Microwave-assisted extraction of polycyclic aromatic compounds from coal

Microwave-assisted extraction (MAE) of polycyclic aromatic compounds (PACs) from coal is shown to give the same pattern of compounds as Soxhlet extraction. MAE requires only 10 mL solvent and 10 min extraction time whereas Soxhlet uses 200 mL and takes 24 h. Although the yields were lower, dichloromethane (DCM) was preferred to pyridine, N-methyl-2-pyrrolidone (NMP), and NMP with CS2 because the pattern of the PACs is shown to be independent of solvent and DCM is a much more convenient solvent to work with.     

溶剂萃取预处理对低阶煤大分子结构的影响

为了研究溶剂预处理对低阶煤的固有大分子结构的影响,本研究对锡林郭勒褐煤（XLL）和神府次烟煤（SFC）分别进行了四氢呋喃（THF）索氏抽提、二硫化碳/N-甲基-2-吡咯烷酮（CS₂/NMP）混合溶剂抽提及热溶处理,并对所得抽余煤进行了傅里叶红外漫反射光谱分析（DRIFT）、热重分析（TGA）、压汞法分析（MI）和溶胀度测定。结果表明,溶剂抽提导致煤大分子结构重排和再缔合。其中,THF索式抽提和CS₂/NMP混合溶剂抽提可以改变非共价键交联作用,特别是氢键作用分布,从而不同程度地松弛煤大分子结构。然而,高温溶剂热溶处理主要促进了煤大分子的共价键交联,尤其是对锡林郭勒褐煤（XLL）。所有抽取煤的溶胀都受Fickian扩散控制,且所有抽取煤的溶胀活化能都低于原煤。     

Multiple response optimisation based on desirability functions of a microwave-assisted extraction method for the simultaneous determination of chloroanisoles and chlorophenols in oak barrel sawdust

A microwave-assisted extraction (MAE) method was optimised for extracting 2,4,6-trichloroanisole (TCA), 2,3,4,6-tetrachloroanisole (TeCA), pentachloroanisole (PCA), 2,4,6-trichlorophenol (TCP), 2,3,4,6-tetrachlorophenol (TeCP) and pentachlorophenol (PCP) from oak barrels. The method was optimised by using a central composite experimental design with extraction time, temperature and solvent volume as influential parameters. A desirability function was then employed in addition to the simultaneous optimisation of the compounds. The optimal conditions identified were temperature 130 degrees C, solvent volume 35 mL and extraction time 50 min. The compounds were determined by gas chromatography with electron-capture detection. MAE was compared with conventional Soxhlet extraction; the results obtained with MAE were in good agreement with those obtained by Soxhlet extraction.     

Determination of phthalate esters content in plastic articles: Comparison of extraction methods

Two variants of solvent extraction method (by Soxhlet and ultrasonic) for phthalate esters (DEHP) recoveries in PVC samples were compared. Solvent and extraction time for both techniques were also studied. DEHP content was quantified by GC-MS. The results obtained were compared using statistical methods (LSD test, t-test). 16-Hours DCM Soxhlet and 2-h DCM ultrasonic extraction methods were more convenient with respect to recovery, precision and practicability.     

Optimisation of focused ultrasound extraction (FUSE) and microwave-assisted extraction (MAE) of hydrocarbons in geological chert samples

The analysis of hydrocarbons in chert rocks provides a worthwhile source of information regarding the geochemical features of a depositional setting. Since the typical analytical procedure requires long Soxhlet extractions and the use of large quantities of sample (30-50 g), in this work we have optimised the focused ultrasound extraction (FUSE) and the microwave-assisted extraction (MAE) to make available a less severe procedure. In both cases a full experimental design including solvent mixture composition (Dichloromethane/Hexane/Acetone) and process variables (sonication time and cycles, and extraction temperature and time) by means of D-optimal designs. In the extracted fractions hydrocarbons (C₁₆-C₄₀) were analysed by gas-chromatography-mass spectrometry. In the case of FUSE the process variables were the most sensitive variables and the optimum conditions were defined at 60:40 DCM/Hex mixture and a sonication time of 30 min and 9 cycles. In the case of MAE all the variables shown a significant effect on the extraction yield and the most adequate conditions (60:30:10 DCM/Hex/Ace mixture and an irradiation time of 15 min at 110 °C) were established from the analysis of the response surface. Both methods were systematically applied with different chert samples collected in Cucho (Trebiño County, Burgos, Spain) and we were able to assure quantitative extractions (>85%) in the first extraction. Additionally, from the distribution patterns of n-alkanes obtained in the different chert samples (nodular chert, laminar chert and massive-brechoid chert) collected in Cucho, we were able to distinguish different origins and diagenetic history.     

Evaluation of Soxhlet extraction, accelerated solvent extraction and microwave-assisted extraction for the determination of polychlorinated biphenyls and polybrominated diphenyl ethers in soil and fish samples

Three commonly applied extraction techniques for persistent organic chemicals, Soxhlet extraction (SE), accelerated solvent extraction (ASE) and microwave-assisted extraction (MAE), were applied on soil and fish samples in order to evaluate their performances. For both PCBs and PBDEs, the two more recent developed techniques (ASE and MAE) were in general capable of producing comparable extraction results as the classical SE, and even higher extraction recoveries were obtained for some PCB congeners with large octanol-water partitioning coefficients (K_ow). This relatively uniform extraction results from ASE and MAE indicated that elevated temperature and pressure are favorable to the efficient extraction of PCBs from the solid matrices. For PBDEs, difference between the results from MAE and ASE (or SE) suggests that the MAE extraction condition needs to be carefully optimized according to the characteristics of the matrix and analyte to avoid degradation of higher brominated BDE congeners and improve the extraction yields.     

Improved sample treatment for the determination of insoluble soap in sewage sludge samples by liquid chromatography with fluorescence detection

A new selective and sensitive method for the determination of insoluble fatty acid salts (soap) in sewage sludge samples is proposed. The method involves a clean up of sample with petroleum ether, the conversion of calcium and magnesium insoluble salts into soluble potassium salts, potassium salts extraction with methanol, and a derivatization procedure previous to the liquid chromatography with fluorescence detection (LC-FLD) analysis. Three different extraction techniques (Soxhlet, microwave-assisted extraction and ultrasounds) were compared and microwave-assisted extraction (MAE) was selected as appropriate for our purpose. This allowed to reduce the extraction time and solvent waste (50 mL of methanol in contrast with 250 mL for Soxhlet procedure). The absence of matrix effect was demonstrated with two standards (C_13:0 and C_17:0) that are not commercials and neither of them has been detected in sewage sludge samples. Therefore, it was possible to evaluate the matrix effect since both standards have similar environmental behaviour (adsorption and precipitation) to commercial soaps (C_10:0-C_18:0). The method was successfully applied to samples from different sources and consequently, with different composition.     

Impact of Eutectic Solvents Utilization in the Microwave Assisted Extraction of Proanthocyanidins from Grape Pomace

The extraction of proanthocyanidins (PACs), despite being an important and limiting aspect of their industrial application, is still largely unexplored. Herein, the possibility of combining eutectic solvents (ESs) with microwave assisted extraction (MAE) in the extraction of PACs from grape pomace (GP) is explored, aiming to improve not only the extraction yield but also the mean degree of polymerization (mDP). The combination of choline chloride with lactic acid was shown to be the most effective combination for PACs extraction yield (135 mg_PAC/g_GP) and, despite the occurrence of some depolymerization, also enabled us to achieve the highest mDP (7.13). Additionally, the combination with MAE enabled the process to be completed in 3.56 min, resulting in a considerably reduced extraction time.     

Effects of Extraction Methods on Phenolic Content in the Young Bamboo Culm Extracts of Bambusa beecheyana Munro

Nowadays, many studies focus on the potential of bamboo as a source of bioactive compounds and natural antioxidants for nutraceutical, pharmaceutical, and food sources. This study is a pioneering effort to determine the total phenolic content, total flavonoid content and free radical scavenging activity, as well as the phenolic identification and quantification of Bambusa beecheyana. The study was conducted by using ethanol, methanol, and water for solvent extraction by applying cold maceration, Soxhlet, and ultrasonic-assisted extraction techniques. The results showed that Soxhlet and ultrasonic-assisted Bambusa beecheyana culm extracts had an increase in the extract’s dry yield (1.13–8.81%) but a constant p-coumaric acid (4) content (0.00035 mg/g) as compared to the extracts from the cold maceration. The ultrasonic-assisted extraction method required only a small amount (250 mL) of solvent to extract the bamboo culms. A significant amount of total phenolics (107.65 ± 0.01 mg GAE/g) and flavonoids (43.89 ± 0.05 mg QE/g) were found in the Soxhlet methanol culm extract. The extract also possessed the most potent antioxidant activity with an IC₅₀ value of 40.43 µg/mL as compared to the positive control, ascorbic acid. The UHPLC–ESI–MS/MS analysis was carried out on the Soxhlet methanol extract, ultrasonic-assisted extract at 40 min, and cold methanol extract. The analysis resulted in the putative identification of a total of five phenolics containing cinnamic acid derivatives. The two cinnamic acid derivatives, p-coumaric acid (4) and 4-methoxycinnamic acid (5), were then used as markers to quantify the concentration of both compounds in all the extracts. Both compounds were not found in the water extracts. These results revealed that the extract from Soxhlet methanol of Bambusa beecheyana could be a potential botanical source of natural antioxidants. This study provides an important chemical composition database for further preclinical research on Bambusa beecheyana.     

A rapid method for simultaneous determination of 14 phenolic compounds in Radix Puerariae using microwave-assisted extraction and ultra high performance liquid chromatography coupled with diode array detection and time-of-flight mass spectrometry

A microwave-assisted extraction (MAE) and ultra high performance liquid chromatography coupled with diode array detection and time-of-flight mass spectrometry (UHPLC-DAD-TOF-MS) method was developed for simultaneous determination of 14 phenolic compounds in the root of Pueraria lobata (Wild.) Ohwi and Pueraria thomsonii Benth. Operational conditions of MAE were optimized by central composite design (CCD). The optimized result was 65% ethanol as extraction solvent, 17 mL of extraction volume, 100 °C of extraction temperature and 2 min of hold time. A Zorbax SB C₁₈ (50 mm × 4.6 mm I.D., 1.8 μm) and gradient elution were used during the analysis. The chromatographic peaks of 14 investigated compounds in samples were successfully identified by comparing their retention time, UV spectra and TOF mass data with the reference substances. All calibration curves showed good linearity (r > 0.9997) within the test ranges. The intra-day and inter-day variations were less than 1.77% and 2.88%, respectively. The developed method was successfully applied to determine the investigated compounds in 10 samples of Radix Puerariae Lobatae and Radix Puerariae Thomsonii, respectively. The result indicated that MAE and UHPLC-DAD-TOF-MS system might provide a rapid method for the quality control of Radix Puerariae.     

Pressurised fluid extraction of polycyclic aromatic hydrocarbons and their polar oxidation products from atmospheric particles

An effective method utilising pressurised fluid extraction (PFE) to simultaneously extract polycyclic aromatic hydrocarbons (PAHs) and their polar oxidation products from atmospheric particulate matter (PM) is presented. The PFE method is advantageous over the traditional Soxhlet extraction due to its lower solvent consumption (9 mL compared to 90 mL) and shorter extraction time (15 min versus 18 h). Seventy compounds including PAHs and polar PAH oxidation products containing carbonyl (oxy-PAHs), hydroxyl (hydroxy-PAHs), and carboxylic acid (carboxy-PAHs) groups were targeted in the extraction of two different PM matrices: wood smoke (WS) and diesel exhaust (DE) PM. The PFE method was optimised and then compared to Soxhlet extraction for both PM matrices. The overall amounts of PAHs and their derivatives extracted from WS PM were slightly higher for the optimised PFE method (1849 ± 21 and 1863 ± 25 µg g^?1 with dichloromethane (DCM) and methanol (MeOH), respectively) than those obtained with Soxhlet extraction (1726 ± 33 and 1769 ± 22 µg g^?1 with DCM and MeOH, respectively). For DE PM (standard reference material (SRM) 2975) the overall amounts extracted by both methods were similar (average of 165 ± 6 µg g^?1), agreeing with previously published values. The detailed evaluation of extraction efficiencies for WS PM showed similar amounts for unfunctionalised PAHs (1100 µg g^?1) for both methods and solvents. For DE PM the mass yields for PAHs using PFE with DCM (62 ± 1 µg g^?1) were the highest and nearly 20% higher than those obtained with MeOH (53 ± 2 µg g^?1). The total mass yields of carboxy and hydroxy-PAHs from WS PM were also similar (412 ± 18 and 407 ± 11 µg g^?1) for PFE and Soxhlet with MeOH, and higher than when DCM was used (371 ± 5 and 379 ± 12 µg g^?1 for PFE and Soxhlet, respectively). For both matrices, the PFE yields for oxy-PAHs were higher than those obtained with Soxhlet.     

SPE – Microwave‐assisted extraction coupled system for the extraction of pesticides from water samples

SPE is a commonly applied technique for preconcentration of pesticides from water samples. Microwave‐assisted extraction (MAE) technique is the extraction applied for preconcentration of different compounds from solid samples. SPE coupled with MAE is capable of preconcentrating these compounds from water samples too. This investigation was aimed at improving the efficiency of atrazine, alachlor, and α‐cypermethrin pesticide extraction from the spiked water samples applying SPE followed by MAE. In this way, MAE served for elution of pesticides from C₁₈‐extraction disks with solvent heated by microwave energy. Various elution conditions were tested for their effects on the extraction efficiency of the SPE–MAE combined technique. Several parameters, such as elution solvent volume (mL), elution temperature (°C), and duration of elution (min), affect the extraction efficiency of the SPE–MAE coupled system and need to be optimized for the selected pesticides. In order to develop a mathematical model, 15 experiments were performed in the central composite design. The equation was then used to predict recoveries of the pesticides under specific experimental conditions. Optimization of microwave extraction was accomplished using the genetic algorithm approach. Best results were achieved using 20 mL of ethanol at 60°C. Optimal hold time was 5 min and 24 s. The SPE–MAE combination was also compared with the conventional SPE extraction technique with elution of a nonpolar or a moderately polar compound with nonpolar solvents.     

Kinetic Study on Chlorophyll and Antioxidant Activity from Polyscias fruticosa (L.) Harms Leaves via Microwave-Assisted Extraction

Polyscias fruticosa (L.) leaves contain significant bioactive compounds with high antioxidant activity such as chlorophylls, total polyphenols, etc. but these have still been underutilized. In this study, the kinetics of chlorophyll and antioxidant activity extraction from P. fruticosa leaves by microwave-assisted extraction (MAE) were investigated. Microwave power was 300, 450, or 600 (W); the ratio of material/solvent varied from 1:40 to 1:80 (g/mL). In this study, the second-order kinetic model successfully predicted the change of chlorophyll and antioxidant activity during MAE. The increase of microwave power or/and the solvent amount increased saturated extraction efficiency and the extraction rate constant. However, the saturated concentration of chlorophyll and antioxidant activity increased with the increment of microwave power and the decrease in solvent amount.     

Comparison of different extraction techniques for the determination of chlorinated pesticides in animal feed

The performances of Soxhlet extraction, dive-in Soxhlet extraction, microwave-assisted extraction (MAE), accelerated solvent extraction (ASE), fluidized-bed extraction (FBE), and ultrasonic extraction (UE) for the analysis of organochlorine pesticides in animal feed have been investigated. ASE and MAE provided significantly better extraction efficiency than Soxhlet extraction. The concentrations were 126.7 and 114.8%, respectively, of the values obtained by classical Soxhlet extraction, whereas the results from FBE and dive-in Soxhlet were comparable with those from the standard Soxhlet procedure. The reproducibility of FBE was the best, with RSDs ranging from 0.3 to 3.9%. Under the investigated operation conditions UE was not efficient, with the recoveries of target compounds being about 50% less than Soxhlet. Additionally, the performances of Soxhlet, dive-in Soxhlet, MAE, ASE and FBE were validated by determination of the certified reference material BCR-115. The results from the extraction techniques were in good agreement with the certified values.     

Direct ultrasonic agitation for rapid extraction of organic matter from airborne particulate

Direct ultrasonic extraction (DUE) is proposed as simple and rapid sample pretreatment method. This new approach is applied to the extraction of particulate organic matter (POM) from airborne particulate by using dichloromethane (DCM) or DCM/methanol (90/10, v/v) as extractant. The analytical determination was carried out by weighing the extractable POM on an electrobalance. Total recovery for POM could be obtained when the sample was extracted three times with 25–50 mL extractant each for about 5 min at 50 W ultrasonic power. In comparison with conventional Soxhlet extraction, less extraction time (total 15 min only) and solvent consumption(100 mL) were required by DUE. The efficiency of the DUE was similar or even higher than the routine Soxhlet method. Additionally, the new extractor is very simple and easy to use and can accelerate the extraction procedures of organic components from various solid samples.     

Extract with high 1,1-diphenyl-2-picrylhydrazyl (DPPH) inhibitory capability from pericarp and seed of mangosteen (Garcinia mangostana L.) using microwave-assisted extraction (MAE) two-phase solvent technique

The human body needs compounds that are antioxidants to prevent oxidative stress. Some parts of the mangosteen fruit (Garcinia mangostana L.) have been known as sources of bioactive compounds that have antioxidant properties. The pericarp and seeds of mangosteen were extracted using the MAE method to produce the extract with the greatest antioxidant activity. There are two types of solvent mixtures used in the extraction process: single-phase and two-phase solvents. The solvents used were ethanol (EtOH), ethyl acetate (EtOAc), isopropyl alcohol (IPA), and water. First, utilizing dried mangosteen pericarp powder as the raw material, a study was undertaken to determine the ideal operating conditions for the MAE process. A one-factor-at-a-time approach was used to find the best operating conditions. A mixture of solvents with varied ratios (mL/mL), extraction temperature (°C), extraction time (min), and solid to solvent ratio (g/mL) were applied as independent variables. Then, dried mangosteen seed powder extraction was carried out based on the best-operating conditions previously achieved. The DPPH scavenging activity, total phenolic content (TPC) value, and α-mangostin content of the two extracts were compared. It was discovered that the mangosteen pericarp extract showed higher antioxidant activity (IC₅₀ DPPH = 9.40 µg/mL) than the mangosteen seed extract (IC₅₀ DPPH = 37.54 µg/mL), even slightly better than ascorbic acid (IC₅₀ DPPH = 10.47 µg/mL). The best extract was produced from the bottom phase of two-phase solvent system (EtOAc:EtOH:Water 2:1:2), with an MAE temperature of 50 °C, a time of 4 min, and a solid-to-solvent ratio of 1:16. The TPC value of the best extract is 903.54 mgGAE/g extract, with a yield of 16.53 % and an α-mangostin concentration of 0.11 %.     

Combined microwave-assisted isolation and solid-phase purification procedures prior to the chromatographic determination of phenolic compounds in plant materials

A fast, sensitive and selective procedure employing a combination of microwave-assisted extraction (MAE) and solid phase extraction (SPE) was applied prior to liquid chromatographic identification and quantification of phenolic compounds in plant materials. MAE has been tested and optimized for the isolation of phenolic acids (gallic, protocatechuic, p-hydroxybenzoic, chlorogenic, vanilic, caffeic, syringic, p-coumaric, ferulic, sinapic, benzoic, m-coumaric, o-coumaric, rosmarinic, cinnamic acids) and 3,4-dihydroxybenzaldehyde, syringaldehyde, p-hydroxybenzaldehyde, and vanillin in various plants. The effects of experimental conditions on MAE efficiency, such as solvent composition, temperature, extraction time, have been studied. The extraction efficiencies were compared with those obtained by computer-controlled, two-step Soxhlet-like extractions. Plant extracts were purified and phenolic compounds were pre-concentrated using SPE on polymeric RP-105 SPE sorbent prior to HPLC analysis. Chromatographic separation was carried out on a Hypersil BDS C₁₈ column using a mobile phase consisted of 0.3% (v/v) acetic acid in water (solvent A) and methanol (solvent B) at flow rate 0.6 ml min⁻¹ and column temperature 30 °C with gradient elution.     

Direct ultrasonic agitation for rapid extraction of organic matter from airborne particulate

Direct ultrasonic extraction (DUE) is proposed as simple and rapid sample pretreatment method. This new approach is applied to the extraction of particulate organic matter (POM) from airborne particulate by using dichloromethane (DCM) or DCM/methanol (90/10, v/v) as extractant. The analytical determination was carried out by weighing the extractable POM on an electrobalance. Total recovery for POM could be obtained when the sample was extracted three times with 25-50 mL extractant each for about 5 min at 50 W ultrasonic power. In comparison with conventional Soxhlet extraction, less extraction time (total 15 min only) and solvent consumption (100 mL) were required by DUE. The efficiency of the DUE was similar or even higher than the routine Soxhlet method. Additionally, the new extractor is very simple and easy to use and can accelerate the extraction procedures of organic components from various solid samples.     

Analysis of Volatile Components of Pseudostellaria heterophylla (Miq.) Pax by Microwave-Assisted Solvent Extraction and GC–MS

Pseudostellaria heterophylla (Miq.) Pax or Taizishen (TZS) is one of the most popular Traditional Chinese Medicines in China, and is commonly used to treat various lung and spleen diseases. In this work focused microwave-assisted solvent extraction (MAE) coupled with gas chromatography–mass spectrometry has been used for analyzing volatile components of TZS. The main compound in the extract were palmitic acid (21.37%), 9,12-octadecadienoic acid ethylester (16.98%), trans-oleic acid (5.94%), chondrillasterol (3.99%), stigmast-7-en-3-ol (3.92%), 5,6-dihydroergosterol(2.48%), 1-monolinolein (2.35%). Compared with Soxhlet extraction, the much shorter extraction time and the similar components in the extract make MAE an excellent alternative for extraction of the components of TZS.     

Application of water as a solvent in microwave-assisted extraction for analysis of PCBs and CBzs in fly ash

Polychlorinated biphenyls (PCBs) and chlorobenzenes (CBzs) are two classes of dioxin precursors formed in municipal solid waste incinerators (MSWIs); they produce negative health effects similar to those of dioxins. Reducing the analytical time required for determining the concentrations of these compounds in MSWIs is important for quickly evaluating their importance and assessing associated health risks. In the present study, water is used as a safe and environmentally friendly solvent in microwave-assisted extraction (MAE) for PCB and CBz analyses. MAE is compared with traditional Soxhlet extraction (SE) to determine the extraction efficiencies. The evaluation of extraction efficiencies shows that MAE has a high extraction efficiency compared with that of SE when water content is lower than 60%. Furthermore, the extraction time and organic solvent consumption are reduced with MAE compared with SE.