Sample QuEChERS method

The QuEChERS method was invented and described for the first time in 2003 by Anastassiades et al. [98] as a fast, simple, inexpensive, and convenient preparation procedure for fruit and vegetable samples used for pesticide multiresidue analysis. Currently, this methodology is used for determinations of pesticides, pesticide residues, and other compounds of environmental concern such as phenol derivatives, perfluorinated compounds, and chlorinated hydrocarbons pharmaceutical compounds in food and agricultural matrices and environmental samples such as soil, sediments, and water (see for example [99-102]). 

QuEChERS, which stands for Quick, Easy, Cheap, Effective, Rugged, and Safe, is one of those new-generation sample preparation methods for pesticide multiresidue analysis [1]. Although very recently introduced (development between 2000-2002, publication in 2003), the method has been widely embraced by the international pesticide residue analysts community and is already being used in numerous laboratories worldwide [2-6]. Aiming to deliver an economical and... 

Selectivity of partitioning The addition of citrus buffering salts to elevate the pH of sour fruits has also dramatically reduced the amount of co-extractives in the raw extracts. This observation was also made during the development of the original QuEChERS method where the peaks of fatty acids as well as of maleic and fumaric acid in full-scan GC/MS became smaller as the pH of acidic samples... 

Sampling, sample handling, and storage and sample preparation methods are extensively covered, and modern methods such as accelerated solvent extraction, solid-phase microextraction (SPME), QuEChERS, and microwave techniques are included. Instrumentation, the analysis of liquids and solids, and applications of NMR are discussed in detail. A section on hyphenated NMR techniques is included, along with an expanded section on MRI and advanced imaging. The IR instrumentation section is focused on FTIR instrumentation. Absorption, emission, and reflectance spectroscopy are discussed, as is ETIR microscopy. ATR has been expanded. Near-IR instrumentation and applications are presented, and the topic of chemometrics is introduced. Coverage of Raman spectroscopy includes resonance Raman, surface-enhanced Raman, and Raman microscopy. 

The extraction of milk samples was done by the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method [13], modified by adding disodium ethylene-diaminetetraacetate dihydrate (Na2-EDTA). Without any further cleanup, the extract was separated on HPTLC silica gel plates modified by Na2-EDTA. The development was performed with chloroform/methanol/ammonium hydroxide solution (25%), 60/35/5 (v/v/v), followed by fluorescence densitometry (ELD) at 366 nm/<400 nm... 

A popular approach for sample treatment is the QuECHERS method, which is gaining increasing recognition in PRA laboratories [12]. It is based on the use of acetonitrile (ACN) and MgS04 for salting-out... 

Special focus has been set to the widely used and popular sample preparation methods as there are the pressurized liquid extraction (RLE), the thermal extraction of materials and food (outgassing), and in detail on the QuEChERS pesticide sample preparation used for GC-MS and LC-MS. As a consequence of the higher matrix load of these extracts and the recommended GC injection techniques, concurrent backflush, preventive maintenance and inlet deactivation became current topics of discussion. Olfactometry solutions have been added for apphcations in flavour analysis. 

Lesueur, C., R Knittl, M. Gartner et al. 2008. Analysis of 140 pesticides from conventional farming foodstuff samples after extraction with the modified QuEChERS method. Food Control. 19 906-914. 

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. 

Golge, O., Kabak, B. Evaluation of QuEChERS sample preparation and liquid chromatography-triple-quadrupole mass spectrometry method for the determination of 109 pesticide residues in tomatoes. Food Chem. 176, 319-332 (2015)... 

The QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) method allows the extraction of a wide variety of pesticides from polar and basic (methamidophos, acephate, omethoate, imazalil and thiabendazole) to less polar, such as pyrethrins. Samples of homogenized grape (lOg) are extracted with 10 mL of acetonitrile. After shaking for 1 min, 4 g of anhydrous MgS04 and 1 g of NaCl are added and mixed. One milliliter of the acetonitrile aliquot is transferred to a 1.5 mL vial... 

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. 

Lehotay, S. J. 2011. QuEChERS sample preparation approach for mass spectrometric analysis of pesticide residues in foods. Methods Mol. Biol 747 65-91. 

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. 

In order to evaluate the performance of the three selected methods, wheat blank samples spiked at 50 (Xg/kg were treated, applying the three procedures showing the obtained results. It can be observed that the best results were obtained when QuEChERS procedure was used, allowing the extraction of more than 80 compounds with suitable recoveries (70-120%) and relative standard deviation (RSD) lower than 20%. When the ultrasound method was applied, more than 80 compounds were extracted, but only 36 compounds, including all the mycotoxins and biopesticides assayed in this study, were quantitatively extracted, whereas this approach was not suitable for most of the selected pesticides. Finally, an intermediate situation was obtained when the procedure described by Mol et al. was applied. More than 50 compounds were extracted with recoveries ranging from 70% to 120% and RSD values lower than 20%. 

For analytical studies, sample preparation is necessary to determine the composition of phenolic compounds in these matrices. The most widely used extraction system is UAE, which is an inexpensive method since it involves the use of low organic solvent and requires short extraction times. Multi-analyte methods with minimal sample manipulation are demanded. However, vegetables and fruits are very complex matrices and hence sample extraction and clean-up treatments must be carefully developed to reduce manipulation and total analysis time. Therefore, QuEChERS could be a useful tool for this purpose in future applications. 

The popular multi-component methods with short sample preparation and extract clean-up such as QuEChERS require special care for the chromatographic... 

Dirty matrix samples of multi methods such as QuEChERS. 

DTCs are not stable and cannot be extracted or analyzed directly. Contact with acidic plant juices degrades DTCs rapidly and they decompose into carbon disulfide (CS2) and the respective amine (Crnogorac and Schwack, 2009). DTCs cannot be extracted by organic solvents from homogenize plant samples, as it is the QuEChERS standard procedure in pesticide-residue analyses. The described method is a non-specific DTC sum method that does not distinguish between the different species of DTCs in the sample. Interferences are known from natural precursors, for example from crops or brassica, that can produce CS2 as well during hydrolysis (Reynolds, 2006 Crnogorac and Schwack, 2009). 

Pesticide analysis with multi-methods using single and triple quadrupole instruments and QuEChERS sample preparation... 

---