Environmental Sample Pretreatment with Microwave-Assisted Techniques

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 environmental samples began in mid eighties and has made great progress in recent years. In this work, the microwave-assisted extraction (MAE),the microwave-assisted saponification (MAS) and the microwave-assisted alkaline degradation (MAAD) of organic compounds in various synthetic and real environmental samples are described.     

Evaluation of the use of microwave oven systems for the digestion of environmental samples

In most chemical analyses for inorganic determinations in environmental matrices the sample is physically destroyed by dissolution, calcination etc. These digestion procedures have to be validated in order to ensure that no contamination and/or losses have occurred which could affect the accuracy of the final results obtained; this validation can be made by using certified reference materials (CRMs).In the recent past, microwave digestion procedures have been developed and have been shown to offer the benefits of rapid sample preparation and reduced contamination risks; however, an incomplete dissolution was suspected in some cases, e.g. in interlaboratory exercises, for the analysis of organic matrices.The aim of this study was to test microwave digestion procedures for different environmental CRMs and to evaluate the suitability of these methods for the determination of some trace elements. The effects of chemical species (As, Hg and Se-species) on the total element recovery after digestion are discussed.     

Optimization of microwave digestion for mercury determination in marine biological samples by cold vapour atomic absorption spectrometry

Optimization of acid digestion method for mercury determination in marine biological samples (dolphin liver, fish and mussel tissues) using a closed vessel microwave sample preparation is presented. Five digestion procedures with different acid mixtures were investigated: the best results were obtained when the microwave-assisted digestion was based on sample dissolution with HNO3-H2SO4-K2Cr2O7 mixture. A comparison between microwave digestion and conventional reflux digestion shows there are considerable losses of mercury in the open digestion system. The microwave digestion method has been tested satisfactorily using two certified reference materials. Analytical results show a good agreement with certified values. The microwave digestion proved to be a reliable and rapid method for decomposition of biological samples in mercury determination.     

基于色谱-质谱联用的脂质分析样品前处理技术研究进展

脂质作为细胞膜和亚细胞膜的主要结构成分,在能量来源、细胞信号传导等多种生物学过程中发挥着重要作用。近年来,脂质分析受到越来越多的关注,其中色谱-质谱联用技术在脂质分析中占据主导地位。由于样品基质复杂,样品前处理有富集痕量物质和减少基质干扰的作用,成为脂质分析中的一个关键步骤。该文综述了近年来基于色谱-质谱联用技术的脂质分析中样品前处理技术的研究进展和应用,对各种样品前处理技术进行了阐述和总结。基于液相的萃取方法有液-液萃取和单一有机溶剂萃取。基于固相的萃取方法包括固相萃取和固相微萃取。场辅助萃取方法包括超临界流体萃取、加压流体萃取、微波辅助萃取和超声辅助萃取。此外,还介绍了在线联用样品前处理方法和用于活体分析的样品前处理方法。最后,对基于色谱-质谱联用的脂质分析样品前处理技术存在的问题及发展趋势进行了探讨。样品前处理技术的发展将提高脂质分析的灵敏度、选择性和分析速度。     

Advance in Microwave-assisted Digestion Techniques

Since 1975 when Abu-samra first reported the use of microwave as a heat source for wet digestion methods, sample preparation techniques have ushered in a new era. Using this technique, not only has the sample matrix been decomposed completely, but also digestion times have been dramatically reduced with other benefits such as little contamination, less reagent and sample usage, reduction in loss of volatile species and low blank values. In this paper, some developments in microwave-assisted digestion (MAD) are presented.     

亚胺类共价有机骨架材料在样品前处理中的应用

亚胺类共价有机骨架(I-COFs)是有机单体根据席夫碱(Schiff-base)反应原理缩合形成的一类新型多孔晶体有机材料.I-COFs具有骨架密度低、比表面积大、孔隙率高、单体种类丰富、孔径尺寸可控、结构可功能化、合成方法多样和物化稳定性好等优点.近年来,I-COFs已成为材料科学领域的研究前沿,并广泛用于气体吸附、...     

微波技术在催化剂制备中的应用

微波作为一种独特的加热手段在化学领域已得到广泛应用。本文综述了微波技术在催化剂的合成、活性组分的负载等方面的研究应用,重点探讨了在分子筛催化剂的合成中微波技术所表现出的优越性,对微波合成催化剂的作用机理及影响因素作了评述,并展望了微波技术在催化领域的发展前景。     

Microwave chemical processing

The chemical industry admits to minimal use of microwave power because of its high capital and operating costs relative to steam, combustion, electrical, and other traditional sources of energy. Other valid historical and persistent reasons for their lack of proper use include: a poor conceptual understanding of microwaves by chemical professionals, their unwillingness to replace existing adequate methods with radically new technology, the infancy of the microwave industrial power supply, and unfamiliarity of microwave power systems manufacturers with the chemical industry. In years past, the North American chemical industry had few competitors and profits were generally large. Environmental regulations were few and product quality was less a concern than production volume. The microwave power industry relied on the government and communications for lucrative sales. Those days appear over. Chemical manufacturers must probe every technology to achieve the edge necessary to stay competitive while meeting environmental stewardship demands. Microwave power has always offered unique advantages in heating materials selectively and/or quickly to high or preselected temperatures with fast control response. In the cases discussed in this paper, novel applications of microwave power afford: faster production, a reduction in product contaminants, reduced downtime, reduced waste, product quality improvements, and better pollution control.     

Rapid and Efficient Synthesis of Diaryl Carbazones using Microwave Technology

Diaryl carbazone is an important organic analytical reagent normally prepared by the oxidation of diaryl carbazine, but in literatures' methods, the yields were low and the procedures were trouble1,2. Recently, our laboratory reported some new methods for the preparation of diaryl carbazone from diaryl carbazine3,4. Generally, these methods have drawbacks such as tedious operation3, using large amounts of volatile and poisonous solvent which will pollute the environment inevitably3, long reaction time and complicated oxidation system4. In continuation of our studies on the synthesis of azo compounds, we decided to develop a new method to overcome the limitation.As we know, the application of microwave techniques for organic synthesis has attracted considerable interests in recent years5. Using microwave technology can enhance the selectivity and reactivity, increase the chemical yields and shorten the reaction time6. It has been widely used in a variety of organic reactions7,8. However, the synthesis of diaryl carbazones using microwave has not been reported so far.In this paper, a rapid and efficient synthesis of diaryl carbazones with NaBrO3/H2SO4 as oxidation system using microwave technology is reported for the first time. By this method, in short time (0.5 rmin), we have synthesized ten diaryl carbazones in good yields.In the oxidation study, we found that the acidic condition is necessary in these reactions.This method only needs cheap and easily available oxidants, simple instruments and easy work-up.In conclusion, It is a facile and rapid method for the preparation of diaryl carbazones from diaryl carbazines with NaBrO3/H2SO4.     

Microwave assisted extraction for mercury speciation analysis

The application of microwave-assisted extraction (MAE) to the work-up of environmental and biological samples in the study of mercury speciation analysis has increased in recent years and is now increasingly accepted as a standard approach. The review provides a brief theoretical background of microwave heating and the basic principles of microwave energy used for extraction. The advantages and disadvantages of (a) MAE techniques, (b) the influence of the main parameters affecting the extraction, (c) statistical optimization approaches, and (d) strategies for method validation also are highlighted. Recent applications of MAE to mercury species analyses in biological samples, soils, sediments, and crude oil samples are surveyed and critically reviewed. In addition, comparisons of its use with other well-established extraction procedures are discussed.

Sample preparation methods for subsequent determination of metals and non-metals in crude oil—A review

In this review sample preparation strategies used for crude oil digestion in last ten years are discussed focusing on further metals and non-metals determination. One of the main challenges of proposed methods has been to overcome the difficulty to bring crude oil samples into solution, which should be compatible with analytical techniques used for element determination. On this aspect, this review summarizes the sample preparation methods for metals and non metals determination in crude oil including those based on wet digestion, combustion, emulsification, extraction, sample dilution with organic solvents, among others. Conventional methods related to wet digestion with concentrated acids or combustion are also covered, with special emphasis to closed systems. Trends in sample digestion, such as microwave-assisted digestion using diluted acids combined with high-efficiency decomposition systems are discussed. On the other hand, strategies based on sample dilution in organic solvents and procedures recommended for speciation analysis are reported as well as the use of direct analysis in view of the recent importance for crude oil field. A compilation concerning sample preparation for crude oil provided by official methods as well as certified reference materials available for accuracy evaluation is also presented and discussed.     

微波场助光催化氧化及其应用

从半导体光催化机理、微波制备光催化剂和微波场助光催化反应等几个方面,简述微波在光催化领域中应用的研究现状和进展,探讨了微波-紫外光的耦合对提高光催化量子效率的作用.     

The progress of microwave-assisted hydrothermal method in the synthesis of functional nanomaterials

Developing simple, rapid, and environmentally friendly synthetic methodologies for the preparation of functional nanomaterials is of great importance for broadening and improving their potential applications. In comparison with other methods, the microwave-assisted hydrothermal method possesses and combines the merits of microwave and hydrothermal methods, which can achieve the high temperature and high pressure for a short time from several minutes to several hours in a closed reaction system. In this review, the synthesis of various types of functional nanomaterials such as metals oxides, metal composite oxides, inorganic biomaterials (hydroxyapatite and calcium carbonate), and metal sulfides via the microwave-assisted hydrothermal method is summarized. The special properties and applications of functional nanomaterials by the microwave-assisted hydrothermal method are compared with others methods. The future developments of this promising method are put forward.     

基于生命周期评价技术研究全铁含量测定对环境的影响

利用生命周期评价软件Sima Pro7和环境影响评价模型IMPACT 2002+,通过对化学分析方法的清单分析及计算,评价和比较了3种测定铁矿中全铁含量的化学分析方法(酸溶法、碱熔法、微波消解法)对人类健康、生态质量、气候变化及资源消耗等的影响。发现3个方法对环境的影响主要集中于人类健康危害、气候变化和资源消耗方面。通过计算3种方法的生命周期单一环境负荷值,发现碱熔法、酸溶法和微波消解法的单一环境负荷值分别为1.97,1.81,0.07 m Pt,对环境总体的影响,碱熔法和酸溶法分别为微波消解法的28倍和26倍。单独对人类健康危害指标而言,碱熔法为1.15 m Pt,酸溶法为1.07 m Pt,微波消解法仅为0.039 6 m Pt。碱熔法、酸溶法和微波消解法的碳足迹分别为5.12,4.62,0.189 kg CO_2eq。说明微波消解法排放量最小,其环境友好性最佳,值得推荐。     

Microwaves and chemistry: The catalysis of an exciting marriage

The potential of microwave power as a tool to facilitate chemical reactions has not whetted the chemist’s appetite in the past and the phenomenon and uses of microwaves have remained in the comer of spectroscopists and engineers for a long time. The possibility of microwaves initiating chemical changes has nevertheless excited our imagination for the past ten years. We will present the original development of the concept of microwave catalysis/sensitization in chemistry and the coming of age of the techniques as an enabling technology in the industrial world. A number of demonstrated applications ranging from hydrocarbon oxidations to environmental technology will be illustrated, as well as the most recently developed technique and applications of the microwave-induced acoustic phenomenon.     

Microwave assisted sample preparation for determining water-soluble fraction of trace elements in urban airborne particulate matter: evaluation of bioavailability

The feasibility of using two different microwave-based sample preparation methods was investigated to determine the total and water-soluble trace metal fraction in airborne particulate matter. The extraction techniques were then applied to urban particulate matter of different sizes in order to evaluate their bioavailability of associated trace metals. While a combination of HNO₃-HF-H₂O₂ was used for the total trace metal fraction of particulate matter, water was employed for the microwave-assisted extraction of water-soluble trace metal fractions. Inductively coupled plasma-mass spectrometry (ICP-MS) was used for the analysis of trace elements. The experimental protocol for the microwave assisted digestion was established using two different SRMs (1648, urban particulate matter and 1649a, urban dust). In the case of water-soluble trace metal fraction, the quantities extracted from the SRMs were compared between ultrasonic and microwave-assisted extractions, and there was a good agreement between the two extraction methods. Blanks values and limits of detection (LODs) for total and water-soluble trace metal concentrations were determined for three different filter substrates (Teflon, Zeflour, and Quartz). Subsequently, the proposed digestion method was evaluated for its extraction efficiency with these filter substrates. Finally, the real-world application of the proposed microwave-based sample preparation methods was demonstrated by analyzing trace elements in airborne particulate samples collected from different outdoor environments in Singapore. The solubility of 11 trace elements detected in the particulate samples is quantified.     

微波与有机化学反应的选择性

本文综述了微波辅助下有机化学反应的选择性,包括化学选择性、区域选择性、顺反选择性、非对映选择性、对映选择性,与传统加热条件下反应选择性的区别。讨论了微波对有机化学反应选择性的影响。从文献报道的结果来看,虽然观察到了一些反应在微波照射与加热条件下显示出不同的选择性,但绝大部分例子并不是在严格相同的条件下进行的对比,还有一些虽然做了对比研究,但却忽略了温度的影响。对于绝大多数例子,微波产生的选择性的差别似乎都可以用热效应来解释。可以认为微波辅助的反应中基本不存在特殊的"非热效应"。微波辅助技术可以通过改变反应温度来实现改变某些反应的选择性。希望本文对微波效应和微波对有机反应加速效应的本质的理解提供一些有用信息。     

Recent developments in sample preparation techniques for chromatography analysis of traditional Chinese medicines

Traditional Chinese medicines (TCMs) have a long history dating back thousands of years. Recently, there has been increasing interest worldwide in the use of TCMs for the prevention and treatment of various illnesses. In China, a large number of analytical tools, especially chromatographic techniques have been used to analyze the constituents of TCMs in order to control their quality and discover new bioactive compounds. In this paper, recent developments in sample preparation techniques for the extraction, clean-up, and concentration of analytes from TCMs are compared. These techniques include headspace solid-phase microextraction (HS-SPME), headspace liquid-phase microextraction (HS-LPME), microwave-assisted extraction (MAE), supercritical-fluid extraction (SFE), pressurized-liquid extraction (PLE), and microwave distillation (MD).     

Microwave activation as an alternative production of metal-organic frameworks

The review is devoted to analysis of the modern data concerning microwave-assisted synthesis of metal-organic frameworks (MOFs). The prospects for the microwave activation of the reaction mixture as an effective method of MOF formation with tuned crystallite size are considered. Other aspects of this approach including impact of various factors (reaction mixture composition, microwave synthesis parameters) on the texture properties and morphology of MOFs are discussed. Comparative studies concerning the influence of preparation methods in the microwave fields and other procedures of MOF fabrication on the physicochemical properties of the samples are considered. Advantages of microwave synthesis from green chemistry point are outlined.     

An advanced LC-MS (Q-TOF) technique for the detection of amino acids in atmospheric aerosols

Methodology for detection of native (underivatized) amino acids (AA) in atmospheric aerosols has been developed. This article describes the use of LC-MS (Q-TOF) and microwave-assisted gas phase hydrolysis for detection of free and combined amino acids in aerosols collected in a Southeastern U.S. forest environment. Accurate mass detection and the addition of isotopically labeled surrogates prior to sample preparation allows for sensitive quantitation of target AA in a complex aerosol matrix. A total of 16 native AA were detected above the reporting threshold as water-soluble free AA, with an average concentration of 22 ± 9 ng m⁻³ (N = 13). Following microwave-assisted gas phase hydrolysis, the total AA concentration in the forest environment increased significantly (70 ± 35 ng m⁻³) and additional compounds (methionine, isoleucine) were detected above the reporting threshold. The ability to quantify AA in aerosol samples without derivatization reduces time-consuming preparation procedures while providing the advancement of selective mass determination for important organic nitrogen (ON) species. Details on sample preparation that eliminates the freeze-drying approach typically practiced for water removal with biological samples, and vapor phase microwave hydrolysis parameters are provided. Method application for determination of atmospheric ON is discussed.