Microwave assisted methodology for the determination of organic pollutants in organic municipal wastes and soils: extraction of polychlorinated biphenyls using heat transformer disks

Known benefits of microwave assisted extraction (MAE) of polychlorinated biphenyls (PCB) from solid matrices could be proven by the described approach using n-heptane as solely applied extraction solvent. Heat transfer within the extraction vessels was achieved by heat transformer disks which absorb microwave energy and transform it into heat rapidly and independently of the temperature present in the sample-solvent system. Disadvantageous co-extraction of polar substances could be ruled out and thus clean-up of the samples was simplified and sufficient for subsequent GC-MS analysis. Comparison with other extraction techniques confirmed the efficiency of this method also for aged samples.     

微波吸收介质管-微波辅助提取水果中的有机磷农药

使用自行设计的微波吸收介质管辅助加热样品, 建立了一种新的微波加速提取法, 并以正己烷为提取溶剂, 利用改装的便携式微波提取仪提取了水果中的4种有机磷农药. 将微波介质密封于玻璃管内制成微波介质管, 使微波介质可重复使用, 同时加快了提取速度. 提取产物无需纯化, 可直接用于气相色谱-质谱联用(GC-MS)分析. 自行设计改装的交直流两用便携式微波提取仪可用于野外现场的快速样品前处理. 以水果样品为例, 对提取溶剂的种类、 料液比、 提取温度及提取时间等条件进行了优化, 结果表明该方法简便、 快速且高效. 4种有机磷农药的回收率为79.4% ~107.6%, RSD<12.20%, 检出限为0.15 ~0.42 μg/kg.     

Comparison of microwave-assisted extraction of triazines from soils using water and organic solvents as the extractants

Microwave-assisted extraction (MAE) for the separation of atrazine, simazine and prometryne from synthetic soil samples, using water and some organic solvents as the extractants, was studied in detail. The effects of the soil matrix, the soil moisture and the pH of the aqueous extraction system on the MAE efficiency were also studied. It was found that the three triazines could be efficiently extracted under the conditions of 100% magnetron power output (600 W), the first grade of pressure (from 0.1 MPa to 0.5 MPa), 30 ml solvent and 4 min microwave heating with water or organic solvents, except for prometryne with dichloromethane solvent for 1-4 g sandy loam sample. This interesting result was explained by triazines' solubility in water, their sorption properties in soils and the ability of the solvent to absorb microwave energy. Finally, evaluation of the extraction efficiency, as well as the treatment and determination of MAE extracts, suggested that water, as a cheap, safe and environmentally friendly solvent, can be a good alternative to organic solvents, used as the extractants for MAE of triazines from soils.     

Analysis of emerging organic contaminants in environmental solid samples

Spreading sewage sludge on agricultural lands has been actively promoted by national authorities as an economic way of recycling. However, as by-product of wastewater treatment, sewage sludge may contain toxic substances, which could be incorporated into agricultural products or be distributed in the environment. Moreover, sediments can be contaminated by the discharge of wastewater effluents into rivers. This article reviews the determination of emerging contaminants (surfactants, flame retardants, pharmaceuticals and personal care products) in environmental solid samples (sludge, soil and sediment). Sample preparation, including extraction and clean-up, as well as the subsequent instrumental determination of contaminants are discussed. Recent applications of extraction techniques, such as Soxhlet extraction, ultrasound assisted extraction, pressurised liquid extraction, microwave assisted extraction and matrix solid-phase dispersion to the analysis of emerging contaminants in environmental solid samples are reviewed. Determination of these contaminants, generally carried out by gas chromatography and liquid chromatography coupled with different detectors, especially mass spectrometry for the identification and quantification of residues, is also summarised and discussed.      

High-throughput dynamic microwave-assisted extraction on-line coupled with solid-phase extraction for analysis of nicotine in mushroom

A simple and low-cost high-throughput dynamic microwave-assisted extraction (HTDMAE) device was firstly assembled and validated by the extraction of nicotine in mushroom samples. In this device, a household microwave oven was applied to provide the microwave energy; a vacuum pump was used to deliver the solvent. Compared with traditional dynamic microwave-assisted extraction method, the sample throughput and microwave energy utilization were improved by the HTDMAE, up to 20 samples could be treated simultaneously in 9 min. Taking extraction of nicotine in mushroom sample as an example, a method was established with extraction, separation and enrichment of nicotine in a single step by the device on-line coupled with solid-phase extraction (SPE). Nicotine was first extracted from the mushroom samples with water under the action of microwave energy, and then directly introduced into the SPE column which was packed with cation-exchange resins. Subsequently, the nicotine trapped on the resins was eluted with methanol-ammonia (95:5, v/v) and determined by high-performance liquid chromatography. The limit of detection of nicotine obtained is 5.6 μg kg(-1) in fresh mushroom sample. The recovery of nicotine in mushroom samples is in the range of 87.4-104.0%. The proposed method which significantly reduced the overall analysis time and increased sample throughput should be favored for routine analyse of complex solid sample.     

Controlled microwave heating in modern organic synthesis

Although fire is now rarely used in synthetic chemistry, it was not until Robert Bunsen invented the burner in 1855 that the energy from this heat source could be applied to a reaction vessel in a focused manner. The Bunsen burner was later superseded by the isomantle, oil bath, or hot plate as a source for applying heat to a chemical reaction. In the past few years, heating and driving chemical reactions by microwave energy has been an increasingly popular theme in the scientific community. This nonclassical heating technique is slowly moving from a laboratory curiosity to an established technique that is heavily used in both academia and industry. The efficiency of "microwave flash heating" in dramatically reducing reaction times (from days and hours to minutes and seconds) is just one of the many advantages. This Review highlights recent applications of controlled microwave heating in modern organic synthesis, and discusses some of the underlying phenomena and issues involved.     

Analytical-scale microwave-assisted extraction

Microwave-assisted extraction (MAE) is a process of using microwave energy to heat solvents in contact with a sample in order to partition analytes from the sample matrix into the solvent. The ability to rapidly heat the sample solvent mixture is inherent to MAE and the main advantage of this technique. By using closed vessels the extraction can be performed at elevated temperatures accelerating the mass transfer of target compounds from the sample matrix. A typical extraction procedure takes 15-30 min and uses small solvent volumes in the range of 10-30 ml. These volumes are about 10 times smaller than volumes used by conventional extraction techniques. In addition, sample throughput is increased as several samples can be extracted simultaneously. In most cases recoveries of analytes and reproducibility are improved compared to conventional techniques, as shown in several applications. This review gives a brief theoretical background of microwave heating and the basic principles of using microwave energy for extraction. It also attempts to summarize all studies performed on closed-vessel MAE until now. The influences of parameters such as solvent choice, solvent volume, temperature, time and matrix characteristics (including water content) are discussed.     

Extraction of pesticides from sediments using a microwave technique

Summary The microwave energy produced by high intensity microwave oven, was used to extract pesticides from sediment samples. This system was compared with Soxhlet, sonification and convection heat extraction techniques. Sediment moisture and type of organic matter content are critical parameters in affecting the degree of recovery. Extraction procedure using a 30 second period repeated in sequence 5 times provided generally better recovery values than did 8 hours of Soxhlet extraction.     

Non-polar Solvent Microwave-Assisted Extraction of Volatile Constituents from Dried Zingiber Officinale Rosc.

A new method, non-polar solvent microwave-assisted extraction （NPSMAE）, was applied to the extraction of essential oil from Zingiber officinale Rosc. in closed-vessel system. By adding microwave absorption mediumcarbonyl iron powders （CIP） into extraction system, the essential oil was extracted by the non-polar solvent （ether） which can be heated by CIP. The constituents of essential oil obtained by NPSMAE were comparable with those obtained by hydrodistillation （HD） by GC-MS analysis, which indicates that NPSMAE is a feasible way to extract essential oil from dried plant materials. The NPSMAE took much less extraction time （5 min） than HD （180 min）, and its extraction efficiency was much higher than that of conventional polar solvent microwave-assisted extraction （PSMAE） and mixed solvent microwave-assisted extraction （MSMAE）. It can be a good alternative for the extraction of volatile constituents from dried plant samples.     

Comparison of single extraction procedures,using either conventional shaking or microwave heating,and the Tessier sequential extraction method for the fractionation of heavy metals from environmental samples

The conventional four-step sequential extraction method and the EDTA and acetic acid single extraction procedures were applied to sewage sludge and sediment samples. The results obtained with these samples for Cu, Cr, Ni, Pb and Zn using the Tessier method were compared with those supplied by the two single extraction procedures employed. In addition, the Tessier method was also applied to a reference material, CRM 483, and these results were also compared with the certified EDTA and acetic acid values for this sample. As a result, good agreement was found between the metal contents released in the first three fractions of the Tessier method and those leached by the simpler single extraction procedures for the most of the elements studied. Subsequently, the conventional EDTA and acetic acid extraction methods were accelerated by means of microwave energy, in order to reduce the operating time. The extraction efficiency of the first three fractions of the Tessier method was compared with that obtained using the optimised microwave single extraction procedures and only in sewage sludge and CRM 483 samples were satisfactory results found for all the elements studied, except Cr and Pb. This means that the microwave single extraction procedures optimised in this work could be employed as screening methods to evaluate rapidly the easiest mobilizable heavy metals in these samples, although more samples should be analysed to determine their general applicability. The application of the accelerated single extraction procedures to a reference material, CRM 483, provided satisfactory results for all the elements studied, except for Cr in both methods and for Pb in the acetic acid extracts.     

Microwave-assisted double insert vapour-phase digestion of organic samples

A microwave-assisted double insert multimode vapour-phase digestion method was developed for the digestion of organic samples. The experimental set-up was based on a third generation-type teflon microwave vessel, equipped with an automatic pressure regulating type vessel cover. A borosilicate glass holder insert, containing a smaller quartz sample insert, was fitted inside the vessel. Sulphuric acid was added to the holder insert as a microwave absorbing and temperature transferring liquid, which transferred heat to the sample insert (into which the sample was weighed) and charred the sample material. Oxidation of the sample material was carried out simultaneously with charring using nitric acid vapour, which was generated by the 1:1 (v/v) sulphuric acid-nitric acid mixture located in the bottom of the microwave vessel. This set-up generated high digestion efficiency, without any of the interferences normally associated with direct sulphuric acid usage. The method was used for determining the concentrations of Cd, Cr, Cu, Mn, Mo, Zn and Fe in certified organic reference materials using ICP-OES instrumentation. The certified organic reference materials were NRCC DOLT-2 dogfish liver, NIST-SRM 1577b bovine liver and IRMM VDA cadmium in polyethylene No. 001 and No. 004. The results were in good agreement with the certified values, forepart from Cd. For Cd the results were lower than the certified values due to volatilization losses. Sample materials that could not be digested by an earlier procedure were completely digested during a single-step, 30 min digestion. The tested sample materials included certified reference materials, 3-nitrobenzoic acid (3-NBA) and pike (Esox lucius) muscle. The residual carbon concentrations in the digestion solutions were below the detection limit of the TOC instrument. This type of digestion method is described here for the first time in the literature.     

Analysis of organic compounds of water-in-crude oil emulsions separated by microwave heating using comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry

In this work the higher peak capacity and resolution of comprehensive two-dimensional gas chromatography (GCxGC) has been successfully applied, for the first time, to tentatively identify several polar organic compounds of organic extracts of aqueous phases resulting from microwave demulsification process of water-in-crude oil emulsions. Results have shown that higher temperatures and longer exposure time to microwave irradiation produced water phases with a wider variety of polar organic compounds. The microwave process showed to be suitable for the extraction of several polar compounds classes of petroleum. The proposed microwave extraction method and GCxGC identification of polar compounds of petroleum samples are of practical interest for the petrochemical industry due to corrosion and related problems associated with these polar compounds in refinery equipments. The GCxGC/time-of-flight MS technique shows to be very important in the total separation of different classes of compounds and allows the identification of many compounds in these classes.     

Ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction and derivatization of sulfonamides in river water, honey, milk, and animal plasma

The ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction (IL-based MADLLME) and derivatization was applied for the pretreatment of six sulfonamides (SAs) prior to the determination by high-performance liquid chromatography (HPLC). By adding methanol (disperser), fluorescamine solution (derivatization reagent) and ionic liquid (extraction solvent) into sample, extraction, derivatization, and preconcentration were continuously performed. Several experimental parameters, such as the type and volume of extraction solvent, the type and volume of disperser, amount of derivatization reagent, microwave power, microwave irradiation time, pH of sample solution, and ionic strength were investigated and optimized. When the microwave power was 240 W, the analytes could be derivatized and extracted simultaneously within 90 s. The proposed method was applied to the analysis of river water, honey, milk, and pig plasma samples, and the recoveries of analytes obtained were in the range of 95.0-110.8, 95.4-106.3, 95.0-108.3, and 95.7-107.7, respectively. The relative standard deviations varied between 1.5% and 7.3% (n=5). The results showed that the proposed method was a rapid, convenient and feasible method for the determination of SAs in liquid samples.     

Microwave-assisted steam distillation with simultaneous liquid/liquid extraction of pentachlorophenol from organic wastes and soils

An efficient method for extracting pentachlorophenol (PCP) from organic solid matrices and soils using direct excitation of the fresh samples by microwave energy is presented. Steam-volatile PCP partitioned into the organic solvent n-hexane within the closed extraction vessel, resulting in recovery rates of 85-92% from aged samples. Condensed water provided a boundary layer between extract and sample thus preventing any contact of PCP with and re-partitioning into the sample. Duration of the microwave-assisted process was 35 min. Crude extracts were derivatized by heptafluorobutyric anhydride (HFBA) to improve selectivity and sensitivity resulting in detection limits of 1-2 micro g kg(-1). GC-MS/MS analyses proved that suitable extracts with only minor impurities were obtained. Common sample treatment steps like drying, thorough grinding, frequent transferring, and tedious clean-up, and concentration procedures which all can cause certain losses of analyte were minimized. The efficiency of the method was verified by comparison with an established ultrasonic extraction procedure. This microwave-assisted pressurized steam distillation with simultaneous partition into an organic phase thus provides a streamlined and efficient strategy which requires no additional investment in standard equipment for microwave-assisted extractions (MAE). Degradation of analytes at longer extraction times must be taken into account.     

Analysis of semi-volatile organic compounds in aqueous samples by microwave-assisted headspace solid-phase microextraction coupled with gas chromatography-electron capture detection

The pretreatment technique of microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) has been developed and studied for the extraction of semi-volatile organic compounds (SVOCs) in aqueous samples prior to chromatographic analysis. The optimum conditions for obtaining extraction efficiency, such as the extraction time, extraction temperature, addition of salts, and the ratio of sample to headspace volume parameters were investigated. Experimental results indicated that the proposed MA-HS-SPME technique attained the best extraction efficiency under the optimized conditions, i.e., irradiation of extraction solution (20mL aqueous sample in 40mL headspace vial with no addition of salt) under 30W microwave power for 30min at 70 degrees C. The detection was linear at 1-250ng/L with correlation coefficient exceeding 0.997. The detection limits obtained were between 0.2-10.7ng/L, repeatability range from 2 to 15%. Real water samples collected from known sites in southern Taiwan were analyzed using the optimized conditions.     

Design of guanidinium ionic liquid based microwave‐assisted extraction for the efficient extraction of Praeruptorin A from Radix peucedani

A series of novel tetramethylguanidinium ionic liquids and hexaalkylguanidinium ionic liquids have been synthesized based on 1,1,3,3‐tetramethylguanidine. The structures of the ionic liquids were confirmed by ¹H NMR spectroscopy and mass spectrometry. A green guanidinium ionic liquid based microwave‐assisted extraction method has been developed with these guanidinium ionic liquids for the effective extraction of Praeruptorin A from Radix peucedani. After extraction, reversed‐phase high‐performance liquid chromatography with UV detection was employed for the analysis of Praeruptorin A. Several significant operating parameters were systematically optimized by single‐factor and L₉ (3⁴) orthogonal array experiments. The amount of Praeruptorin A extracted by [1,1,3,3‐tetramethylguanidine]CH₂CH(OH)COOH is the highest, reaching 11.05 ± 0.13 mg/g. Guanidinium ionic liquid based microwave‐assisted extraction presents unique advantages in Praeruptorin A extraction compared with guanidinium ionic liquid based maceration extraction, guanidinium ionic liquid based heat reflux extraction and guanidinium ionic liquid based ultrasound‐assisted extraction. The precision, stability, and repeatability of the process were investigated. The mechanisms of guanidinium ionic liquid based microwave‐assisted extraction were researched by scanning electron microscopy and IR spectroscopy. All the results show that guanidinium ionic liquid based microwave‐assisted extraction has a huge potential in the extraction of bioactive compounds from complex samples.     

Effect of sample handling on alkaloid and mineral content of aqueous extracts of greater celandine (Chelidonium majus L.)

The authors examined the extraction of alkaloids from the greater celandine (Chelidonium majus L.) by different methods (traditional pressing and tea making, microwave and supercritical fluid extraction). The extractants were water and propylene glycol. For comparison of the extraction methods, the yield was evaluated according to total alkaloid content measured by spectroscopy. The highest alkaloid yield was obtained by microwave extraction and by making tea. Distribution of the components was studied by thin-layer chromatography and densitometry. The concentration and the ratio of alkaloid components in extracts are significantly different depending on the extraction method. The solution obtained by supercritical fluid extraction contains coptisine and chelidonine, while berberine could be obtained by microwave extraction only. Extracts with high coptisine content were obtained by supercritical fluid extraction, followed by pressing and microwave extraction. Mineral element content of the drug and extracts was also determined by inductively coupled plasma atomic emission spectrometry. Element content (Na, Ca, Fe) was found to be highest in microwave extracts.     

微波酸提取/液相色谱-电感耦合等离子体质谱法测定动物源性中药中6种砷形态

建立了微波酸提取/液相色谱-电感耦合等离子体质谱联用(LC-ICP-MS)测定动物源性中药中6种砷形态(亚砷酸盐As(Ⅲ),砷酸盐As(V),一甲基砷MMA,二甲基砷DMA,砷甜菜碱As B和砷胆碱As C)的分析方法。采用1%HNO_3溶液在80℃微波提取10 min,经离心分层,过固相萃取SEP C18柱和0.45μm滤膜,以25 mmol/L NH_4H_2PO_4溶液(p H 6.7)-乙醇(99∶1,体积比)为流动相进行等度洗脱,各砷形态在10 min内实现基线分离。结果显示,6种砷形态在1.0~100.0μg/L范围内线性关系良好,相关系数为0.999 5~0.999 7,方法检出限(LOD)为0.24~1.0μg/kg,相对标准偏差(RSD)为0.96%~2.0%。将方法应用于地龙、水蛭、海螵蛸、桑螵蛸、石决明和鸡内金中6种砷形态的测定,加标回收率为94.2%~103.8%,提取效率为95.5%~102.8%,优于热提取法。方法快速、准确、重现性好,适用于动物源性中药及类似样品中的砷元素形态分析及质量监控。     

超声微波协同萃取/气相色谱法测定土壤中的多溴联苯醚

建立了同时测定土壤中7种多溴联苯醚(PBDEs)的超声微波协同萃取/气相色谱测定方法.考察了萃取溶剂的种类和用量、微波功率、萃取时间等因素对模拟土壤中PBDEs回收率的影响,得到了最佳萃取条件:萃取剂为50 mL正己烷-丙酮(1:1),微波辐射功率为90W,萃取时间为10 min.在最佳条件下,PB-DEs在10～40...     

Determination of ergosterol on mouldy building materials using isotope dilution and gas chromatography-tandem mass spectrometry

Ergosterol content of building materials was quantified using gas chromatography-tandem mass spectrometry (GC-MS-MS) in an ion trap with external ionisation. Hydrolysing the samples by classic extraction at 85 degrees C for 90 min in vials was faster, more precise and safer than microwave assisted extraction. [4-2H2]ergosterol was synthesised and used as internal standard, giving method standard deviation of 5-10% from 10 to 30 ng to 10-15 microg ergosterol in the sample. The use of GC-MS-MS meant that no solid-phase extraction clean-up was needed, so one person could easily prepare 40-80 samples per day.