE and LC/MS detection. The recoveries of the pesticides by this method were >80%. Santos etal. developed an on-line SPE method followed by LC/PAD and LC/MS detection in a simultaneous method for anilides and two degradation products (4-chloro-2-methylphenol and 2,4-dichlorophenol) of acidic herbicides in estuarine water samples. To determine the major degradation product of propanil, 3,4-dichloroaniline, the positive ion mode is needed for atmospheric pressure chemical ionization mass spectrometry (APCI/MS) detection. The LOD of 3,4-dichloroaniline by APCI/MS was 0.1-0.02 ng mL for 50-mL water samples. 

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. 

Multi-residue Method S19 of the DFG Manual,including Cieanup Procedure Xll-6 (gel-chromatographic cleanup), has been used successfully in many laboratories because of its broad applicability for the gas-chromatographic determination of pesticide residues in foodstuffs. DFG method S19 is also included in the respective European Standards. Subsequently, a modification of the extraction and partition step has been implemented. The modified method requires less experimental effort and eliminates the use of dichloromethane, which is an undesirable solvent for toxicological and ecological reasons. As the results from validation studies demonstrate,... 

Multi-residue Method 2 Pesticides Analysed with HPLC Procedures, Submethod 1 N-methylcarbamate Pesticides, in Analytical Methods for Pesticide Residues in Foodstuffs, sixth edition. General Inspectorate for Health Protection, Ministry of Public Health, Welfare and Sport, The Hague, pp. 1-10 (1996). 

Recent trends in pesticide analysis in food aims for reduced sample pretreatments or simplified methodologies (as QuEChERS approaches), the use of online purification processes, the use of new adsorbents (such as molecular imprinted polymers (MIPs) and nanomaterials) for the extraction and clean-up processes, and focused on the development of large multiresidue methods, most of them based on LC-MS/ MS. In spite of the relevant role of LC-MS/MS, GC-MS-based methods still play an important role in pesticide analysis in food. Despite the development achieved in the immunochemical approaches, the need for multi-residue methods has supported the development and use of instrumental techniques. 

Thus Bottomly and Baker [133] have described a multi-residue method for the determination of organophosphorus and synthetic pyrethoid pesticides and carbaryl in grain. After extraction with acetone-methanol, the pesticides... 

C. Jansson, T. PMstrom, B.-G. Osterdahl, K.E. Markides, A new multi-residue method for analysis of pesticide residues in fruit and vegetables using LC-MS-MS detection, J. Chromatogr. A, 1023 (2004) 93. 

Some methods in use are multi-residue methods in which PCBs along with many other analytes such as pesticides, are determined. In general, PCB methods analyze for Aroclor mixtures, PCB homologs, or individual PCB congeners. Until recently, packed column GC/ECD was used most often for the determination of PCBs as Aroclor mixtures. The Webb-McCall technique was used for quantitation. 

Multi residual method for gas chromatography analysis of pesticides in honeybees cleaned by gel permeation chromatography. J. Chromatogr. A 905, 223-232. 

Volmer et al. studied phenylureas and sulfonylureas by TSP-LC-MS after sample concentration by Cjg SPE [175]. 15 phenylurea- and 1 thiourea pesticides besides 112 polar pesticides from other pesticide classes were examined by TSP ionisation, detection limits and TSP mass spectra of these polar compounds were presented [245], Besides other polar pesticides, the phenylurea pesticides isoproturon and diuron were on-line concentrated on a precolumn from several surface and drinking water samples and then determined by TSP-LC-MS [247]. A multi-residue TSP-LC-MS method was published by Moore et al. for the determination of the urea pesticides chlortoluron, diuron, isoproturon, and Unuron in water samples after Cig-SPE [248]. Ci8 Empore disks were applied to concentrate phenylureas from river water and spiked seawater samples prior to TSP-LC-MS. Detection limits of 2-20 (ig L and recoveries between 80 and 125% were observed [239]. TSP-LC-MS (SIM) in the positive mode allowed determination of the urea pesticides chlor-bromuron, diuron, linuron, metobromuron, monuron, neburon in apples, beans, lettuce, peppers, potatoes and tomatoes with detection limits of 0.025-1 ppm [255]. 20 other polar pesticides, linuron, which was under suspicion of being a dietary oncogenic risk (US Natl. Res. Council) was determined by TSP-LC-MS a single rapid procedure in vegetables with detection limits of 0.05-0.10 ppm [270]. TSP-LC-MS and ESI were used in a multi-residue method for determination of the sul-... 

Despite the important advances in fast LC, food matrices are very complex, and although in general multi-residue methods with minimal sample manipulation are demanded, sample extraction and clean-up treatments must be carefully developed to also reduce the total analysis time. The most recently introduced sample treatment methodologies for pesticide residue analysis have also been addressed, with QuEChERS being the most popular one for its easy application and good results. However, other alternatives, such as online SPE or the use of more selective methods such as MIP, are also being applied for the analysis of pesticides. 

Chen, G., Cao, R, and Liu, R. 2011. A multi-residue method for fast determination of pesticides in tea by ultra performance liquid chromatography-electrospray tandem mass spectrometry combined with modified QuEChERS sample preparation procedure. Food Chem. 125 1406-1411. 

Chen, L., Song, R, Zheng, Z., Xing, J., Liu, Z., and Liu, S. 2012. Studies on the determination method of pesticide multi-residues in ginseng by ultra performance liquid chromatography tandem mass spectrometry. HuaxueXuebao 70 843-851. 

Femandez-Alba, A. R., and Garcia-Reyes, J. F. 2008. Large-scale multi-residue methods for pesticides and their degradation products in food by advanced LC-MS, Trends Anal. Chem. 27 973-990. 

Ferrer, I., and E. M. Thurman. 2007. Multi-residue method for the analysis of 101 pesticides and their degradates in food and water samples by liquid chromatography/time-of-flight mass spectrometry. J. Chromatogr. A 1175 24-37. 

An early article by Gimther and Blinn (72) outlined the basic principles of pesticide residue analysis, including the possibilities for systematization and standardization of analytical methods. In many respects this thinking led to the evolution of today s methods, both single residue (SRM) and particularly integrated multi-residue methods (MRMs) that can include several hundred individual anal es, both parent compounds and significant breakdown products (13). 

Hiemstra M, de Kok A. Comprehensive multi-residue method for the target analysis of pesticides in crops using liquid chromatography—tandem mass spectrometry. J Chromatogr A 2007 1154 3-25. 

Ferrer I, Thurman EM (2007) Multi-residue method for the analysis of 101 pesticides and their degradates in food and water samples by liquid chromatography/time-of-flight mass spectrometry. J Chromatogr A 1175(l) 24-37. doi 10.1016/j.chroma.2007.09.092 Ferrer I, Femandez-Alba A, Zweigenbaum JA, Thurman EM (2006) Exact-mass library for pesticides using a molecular-feature database. Rapid Commun Mass Spectrom 20(24) 3659-3668. doi 10.1002/rcm.2781... 

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

Keywords pesticides food multi-residue method high throughput QuEChERS SRM (selected reaction monitoring) H-SRM (enhanced resolution selected reaction monitoring) MS/MS confirmation QED data-dependent acquisition... 

The superior selectivity and high-speed acquisition rate of the GC-MS/MS technique allows interference-free quantification, even with peak co-elution and provides positive confirmation in a single analytical run. To accurately monitor pesticide residues, a high throughput multi-residue method that can quantitate a large number of pesticide residues during a single analysis is described. 

Quick Easy Cheap Effective Rugged Safe, acronym for a East and easy multi-residue method employing acetonitrile extraction/partitioning and dispersive solid-phase extraction for the determination of pesticide residues in produce , www.quechers.com, M. Anastassiades, S.J. Lehotay, D. Stajnbaher and F.J. Schenck, J AOAC Int 86, (2003) 412. 

The best way to test the practicability of the multi-residue approach is to start with the GC determination step. Most often the inability to vaporize the intact compound means that it is not possible to include a new pesticide in the multi-residue scheme. In the case of common moiety methods, a decomposition step is needed to produce the common analyte. Often for that step, modification of the reaction conditions (such as pH and temperature) are necessary, which would lead to a significant deviation from standard multi-residue procedures. 

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