Sample Pretreatment with Microwave-Assisted Techniques

Abstract

Traditional methods of sample preparation for organic analytes, such as Soxhlet extraction and sonication, are both timeconsuming and create large amounts of solvent waste. Typical extractions take up to 6 h to complete, and use well over 100 ml of chlorinated organic solvent. Although newly developed supercritical fluid extraction (SFE) has enjoyed much success owing to its organic solvent-free extraction using non-toxic CO2 as the supercritical solvent, its extraction results depend not only on the solute, but also on the sample matrix. Moreover, more polar hazardous fluids are often required to combine with the organic modifiers to effect complete extraction. In many analytical laboratories, the microwave-assisted dissolution technique is already the method of choice for sample preparation. Other microwave-assisted techniques for sample preparation are being constantly developed and put into practice. The application of microwave energy for the isolation of organic analytes from diverse samples began in the mideighties, and has made great progress with the advent of commercial microwave systems. 1 Compared with the traditional sample preparation methods, microwave-assisted extraction (MAE) is rapid (generally 5 -10 min), solvent saving (generally 20 -30 ml of non-chlorinated organic solvent.) and efficient.Recently, we have developed a series of microwave-assisted techniques for sample pretreatment prior to GC, GC-MS or HPLC determination of target organic analytes in diverse samples. The microwave-assisted experiments were performed with a 600 W microwave sample preparation system (Model MK-1, Xin-Ke Institute of Applied Microwave Technology, Shanghai, China). The operating conditions could be optimized by mainly adjusting three parameters, namely, the magnetron power output, usually set at 100%, the irradiation time (or heating time) and the controlled pressure value. The pressure in the vessel could be indicated by a special-designed optical fiber sensor. There were eight separate stages for pressure selection, and a pressure as high as 4 MPa could be attained. The volume of the PTFE lined digestion vessel was about 60 ml. The turntable could hold nine vessels simultaneously.GC determinations of PAHs, PCBs and triazines were performed on a HP-5 column (0.25 mm, 0.25 µm phase thickness) using a Hewlett-Packard 4890D series gas chromatograph equipped with an electron-capture detector (ECD), a nitrogen phosphorus detector (NPD) and a split/splitless injector operated in the splitless mode. The chromatograph data were obtained and processed in a HP Chemstation (G2070AA, A.04.01).A HP6890 series gas chromatography interfaced to a HP 5973 mass-selective detector with a HP MS Chemstation data system (G1701AA, B.02.05) was used for MS identification of the GC peaks. The column used was a HP-5Ms cross-linked fusedsilica capillary column (30 m × 0.25 mm, 0.25 µm, phase thickness) coated with 5% phenyl-polymethylsiloxane. The HPLC used for the analyses of triazines was a Shimadzu LC-4A with an SPD-1 UV-VIS detector. ...

Fast and accurate preparation fatty acid methyl esters by microwave-assisted derivatization in the yeast Saccharomyces cerevisiae

“…Recently, there has been growing interest to speed up reaction of chemical synthesis by microwave irradiation in different applications (Söderholm et al 2010). The applications of microwave-assisted derivatization to prepare FAMEs from fatty acids (free and bound fatty acids) can be found in various types of biological samples, i.e., edible oil, bacterial cells, animal tissue, and plasma samples (Zhang et al 2000;Tomas et al 2009;Itonori et al 2004;Jeyashoke et al 1998;Liebeke et al 2010). However, there has been no attempt to establish a proper method for FAME preparation in yeast samples.…”

Microwave-Assisted Extraction of Quercetin and Acid Degradation of Its Glycosides in Psidium Guajava Leaves

“…Microwave-assisted techniques have evolved into very attractive sample preparation methods in the last two decades. 4,5 The general principle of microwave heating has been described elsewhere. 6 In brief, microwave-assisted techniques utilize the microwave heating effect that originates mainly from rotation of molecules with dipole moments and migration of ions, or in other words, originates from the ability of polar solvents to transform the absorbed electromagnetic energy into heat.…”

Determination of Volatile Compounds in Magnolia Bark by Microwave-Assisted Extraction Coupled to Headspace Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry

“…5,6 In this decade, microwave energy was investigated and is being widely applied in analytical chemistry for purposes such as accelerating sample digestion and extraction, and also in chemical reactions. [7][8][9][10][11] The popularity of this technique is due to the rapid rates of heat transfer provided by microwave heating, which allows quicker times of analysis of analytes in complex samples compared to more traditional Soxhlet or liquid extractions, but with similar results realized. 12 Therefore, microwave heating has the potential to improve HS-SPME sampling for volatile compounds.…”