Microwave energy matrices

MAE simply involves placing the sample with the solvent in specialized containers and heating the solvent using microwave energy. MAE is also sometimes called MASE, which can stand for microwave-assisted solvent extraction or microwave-accelerated solvent extraction. In any event, the extraction process is more rapid than Soxhlet extractions, can be run in batches, and reduces solvent consumption. As in the case of sonication, MAE may overcome retention of the analyte by the matrix, but analyte degradation can be a problem at higher temperatures in certain applications. 

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. 

The principle of FMW involves the heating of both the solvent and the matrix by wave/matter interactions. The microwave energy is converted into heat by two mechanisms dipole rotation and ionic conductance. The heating is, therefore, selective with only polar or moderately polar compounds susceptible. Due to the use of low microwave energy the structure of target molecules remains intact. 

MAP makes use of physical phenomena that are fundamentally different compared to those applied in current sample preparation techniques. Previously, application of microwave energy as a heat source, as opposed to a resistive source of heating, was based upon the ability to heat selectively an extractant over a matrix. The fundamental principle behind MAP is just the opposite. It is based upon the fact that different chemical substances absorb microwave energy... 

Residual moisture content of samples can play a major role in reproducible sampling of the matrix, as well as in the interaction of the microwave energy with the sample. 

Microwave solidification is an ex situ mixed-waste treatment process. The process is applicable for homogeneous, wet or dry, inorganic solids. The process dries the waste, mixes it with a matrix modifier, transfers it to a processing container, and subjects the mixture to microwave energy to melt the materials. The processed waste form then cools and solidifies to form crystalline mineral analogs. 

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. 

In microwave assisted extraction (MAE), microwave energy accelerates the partition, i.e. the mass transfer of an analyte from a sample matrix into a solvent, by directly heating the solution. The extraction is performed at an elevated temperature in a closed vessel. The major benefits are the shorter extraction time, reduced consumption of organic solvents and increased sample throughput. However, there is a need for an additional filtration step and, if the extract is dilute, further concentration, e.g. by evaporation or SEE, may be needed before analysis. 

This method is similar to ASE. except that healing power is supplied by microwaves. MASE has been used for the extraction of pesticides from soil supercritical fluid extraction of CM pesticides from soil. Lopez-Avila ei al. (1998) studied the stability of OCs and OPs when extracted from. solid matrixes with microwave energy. 

Lopez-Avila, V., Benedicto, I., and Bauer, K. M. (1998). Stability of organochlorine and organophosphorous pesticides when extracted from solid matrixes with microwave energy. J. AOAC Int. 81, 1224-1232. 

Aromatic plants are usually constituted from cellulose, essential oil, and water. If these three compounds are heated by microwaves at a fixed radiation power and for a set time, the heating rate will be the highest for water, followed by essential oil and cellulose, respectively. One of the interactions of the microwave energy with the matrix is called the dipolar polarization mechanism. A substance can generate heat when irradiated with microwaves if it has a dipole moment, for example that of the water molecule. A dipole is sensitive to external electric fields and will attempt to align itself with the field by rotation. 

Microwave-assisted extraction (MAE) uses microwave energy to heat the solvent/sample mixture in order to partition analytes from the sample matrix into the solvent (see Fig. 4.6). Using microwave energy allows the solvent to be... 

However, most cosmetic samples require a pretreatment like complete acid digestion or leaching of the analytes, which may or may not be relatively difficult depending on how efficiently the analytes are extracted from the matrix. Microwave energy permits rapid heating of samples, which considerably reduces pretreatment time. For example, heavy metals have been determined in some cosmetics (lipsticks, powders) using different atomic spectroscopic techniques after acid treatment assisted by micro-wave irradiation. 

In MASE, the sample and solvent are heated directly, in contrast to more conventional schemes, where the vessel is heated to extract the sample. The MASE technique uses a combination of microwave energy and a pressurized environment to enhance the extraction efficiency of some species. The energy adsorbed in a microwave is based on two complementary phenomena molecular dipole rotation and ionic conductance. The sample solvents are placed in a closed vessel that absorbs microwaves. This facilitates the extraction of the samples of interest and has been applied to a variety of sample types and matrixes, with one of the most notable successes being its use in the automation of sample preparation of environmental samples. Conversely, open vessel microwave heating can be used to reduce solvent volumes and concentrate samples for subsequent analysis. 

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