About the Method
During the development of the method the principal aim was to make it as stream-lined as possible by avoiding complicated and time consuming analytical steps.
History
The QuEChERS method was developed by Michelangelo Anastassiades in the years 2001 and 2002 during his post-doc visit at the USDA/ARS-ERRC in Wyndmoor/Pennsylvania (USA) in the research group of Steven Lehotay. Initially the methodology was developed for the analysis of veterinary drugs (anthelmintics and thyreostats) in animal tissues but after realizing its great potential in the extraction of polar and particularly basic compounds it was also tested on pesticide residue analysis in plant material with great success.
The new method for the analysis of pesticide residues in plant material was first presented in June 2002 at the EPRW 2002 in Rome (M. Anastassiades, S.J. Lehotay, D. Stajnbaher: „Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) approach for the determination of pesticide residues“). The detailed method was first published in 2003 (M. Anastassiades, S. J. Lehotay, D. Stajnbaher, F.J. Schenck, JAOAC Int 86(2) 412-31 (see Literature).
The pesticide residue laboratory of the CVUA Stuttgart has been using QuEChERS (original version) for routine pesticide analysis of fruit and vegetables since the beginning of 2002 and has employed it for the first time in EU-PT 4 on orange matrix (2002) with excellent results.
The original method was modified in the following years to enlarge both, pesticide and commodity scope. Of great importance was the introduction of buffering salts to improve recoveries of pH-dependant analytes. Lehotay, S. J., K. Mastovska, et al., J AOAC Int 88(2): 615-29, (see Literature) have introduced acetate buffering to achieve a pH value of 6 for all samples. This approach resulted in the official method AOAC 2007.01.
At the CVUA Stuttgart Anastassiades et al. refined QuEChERS using citrate salts for buffering, and elaborated conditions to allow the analysis of various difficult commodities and pesticides. The citrate buffered method resulted in the European Standard EN 15662 (Foods of Plant Origin – Determination of Pesticide Residues Using GC-MS and/or LC-MS/MS Following Acetonitrile Extraction/Partitioning and Clean-up by Dispersive SPE (QuEChERS method)) published in 2008 (see CEN – European Committee for Standardization).
Great amount of data was generated by various laboratories around the world to validate the QuEChERS method. Given the large amount of data a special database has been developed to allow the systematic storage and selective retrieval of the validation data of QuEChERS and other methods. This database is incorporated in the EURL-datapool webpage and already contains more than 120.000 individual recoveries concerning ca. 650 pesticides and metabolites. Access requires registration.
In the last years numerous research groups worked with QuEChERS and expanded the scope of analytical applicability of the method for example for natural contaminants, veterinary drugs, mycotoxins and other fields.
Theory
Many pesticide multiresidue methods (MRMs) used are complicated, laborious, time-consuming, require high amounts of solvents and are therefore expensive. Considering that the time spent for instrumental analysis is also continuously growing due to the introduction of new analytes and instrument techniques, laboratories are not able to analyze the number of samples they would like to. In addition, some important analytes can not be satisfactorily covered by many common MRMs (e.g. basic, acidic and very polar compounds). In order to cover such analytes, laboratories have to additionally perform laborious single analyte methods, which is often not possible. This results in a large grey area of pesticides which are not routinely monitored by most laboratories.
In the last decade there has been a general trend to develop faster analytical methods. The automated instrument based extraction procedures SFE and ASE, which were introduced in the mid 1990s to speed up extraction, did not succeed to replace traditional multiresidue approaches. Ideally, a multiresidue method should be fast and easy to perform, require a minimum amount of chemicals, provide a certain degree of selectivity to avoid complicated cleanup procedures and still cover a sufficiently broad spectrum of analytes. Analysts accustomed to performing complex traditional analytical procedures often hesitate to switch to simpler ones assuming that a simpler and faster analytical procedure can not be accurate enough and should, if at all, only be used for screening procedures. In reality, however, the more analytical steps a procedure entails and the more complicated it is the more likely is the introduction of systematic and random errors.
During the development of the method the principal aim was to make it as stream-lined as possible by avoiding complicated and time consuming analytical steps.
| Time-Consuming, Complicated or Error-prone Steps | Simplified Alternatives |
|---|---|
| Sample Processing/HomogenizationSimplified | No Way Around this |
| Blending (e.g. with Ultra-Turrax) | Shaking |
| Filtration | Centrifugation |
| Multiple Partitioning Steps | Single Partitioning (“Online”-Approach) |
| Separation/Transfers of Entire Extract | Take Aliquots (Use ISTD) |
| Use of a Lot of Glassware | Extraction/Partitioning in Single VesselLarge |
| Evaporation/Reconstitution | Large Volume Injection; Sensitive Instrument |
| Classical StepsClassical SPE with Columns & Manifold | Dispersive SPE |
The entire method was published from Anastassiades and Co-workers in the Journal of AOAC INTERNATIONAL in 2003 (see Literature).
QuEChERS Workflow
Reality
Since its introduction, the QuEChERS method has been readily accepted by many pesticide residue analysts. Some modifications to the originally published method had to be introduced to ensure efficient extraction of pH-dependent compounds (e.g. phenoxyalcanoic acids), to minimize degradation of susceptible compounds (e.g. pesticides labile under alkaline and acidic conditions) and to expand the spectrum of matrices covered. Buffering with citrate salts has been introduced in the first extraction/partitioning step to adjust the pH to a compromise value of 5 to 5.5, where most pesticides labile under acidic or alkaline conditions are sufficiently stabilized. To improve stability of alkaline-labile compounds after PSA clean-up the final sample extracts are slightly acidified by adding a small amount of formic acid. Acidic pesticides are directly analysed from the raw extract before PSA clean-up. For samples with high chlorophyll content, a mixture of PSA and GCB (Graphitized Carbon Black) is used for clean-up at amounts, where some residual chlorophyll still remains in the final extract. Dry commodities such as cereals, dried fruits or tea require the addition of water prior to extraction to weaken interactions of pesticides with the matrix and to ensure adequate partitioning. Even commodities with a high lipid load, such as avocados or plant oils are amenable to this procedure. However, due to a partition to the lipid phase, highly non-polar pesticides give relatively low but typically consistent recoveries (< 70 %). Co-extracted lipids in the extracts can be removed to a high degree by a freezing-out step or a C18 clean-up.
USA
AOAC Official Method 2007.01
Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate.
Europe
prEN 15662 Version 2007-10-24
Foods of Plant Origin — Determination of Pesticide Residues Using GC-MS and/or LC-MS/MS Following Acetonitrile Extraction/Partitioning and Clean-up by Dispersive SPE (QuEChERS-method).
For several commodities specific modifications of QuEChERS method are necessary.
Avocado
is a matrix containing both high amount of fat and water, therefore water is added prior to extraction and fat is removed by freezing out.
» Avocado (pdf)
Plant oil can be analyzed using QuEChERS method by directly adding acetonitrile to 2 g oil. Only very unpolar pesticides like HCB or DDT have recoveries below 70 %. Residual fat is removed by freezing out before PSA cleanup.
» Oil (pdf)
Black tea is a very difficult matrix having a lot of co-extractives. Therefore additional cleanup is necessary. For black tea a combination of PSA and CaCl2 improves cleanup procedure.
» Tea (pdf)
The
organotin pesticides Fentin, Cyhexatin and Fenbutatin oxide have very good recovery rates using QuEChERS method. For LC-MS/MS analysis however, acidic conditions are of paramount importance to achieve good peak shapes.
» Organotin Pesticides (pdf)
Base-labile compounds like Captan, Folpet, Dichlofluanid and others degrade in QuEChERS extracts after PSA cleanup. Therefore the extracts have to be acidified using formic acid to a pH of about 5 to stabilize these base-labile compounds.
» Base-labile Pesticides (pdf)
Acid-labile compounds like Ethoxyquin or Pymethrozine partly degrade at a pH of 5. For these pesticides trisodium citrate is used instead of the normally used citrate salt combination.
» Acid-labile Pesticides (pdf)
Using citrate buffer enables the inclusion of
acidic pesticides in the compound spectrum. For the acids PSA-cleanup has to be avoided, and the raw extract is directly used for analysis. Even an alkaline hydrolysis can be included to cover bond residues or esters.
» Acidic Pesticides (pdf)
Analysis of
Abamectin
via QuEChERS and LC-MS/MS
» Abamectin (pdf)
Analysis of
Amitraz
and its main metabolite N-2,4-Dimethylphenyl-N-Methylformamidine in pears via QuEChERS and LC-MS/MS
» Amitraz (pdf)
Modified QuEChERS
method for the analysis of
Chlorothalonil
in fruits and vegetables
» Chlorothalonil (pdf)
Analysis of
Nicotine
in mushrooms via modified QuEChERS
method
» Nicotine (pdf)
Analysis of
Pentachlorophenol (PCP) in guar gum by modified QuEChERS
method
» Pentachlorophenol (pdf)
Quality
The QuEChERS method has proofed its quality in several European Union Proficiency Tests for Fruits and Vegetables (EUPT-FV). The results are shown for the years 2003–2005 and 2006–2008, respectively.
A large number of validation and recovery experiments also showed that QuEChERS is a reliable method.
An online version of QuEChERS Validation Data is available for registered users via EURL DataPool.