Extraction techniques QuEChERS

Most of the extraction techniques of phenolic compounds from vegetables are based on ultrasound-assisted extraction (UAE) [27,44,45], In addition, other techniques have been successfully applied to the pretreatment of phenolic compounds in fruits and vegetables, including pressurized liquid extraction (PLE) [46], solid-phase extraction (SPE) [47], supercritical fluid extraction (SFE) [48], microwave-assisted extraction (MAE) [49], rotary shaker-assisted extraction (RAE), [50] and QuEChERS (acronym of quick, easy, cheap, effective, rugged and safe) [51], as can be observed in Tables 16.3 and 16.4. In some cases, an acid treatment [52] was applied to hydrolyze the glycosides in order to determine the content of free and conjugated flavonoids as aglycons. 

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. 

Kaufmann et al. developed a bipolarity extraction method based on principles similar to those of the QuEChERS technique. With the use of this isolation technique, polar and non-polar residues remained in the aqueous phase and underwent clean-up by SPE on a mixed-mode Oasis HLB cartridge. The residues were subsequently analyzed by UPLC-MS/MS. Extracts isolated using the bipolarity approach required a lengthy SPE procedure prior to analysis. Kaufmann stated that extracts produced at the end of the procedure contained less matrix components compared to QuEChERS. However, it can be concluded that... 

As the QuEChERS-extracts are solved in acetonitrile, they are directly amenable to GC- and LC-applications. However, since acetonitrile is rather difficult to handle by GC using split/splitless inlets, the use of a PTV with solvent vent possibility is highly recommended. Should a PTV not be available and the desired pesticide detection limits cannot be achieved using the split/splitless technique, extract concentration followed by a solvent exchange, if necessary, may be considered. If GC-MSD is employed, a simple evaporative concentration of the extracts by a factor of four should be sufficient. To achieve this, e.g., a 4-mL extract (acidified to pH 5) is transferred into a test tube and reduced to ca. 1 mL at 40 °C using... 

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. 

Matrix solid-phase dispersion (MSPD) is an SPE variant where samples are ground and mixed with a support. In the initial application, samples were placed in a disposable column previously packed with Florisil, which trapped the fat from the sample and allowed the compounds of interest to be eluted. This has successfully been applied to the determination of lipophilic pesticides from both fatty and non-fatty matrixes. Recently, an orthogonal technique, dispersive solid-phase extraction, for the isolation and analysis of a variety of pesticides on numerous food matrixes has been introduced. The technique is called QuEChERS, which stands for quick, easy, cheap, effective, rugged, and safe. The technique offers advantages in time and solvent usage since it uses approximately 10 ml of solvent per sample when compared to the potentially hundreds of milliliters of solvent used for more standard extraction and isolation protocols. It uses a combination of MgS04 and primary secondary amine (PSA) sorbent not only to remove water and non-target compounds, but also isolate the compounds of interest. 

An alternative sample preparation is based on the QuEChERS (Quick Easy Cheap Effective Rugged Safe) technique [14]. In this the sample is extracted into acetonitrile and magnesium sulfate, sodium chloride and citrate buffer salts at pH 5-5.5 are added, the mixture is shaken and then centrifuged to separate the phases. When applied to honey [15] the samples, containing isoproturon-d6 as an internal standard, were diluted with water and homogenized before addition of the QuEChERS salts described above, and acetonitrile. After extraction, centrifugation... 

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. 

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