Microwave-assisted extraction of tanshinones from Salvia miltiorrhiza bunge with analysis by high-performance liquid chromatography

A novel microwave-assisted extraction (MAE) method has been developed for the extraction and determination of tanshinones (tanshinone IIA, cryptotanshinone and tanshinone I) from the root of Salvia miltiorrhiza bunge with analysis by HPLC. Various experimental conditions were investigated to optimize the percentage extraction. Under appropriate MAE conditions, such as ethanol concentrations of 95% (v/v), MAE for 2 min, liquid/solid ratio of 10:1 (ml/g), the percentage extraction can reach high in a short time. The percentage extraction (tanshinone IIA: 0.29%; cryptotanshinone: 0.23%; tanshinone I: 0.11%) by MAE was the same or even higher than conventional extraction methods. MAE only needs 2 min, but extraction at room temperature, heat reflux extraction, ultrasonic extraction and Soxhlet extraction need 24 h, 45 min, 75 min and 90 min, respectively. MAE was also available in pilot plant form for larger scale extraction.     

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.     

Continuous microwave-assisted extraction coupled on-line with liquid-liquid extraction: determination of aliphatic hydrocarbons in soil and sediments

This paper describes a new extraction method for the determination of aliphatic hydrocarbons (AHs) in soil and sediment samples, using continuous microwave-assisted extraction (MAE) combined with liquid-liquid extraction, for clean-up purposes. Analytical determinations were carried out by gas chromatography coupled with impact ionization mass spectrometry. The influence of the experimental conditions was tested using an agricultural soil spiked with standards (stored at 4 degrees C for 1 month) as reference soil. Maximum extraction efficiencies (80-90%) were achieved using 0.1-1.0g of sample, 60microl of water and 3ml of n-hexane (extractant) and 5min of extraction time; less than 70% of the most volatile hydrocarbons (C(9)-C(12)) were recovered since many evaporated during the drying step of the sample. MAE was compared with a conventional extraction method such as Soxhlet and a good agreement in the results was obtained (average recovery percentage value of 105% by comparing MAE against Soxhlet). Quality parameters such as linear range (0.5-800microg/g), limits of detection (LODs) (0.1-0.2microg/g) and precision (RSD, 4-6%) were determined using spiked soil samples. This method was successfully applied to the analysis of aliphatic hydrocarbons (C(9)-C(27) including pristane and phytane) in contaminated real samples.     

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.     

Comparison of various techniques for the extraction and determination of antioxidants in plants

The following extraction techniques have been used for extracting antioxidants (apigenin, coumarin, esculetin, umbelliferone, bergapten, quercetin, rutin, scopoletin and xanthotoxin) from plant material: supercritical fluid extraction, pressurized liquid extraction, extraction by means of Soxhlet apparatus, ultrasonic extraction in ultrasonic bath, and by means of ultrasonic probe. The analytical method based on HPLC?UV detection for the determination of selected antioxidants was developed. For all extracts the antioxidant capacity based on the reduction of free 2,2‐diphenyl‐1 ‐picrylhydrazyl radical was also determined. Comparing all results the ultrasonic probe method using 0.75 g of sample extracted by 50 mL of acetonitrile in water (30%, v/v) for 25 min at room temperature and with amplitude at 60% (equal to 90 W) without pulsation was evaluated as the best tool. The most significant indicator demonstrating this statement is the antioxidant capacity expressed as gallic acid equivalent where the ultrasonic probe method showed the best results in 10 of 16 samples. Also the operability of ultrasonic probe extraction method compared to other tested methods is more favorable.     

A cost effective,sensitive, and environmentally friendly sample preparation method for determination of polycyclic aromatic hydrocarbons in solid samples

A simple, cost effective, and yet sensitive sample preparation technique was investigated for determining Polycyclic Aromatic Hydrocarbons (PAHs) in solid samples. The method comprises ultrasonic extraction, Stir Bar Sorptive Extraction (SBSE), and thermal desorption–gas chromatography–mass spectrometry to increase analytical capacity in laboratories. This method required no clean-up, satisfied PAHs recovery, and significantly advances cost performance over conventional extraction methods, such as Soxhlet and Microwave Assisted Extraction (MAE). This study evaluated three operational parameters for ultrasonic extraction: solvent composition, extraction time, and sample load. A standard material, SRM 1649 a (urban dust), was used as the solid sample matrix, and 12 priority PAHs on the US Environmental Protection Agency (US EPA) list were analyzed. Combination of non-polar and polar solvents ameliorated extraction efficiency. Acetone/hexane mixtures of 2:3 and 1:1 (v/v) gave the most satisfactory results: recoveries ranged from 63.3% to 122%. Single composition solvents (methanol, hexane, and dichloromethane) showed fewer recoveries. Comparing 20 min with 60 min sonication, longer sonication diminished extraction efficiencies in general. Furthermore, sample load became a critical factor in certain solvent systems, particularly MeOH. MAE was also compared to the ultrasonic extraction, and results determined that the 20-min ultrasonic extraction using acetone/hexane (2:3, v/v) was as potent as MAE. The SBSE method using 20 mL of 30% alcohol-fortified solution rendered a limit of detection ranging from 1.7 to 32 ng L⁻¹ and a limit of quantitation ranging from 5.8 to 110 ng L⁻¹ for the 16 US EPA PAHs.     

Optimization and comparison of MAE, ASE and Soxhlet extraction for the determination of HCH isomers in soil samples

The microwave-assisted extraction (MAE), accelerated solvent extraction (ASE) and Soxhlet extraction of two isomers of hexachlorocyclohexane, alpha-HCH and gamma-HCH, from a polluted landfill soil have been optimized following different experimental designs. In the case of microwave-assisted extraction, the following variables were considered: pressure, extraction time, microwave power, percentage of acetone in n-hexane mixture and solvent volume. When ASE extraction was studied the variables were pressure, temperature and extraction time. Finally, the percentage of acetone in n-hexane mixture and the extraction time were the only variables studied for Soxhlet extraction. The concentrations obtained by the three extraction techniques were, within their experimental uncertainties, in good agreement. This fact assures the possibility of using both ASE and MAE techniques in the routine determination of lindane in polluted soils and sediments.     

An efficient and fast microwave-assisted extraction method developed for the simultaneous determination of 18 organochlorine pesticides in sediment

An efficient and fast microwave-assisted extraction (MAE) method followed by gas chromatographic separation with mass spectrometric detection (GC–MS) was developed for the extraction of 18 organochlorine pesticides (OCPs) from sediment. Parameters affecting the MAE procedure such as the type and volume of the extraction solvent, irradiation power, temperature and irradiation time were successfully optimised. Under the optimal conditions, extraction efficiencies in the range of 73.4–119% were obtained with THF–HEX (9:1, v/v) for all OCPs studied. The method was linear over the range of 2.9–5000 ng g^?1 with determination coefficients (r²) higher than 0.992 for all analytes. The limits of detection, LODs (S/N = 3), obtained varied from 1.0 to 2.2 ng g^?1 and limits of quantification, LOQs (S/N = 10) were between 2.9 and 6.8 ng g^?1. The proposed method was successfully applied to the analysis of real sediment samples and acceptable recoveries from 70.1 to 124% with RSDs ≤14.8% were obtained. 10 OCPs were determined below their LOQ and 8 OCPs in the range of 124–2830 ng g^?1. The MAE method was compared with Soxhlet, shake flask and ultrasonic solvent extraction techniques. Thus, the MAE–GC–MS method could efficiently be used for selective extraction and quantification of the target analytes from the complex sediment matrices.     

Microwave-assisted extraction of coumarin and related compounds from Melilotus officinalis (L.) Pallas as an alternative to Soxhlet and ultrasound-assisted extraction

Soxhlet extraction, ultrasound-assisted extraction (USAE) and microwaves-assisted extraction (MAE) in closed system have been investigated to determine the content of coumarin, o-coumaric and melilotic acids in flowering tops of Melilotus officinalis. The extracts were analyzed with an appropriate HPLC procedure. The reproducibility of extraction and of chromatographic analysis was proved. Taking into account the extraction yield, the cost and the time, we studied the effects of extraction variables on the yield of the above-mentioned compounds. Better results were obtained with MAE (50% v/v aqueous ethanol, two heating cycles of 5 min, 50 degrees C). On the basis of the ratio extraction yield/extraction time, we therefore propose MAE as the most efficient method.     

Evaluation of microwave-assisted extraction for the analysis of polychlorinated biphenyls and organochlorine pesticides in fish

The efficiency of microwave-assisted extraction (MAE) was evaluated for the analysis of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in fish. An isotope dilution method was used for quantification via analysis of the samples by gas chromatography and mass spectrometry. MAE solvent, temperature, and time were optimized, and observed concentrations were compared. The MAE results were also compared to those of other extraction techniques (Soxhlet extraction, pressurized liquid extraction, saponification, and homogenization). Concentrations of PCBs and OCPs obtained by MAE at 120 degrees C for 10 min were comparable to those by the other techniques. The results suggest that MAE can be used for the analysis of PCBs and OCPs in fish.     

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.     

Development of microwave assisted extraction for the simultaneous determination of isoflavonoids and saponins in radix astragali by high performance liquid chromatography

A microwave assisted extraction (MAE) procedure was first developed for the simultaneous determination of isoflavonoids and astragalosides in Radix Astragali (RA). MAE showed the highest extraction efficiency when compared to Soxhlet, reflux, and ultrasonic extraction. It was found that flavonoid glycoside malonates were converted into their related glycosides during the prolonged conventional extraction, thus affecting the reproducibility. However, the conversion was inhibited when using MAE. After being optimized in terms of solvents, microwave power, and irradiation time, MAE was used for the simultaneous determination of isoflavonoids and astragalosides in RA with HPLC-UV-evaporative light scattering detection (ELSD). Our results indicated that extraction by MAE was more effective than by other conventional techniques. Moreover, the MAE method followed by HPLC-UV-ELSD determination was a simple, rapid, and reliable method for the quality assessment of RA.     

Microwave-assisted extraction versus Soxhlet extraction in the analysis of 21 organochlorine pesticides in plants

A method to determine 21 organochlorine pesticides in vegetation samples using microwave-assisted extraction (MAE) is described and compared with Soxhlet extraction. Samples were extracted with hexane–acetone (1:1, v/v) and the extracts were cleaned using solid-phase extraction with Florisil and alumine as adsorbents. Pesticides were eluted with hexane–ethyl acetate (80:20, v/v) and determined by gas chromatography and electron-capture detection. Recoveries obtained (75.5–132.7% for Soxhlet extraction and 81.5–108.4% for MAE) show that both methods are suitable for the determination of chlorinated pesticides in vegetation samples. The method using microwave energy was applied to grass samples from parks of A Coruña (N.W. Spain) and to vegetation from the contaminated industrial area of Torneiros (Pontevedra, N.W. Spain).     

Optimization and comparison of MAE, ASE and Soxhlet extraction for the determination of HCH isomers in soil samples

The microwave-assisted extraction (MAE), accelerated solvent extraction (ASE) and Soxhlet extraction of two isomers of hexachlorocyclohexane, α-HCH and γ-HCH, from a polluted landfill soil have been optimized following different experimental designs. In the case of microwave-assisted extraction, the following variables were considered: pressure, extraction time, microwave power, percentage of acetone in n-hexane mixture and solvent volume. When ASE extraction was studied the variables were pressure, temperature and extraction time. Finally, the percentage of acetone in n-hexane mixture and the extraction time were the only variables studied for Soxhlet extraction. The concentrations obtained by the three extraction techniques were, within their experimental uncertainties, in good agreement. This fact assures the possibility of using both ASE and MAE techniques in the routine determination of lindane in polluted soils and sediments. Received: 28 January 2000 / Revised: 28 March 2000 / Accepted: 31 March 2000     

Combining microwave-assisted extraction and liquid chromatography–ion-trap mass spectrometry for the analysis of hexabromocyclododecane diastereoisomers in marine sediments

An efficient microwave-assisted extraction (MAE) procedure coupled with high performance liquid chromatography–electrospray-ion-trap mass spectrometry (HPLC–ESI-ITMS) has been evaluated to determine hexabromocyclododecane diastereoisomers (α-, β- and γ-HBCD) in marine sediments. The composition of the LC mobile phase (consisting of water, methanol and acetonitrile) and the parameters of electrospray ionization (ESI) were evaluated to obtain chromatographic baseline separation and high sensitivity for the detection of these diastereoisomers. The effects of various operating parameters on the quantitative extraction of the HBCDs through MAE were systematically investigated. The three diastereoisomers were then quantitated by HPLC–ITMS employing ESI operated in the negative ionization mode. The HBCDs were extracted from the sediments through MAE using 40 mL of acetone/n-hexane (1/3, v/v) at 90 °C for 12 min. The limits of quantitation (LOQ) ranged from 25 to 40 pg/g (dry weight) in 5 g of the sediment samples. The recoveries of the HBCDs in spiked sediment samples ranged from 68 to 91% (relative standard derivation: 2–11%). The extraction efficiency of the MAE technique was also compared with Soxhlet extraction and pressurized liquid extraction.     

Microwave-assisted extraction of C60 and C70 from fullerene soot

Microwave-assisted extraction (MAE) was examined as an alternative to the traditional Soxhlet method of extracting C₆₀ and C₇₀ from fullerene soot. MAE of 0.20 g of fullerene soot with 95:5 toluene–acetonitrile yielded greater than 7.8 mg of C₆₀ and greater than 0.54 mg of C₇₀ in 4 min with no further increase in yield after 30 min of irradiation. By comparison, exhaustive Soxhlet extraction of the same size sample with the same solvent yielded 7.1 mg of C₆₀ and 0.58 mg of C₇₀ in 340 min. Reextraction by MAE of soot initially extracted by Soxhlet increased the yield of Soxhlet alone. Although MAE was limited to less than 0.5-g sample per extraction vessel, multiple samples were extracted with minimal increased extraction time and no reduction in the amount of material recovered.     

Optimisation and comparison of microwave-assisted extraction and Soxhlet extraction for the determination of polychlorinated biphenyls in soil samples using an experimental design approach

Optimisation of microwave-assisted extraction (MAE) for the extraction of polychlorinated biphenyls (PCBs) from soil samples has been accomplished using an experimental design approach. Variables studied have been: percentage of acetone (v/v) in an acetone:n-hexane mixture, solvent volume, extraction time, microwave power and pressure inside the extraction vessel. Five samples of a certified soil (CRM 481) have been extracted under the optimum conditions of the developed method and the results have been compared to those obtained by Soxhlet extraction. Good recoveries (>95%) have been obtained for all the PCBs studied. All extracts have been analysed by gas chromatography/mass spectrometry (GC/MS) and an optimum determination method for the electron impact mass spectrometric (EIMS) has also been developed.     

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.     

Optimisation of a microwave-assisted extraction method for the simultaneous determination of haloanisoles and halophenols in cork stoppers

This study presents a method based on the use of microwave-assisted extraction (MAE) for the quantitative analysis of 2,4,6-trichloroanisole (TCA), 2,3,4,6-tetrachloroanisole (TeCA), pentachloroanisole (PCA), 2,4,6-tribromoanisole (TBA), 2,4,6-trichlorophenol (TCP), 2,3,4,6-tetrachlorophenol (TeCP), pentachlorophenol (PCP) and 2,4,6-tribromophenol (TBP) in cork stoppers. The influential parameters of the MAE procedure (extraction time, temperature and solvent volume) were optimised using a central composite experimental design combined with desirability functions. The optimal conditions identified were temperature 170 degrees C, solvent volume 35 mL and extraction time 90 min. MAE extracts were concentrated and derivatised prior to separation and quantification by gas chromatography with electron capture detection. To evaluate the applicability of the proposed MAE method, recovery results were compared with those obtained with the Soxhlet extraction method; the results were similar with both extraction methods. The new method was also satisfactorily applied to real cork stopper samples.     

Microwave-assisted extraction of phenolics from Canarium album L. and identification of the main phenolic compound

Microwave-assisted extraction (MAE) was applied in the extraction of phenolics from Canarium album L. Effects of various conditions including the solvent, solvent to material ratio, microwave power and irradiation time on extraction yield of phenolics were investigated. In terms of the optimal conditions of MAE, it was concluded that 70% (v/v) of ethanol was the proper extraction solvent, the solvent to material ratio was 10 : 1 (mL : g), and the microwave power and irradiation time were 600 W and 15 s, respectively. Compared with normal stirring extraction and ultrasound-assisted extraction, the MAE of phenolics from C. album L. was more time efficient and gave a high extraction rate. More than 1.2% extraction yield was achieved with MAE, and the purity of the phenolics in the extract product was up to 25%. In addition, by ultraviolet-visible (UV) spectrometry and electrospray ionised mass spectrometry (ESI/MS), the main phenolic compound in the extract product was identified as gallic acid.