Microwave-assisted extraction characteristics

Table 3.26 Characteristics of closed-vessel microwave-assisted extraction...

The impact of the extraction conditions using various solvents on the recoveries has never been studied in detail, and the results have never been compared. The introduction of modern extraction methods, such as microwave-assisted extraction, supercritical fluid extraction, and solid-phase extraction, probably will improve the efficiency of extraction, even in the instance of unstable pigments and pigment mixtures. The majority of TLC separations were carried out on traditional silica layers. As the chemical structures and, consequently, the retention characteristics of pigments are highly different, a wide variety of eluent systems has been employed for their separation, consisting of light petroleum, ethyl formate, ethyl acetate, benzene, toluene, chloroform, methanol, n-butanol, formic or acetic acid, and so forth. 

Table 7.2 Characteristics of solvents commonly used in microwave-assisted extraction. From Dean, J. R., Extraction Methods for Environmental Analysis, Copyright 1998. John Wiley Sons Limited. Reproduced with permission...

ATR-FTIR The fibers were washed with water under microwave assisted extraction for an hour and then analyzed by ATR-FTIR spectroscopy. A Thermo Nicolet Magna 550 single bounce FTIR spectrometer equipped with a Thermo-Spectra-Tech Foundation Series Diamond ATR with Deuterated Triglycine Sulfate (DTGS) detector was used for this study. The characteristic peak at wavenumber 1656 cm corresponds to the -C=0 stretch in the amide functional groups in PAAm. 

Principles and Characteristics Pare et al. [475] have patented another approach to extraction, the Microwave-Assisted Process (MAP ). In MAP the microwaves (2.45 GHz, 500 W) directly heat the material to be extracted, which is immersed in a microwave transparent solvent (such as hexane, benzene or iso-octane). MAP offers a radical change from conventional sample preparation work in the analytical laboratory. The technology was first introduced for liquid-phase extraction but has been extended to gas-phase extraction (headspace analysis). MAP constitutes a relatively new series of technologies that relate to novel methods of enhancing chemistry using microwave energy [476]. 

---