Microwave-assisted extraction solid matrices

Theoretical and applied aspects of microwave heating, as well as the advantages of its application are discussed for the individual analytical processes and also for the sample preparation procedures. Special attention is paid to the various preconcentration techniques, in part, sorption and extraction. Improvement of microwave-assisted solution preconcentration is shown on the example of separation of noble metals from matrix components by complexing sorbents. Advantages of microwave-assisted extraction and principles of choice of appropriate solvent are considered for the extraction of organic contaminants from solutions and solid samples by alcohols and room-temperature ionic liquids (RTILs). 

Microwave-assisted extraction (MAE) of analytes from various matrices using organic solvents has been operative since 1986 [128], In this process microwave energy is used to heat solvents in contact with a solid sample uniformly and to partition compounds of analytical interest from the sample matrix into the solvent. The way in which microwaves enhance extraction is not fully understood. The main factors to consider include improved transport properties of molecules, molecular agitation, the heating of solvents above their boiling points and, in some cases, product selectivity. 

Microwave-assisted extraction (MAE) it has attracted growing interest, as it allows rapid extraction of solutes from solid matrices by employing microwave energy as a source of heat [42], The portioning of the analytes from the sample matrix to the extractant depends upon the temperature and the nature of the extractant. 

Keywords Pressurized liquid extraction supercritical fluid extraction ultra-sound-assisted extraction microwave-assisted extraction matrix solid-phase extraction high-performance liquid chromatography gas chromatography liquid-liquid extraction solid phase extraction column chromatography... 

A variety of solvent extraction techniques have been used to extract antioxidants from food matrices. The most commonly used is maceration or homogenization of the sample with an extraction solvent however, alternative procedures have been developed including pressurized fluid extraction (PFE), ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), and matrix solid-phase dispersion (MSPD), among others. The principles of each extraction technique will be briefly discussed. 

Most studies about the microwave-assisted extraction of PAHs from solid samples have been conducted using closed-vessel systems [12,214,226,236,239-246] and only a few with open-vessel focused microwave devices [57,247-252]. Because open-vessel systems operate at atmospheric pressure, the extraction vessel can be used as a reactor in order to perform on-line purification pretreatments of the total extracts (reagents can be readily added to the medium) [53] or directly introduce the extract into the determination instrument, as in the focused microwave-assisted extractor with on-line fluorescent monitoring of Fig. 5.10, which provides a matrix-independent approach to the extraction of PAHs [61]. 

First of all, it is important to identify what the acronyms represent. The following have been used aMAE, atmospheric microwave-assisted extraction SFE, supercritical fluid extraction pMAE, pressurized microwave-assisted extraction PFE, pressurized fluid extraction ASE, accelerated solvent extraction MSPD, matrix solid-phase dispersion. 

Even though the interest in microwave-assisted extraction (MAE) has increased during the last 10 years, this technique has not been utilized much in food and feed applications. Only a few papers can be found with the combination of POPs and food/feed samples. This may be because MAE applications frequently require laborious and tedious clean-up of the extracts before final analysis. In some cases, only a simple filtration or centrifugation may be sufficient to separate the solid matrix from the extract but since MAE most often is more exhaustive than selective, extensive clean-up procedures based on for example solid-phase extraction is commonly needed for removal of interfering compounds (73-75). Other techniques that have been used for clean-up of MAE extracts are gel permeation chromatography (75), solid-phase micro extraction (77, 78), and liquid-liquid extraction (79). 

The procedure to be used to extract carbamate pesticides from environmental samples depends on their polarity and on the type of sample matrix involved. Various choices exist for the extraction of pesticides ranging from conventional procedures (e.g., Soxhlet extraction, liquid-liquid extraction (LLE), evaporation, steam distillation) to new methodologies including solid-phase extraction (SPE), solid-phase microextraction (SPME), supercritical fluid extraction (SEE), matrix solid-phase dispersion (MSPD), accelerated solvent extraction (ASE) and microwave-assisted extraction. " ... 

Extraction of herbicides from solid matrixes has frequently been done by Soxhlet extraction, which required large volumes of solvent and was a time consuming process. Therefore, new extraction techniques have been developed and applied for the past ten years. Herbicides and their main metabolites can be extracted from sohd samples by these new methods such as, SFE, subcritical water extraction (SWE), microwave-assisted extraction (MAE), or pressurized fluid extraction (PFE). From a general point of view. Camel evaluated potentials and pitfalls of SEE, MAE, and PFE. ... 

Camel, V. (2001). Recent extraction techniques for solid matrixes — Supercritical fluid extraction, pressurized fluid extraction, and microwave-assisted extraction Their potential pitfalls. Analyst 126, 1182-1193. 

Solid-phase extraction (SPE) using small, disposable cartridges, columns, or disks is employed for isolation and cleanup of pesticides from water and other samples prior to TLC analysis, especially using reversed-phase (RP) octa-decyl (C-18) bonded silica gel phases. Microwave-assisted extraction (MAE) is a time- and solvent-saving method for removing residues from samples such as soils. Supercritical fluid extraction (SEE) has been used for sample preparation in the screening of pesticide-contaminated soil by conventional TLC and automated multiple development (AMD). Ultrasonic solvent extraction (USE) and videodensitometry have been combined for quantification of pesticides in sod. Matrix solid-phase dispersion (MSPD) with TLC and GC has been used to determine diazinon and ethion in nuts. 

In this context, studies about the development of relevant analytical methods allowing the detection of pesticide residues in VOO are usually focused on an optimization of the various steps of the analysis process, namely extraction, clean-up, identification, and quantitation of pesticide content. The common extraction methods are Soxhlet extraction, microwave-assisted extraction (MAE), supercritical fluid extraction (SEE), and accelerated solvent extraction (ASE). Cleanup methods include SPE, matrix solid-phase dispersion (MSPD), and gel permeation chromatography (GPC). 

The mode of extraction for PAHs is highly dependent on the matrix. For solid-based matrices such as food samples, sediments, soil, marine organisms, etc. extraction methods such as Soxhlet extraction with nonpolar solvent [35 6], hollow fiber membrane solvent microextraction (HFMSME) [10], pressimzed hquid extraction (PLE) [37,38], sonication extraction [3], microwave-assisted extraction (MAE) [3], supercritical fluid extraction, (SEE) [39], accelerated solvent extraction (ASE) [40], cold extraction [41], soxtec extraction [42], microwave-assisted alkaline saponification (MAAS) [43], dynamic microwave-assisted extraction (DMAE) [44], add-induced cloud point extraction (ACPE) [45], methanolic saponification extraction (MSE) [7], etc. are employed. Of all these, Soxhlet extraction is the most common for solid samples and has achieved excellent extraction with high-level recovery but its setback is the high consmnption of solvent and time associated with it. 

Saponification—Liquid-hquid extraction Soxhlet extraction Ultrasound-assisted extraction Microwave-assisted extraction Pressurized liquid extraction Supercritical fluid extraction Matrix solid-phase dispersion... 

Depending on the complexity of the sample matrix, a pre-cleaning step is a possible solution to remove interfering eflFects nevertheless, the choice should be a good compromise in relation to the total time and cost of analysis [33]. Supercritical fluid- [48,49], microwave-assisted- [50] or solid-phase extraction (SPE) [51-53] have been used as pre-cleaning steps prior to immunoassay. However, in certain situations, the extraction step led to a decrease in accuracy and recovery, probably due to analyte loss during clean-up/ evaporation/re-dissolution steps [53]. 

Garcia-Ayuso, L. E., Luque-Garcia, J. L., and Luque de Castro, M. D., Approach for independent-matrix removal of polycyclic aromatic hydrocarbons from solid samples based on microwave-assisted Soxhlet extraction with on-line fluorescence monitoring. Ana/. Chem., 72, 3627-3634, 2000. 

A, acaricide AV, avicide I, insecticide F, fungicide H, herbicide GR, growth regulator N, nematocide R, rodenticide US, ultrasonication LLE, liquid-liquid extraction CU, cleanup ImCU, immuno cleanup SPE, solid-phase extraction MSPD, matrix solid-phase dispersion SBSE, stir bar sorptive extraction SD, steam distillation FMSE, focused microwave Soxhiet extraction PFE, pressurized fluid extraction ASE, assisted solvent extraction ScFE, subcritical fluid extraction SFE, supercritical fluid extraction SEC, size-exclusion chromatography LC, liquid chromatography (fraction collection) LTLP, low temperature lipid precipitation. 

For many years, the traditional sample preparation methods, such as the Soxhlet extraction, were applied. Most of these methods have been used for more than 100 years, and they mostly require large amounts of organic solvents. These methods were tested during those times, and the analysts were familiar with the processes and protocols required. However, the trends in recent years are automation, short extraction times, and reduced organic solvent consumption. Modern approaches in solid sample preparation include microwave-assisted solvent extraction (MASE), pressurized liquid extraction, accelerated solvent extraction (ASE), matrix solid-phase dispersion (MSPD), automated Soxhlet extraction, supercritical fluid extraction (SEE), gas-phase extraction, etc. 

The classical approach to extract PAHs from lipophilic compounds which are abundant in marine matrices is by means of saponification in basic (NaOH or KOH) alcoholic solution [indicatively see (Webster et al. 2006 Rank 2(X)9)] or the Soxhlet extraction with organic solvents mainly acetone, n-hexane and DCM [indicatively see (Vorkamp et al. 2010 Yoshimine et al. 2012)]. Both methods are widespread, but time consuming. For this reason more fast methods which reduce time, labour and solvent use were pursued by researchers. These include Sonication Assisted Extraction (Maioli et al. 2010 Dsikowitzky et al. 2011), Microwave Assisted Liquid Extraction (MAE) (Cortazar et al. 2008 Zuloaga et al. 2009), and Accelerated Solvent Extraction or Pressurized Liquid Extraction (ASE) usually conducted with the Dionex system (Sloan et al. 2004). Finally the matrix solid-phase dispersion (MSPD) has also been applied to extract PAHs from mussels even in miniaturized scale (Campins-Falco et al. 2008). 

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