Closed-vessel Microwave-assisted Extraction Research Articles

Optimization of microwave-assisted extraction of phenolic compounds from Inula britannica L. using the Box-Behnken design

A closed-vessel microwave-assisted extraction (MAE) of phenolic compounds from the aerial parts of Inula britannica L. using single-factor experiments and the Box-Behnken design with four independent variables (liquid-to-solid ratio, ethanol concentration, extraction time, and temperature) was investigated. The ANOVA results showed that the obtained model was significant at a 95 % confidence level. The extraction parameters for the maximal total phenolic content (46.19 mg GAE/g DM) were determined to be 15.13 ml/g liquid-to-solid ratio, 55.95 % EtOH, 73.74 ºC, and 5.73 min. Compared with classical maceration, the proposed MAE of phenolic compounds from I. britannica saves a lot of time and gives a high extraction yield.

Total Fat Gravimetric Method Workflow in Portuguese Olives Using Closed-Vessel Microwave-Assisted Extraction (MAE).

A simple and rapid method for the quantitation of total fat in olive samples is designed, evaluated, and presented. This method is based on an innovative closed-vessel microwave-assisted extraction (MAE) technique. A method was designed for olives, and some figures of merits were evaluated: limit of detection (LOD), limit of quantification (LOQ) and expanded uncertainty (U). The data obtained in these experiences show that the workflow of the MAE method in a closed container is statistically equivalent to the other two methods, showing in this case better performance indicators (LOD = 0.02%, LOQ = 0.06%, and U = 15%). In addition, it is also demonstrated that the complete MAE method workflow allows the determination of total fat in a maximum of 12 analyses simultaneously for about 100 min in each run, which is the capacity of the rotor. This is a much better productivity when compared to the traditional Soxhlet-based method. Considering the sample workflow, the closed-vessel MAE method greatly simplifies sample handling, therefore minimizing sample loss during sample preparation and reducing analysis time. When MAE is compared to NIR-based methods, the advantage comes from there being no need for any type of calibration in the sample matrix. The MAE method itself can be used to determine the reference value for NIR calibration purposes. The results obtained for CRM using MAE were equivalent to the ones shown on the certificate.

Optimization of microwave assisted extraction of simmondsins and polyphenols from Jojoba (Simmondsia chinensis) seed cake using Box-Behnken statistical design

A closed-vessel microwave-assisted extraction (MAE) of simmondsins and polyphenols from defatted Jojoba cake using Box-Benkhen design with four independent variables (solvent/cake ratio, ethanol concentration, extraction time and microwave power) was investigated. ANOVA results showed that the obtained models were significant at 95% confidence level. Optimal extraction conditions were found for highest values of microwave power (500 W) and extraction time (15 min) and for moderate values of solvent to cake ratio (41 – 45 mL/g). Optimum simmondsins yield (23.35%) was obtained with pure water as solvent. However, optimum polyphenols yield (2.33%) and ORAC antioxidant activity (656 µmol TE/g) were obtained with 46.79% and 42.04% ethanol in water, respectively. ORAC antioxidant activity was found to be well correlated to polyphenol and simmondsin contents. These results indicate that MAE is an effective technique for recovery of bioactive compounds for food and pharmaceutical industries from Jojoba by-products.

A method for rapid determination of arsenic species in vegetables using microwave-assisted extraction followed by detection with HPLC hyphenated to inductively coupled plasma-mass spectrometry.

Driven by the significant need for characterization of the chemical speciation of arsenic in food, this work developed a method for rapid determination of four common arsenic species, namely, arsenite, arsenate, monomethyl arsenic acid, and dimethyl arsenic acid, in vegetables using microwave-assisted extraction, followed by detection with high-performance liquid chromatography hyphenated to inductively coupled plasma-mass spectrometry. Initial screening results showed that microwave-assisted extraction using 1% HNO3 exhibited the highest overall efficiencies for all arsenic species without causing significant degradation of the organic ones. With the aid of response surface methodology, the optimum conditions established for extraction of arsenic species from vegetables were: 500mg of freeze-dried vegetable sample, extracted by closed vessel microwave-assisted extraction using 10mL of 2% v/v HNO3 at 90°C for 17min. Application of the method in the analysis of 24 market vegetable samples indicates that the extraction efficiencies for total arsenic species were in the range of 91.4-106%. Arsenite and arsenate were found to be the predominant arsenic species in the vegetables, which suggests that vegetable consumption could be an important route of inorganic arsenic exposure for the population with a heavy vegetable diet in arsenic polluted regions.

Simultaneous Determination of 11 Elements in Fly Ash by Inductively Coupled Plasma Orthogonal Acceleration Time-of-Flight Mass Spectrometry After Closed-Vessel Microwave-Assisted Extraction with Ammonium Fluoride

A method for simultaneous multi-element analysis of fly ash samples by inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry (oaTOF-ICP-MS) after closed-vessel microwave extraction with ammonium fluoride was introduced here. Corrosive and/or toxic acids like HF, HCl or HClO4, as well as HNO3, which are commonly used during sample preparation of the fly ash samples, are avoided in this method. The spectral effects due to the formation of different Cl, Na, K, Ca, Mg-containing polyatomic species interfering with the determination of a number of elements like As, Se or Ni during the oaTOF-ICP-MS analysis are negligible. Under the optimum experimental extraction conditions evaluated using a fractional factorial design (10 mg of the sample extracted with 5 mL of 140 g/L NH4F for 10 min at 200°C), analysis of the resulting supernatant with Rh as an internal standard enabled precise and accurate simultaneous determination of 11 elements (Li, Be, Ni, As, Se, Rb, Sb, Cs, W, Tl and U) at trace and ultratrace levels. The accuracy was assessed by analysing two certified reference materials, namely Fine Fly Ash CTA-FFA-1 and Constituent Elements in Coal Fly Ash Standard Reference Material® 1633b. The precision of the reported method was better than 10%.

Closed-vessel miniaturised microwave-assisted EDTA extraction to determine trace metals in plant materials

The demonstration of an innovative miniaturised closed-vessel microwave-assisted extraction (µMAE) method under the use of EDTA (µMAE-EDTA) for determination of trace metal contents in grassland (Lolio-Cynosuretum) was examined by ICP-OES. The evaluation of the method was done by comparison of the results with another miniaturised closed-vessel microwave HNO3 method (µMAE-H) and with a macro-scale microwave procedure (MAE-H). Concerning their homogeneity certified plant reference materials (CRMs) were used for validation of the applicability of µMAE-EDTA procedure. For CRMs and 72 real plant samples, no significant differences were found between µMAE-EDTA and MAE-H in the determination of Cd, Co, Cu, Mn, Ni, Pb, and Zn contents. Recovery rates achieved from µMAE-EDTA for CRMs ranged between 100.0–102.6% for the investigated elements. The key characteristics of µMAE-EDTA for determination of trace metal contents in plant samples are: (i) suitability as a high-throughput procedure; (ii) consumption of minimum volume of extracting agent and minimum amount of sample; and (iii) combination of fast, safe and environmentally friendly extraction procedure.

An efficient chemical analysis of phenolic acids and flavonoids in raw propolis by microwave-assisted extraction combined with high-performance liquid chromatography using the fused-core technology

A closed-vessel microwave-assisted extraction (MAE) technique was optimized for the first time for the extraction of polyphenols from raw propolis. The results obtained by means of response surface experimental design methodology showed that the best global response was reached when the extraction temperature was set at 106°C, the solvent composition close to EtOH–H2O 80:20 (v/v), with an extraction time of 15min. In comparison with other techniques, such as maceration, heat reflux extraction (HRE) and ultrasound-assisted extraction (UAE), the extraction with MAE was improved by shorter extraction time and lower volume of solvent needed.The HPLC analyses of propolis extracts were carried out on a fused-core Ascentis Express C18 column (150mm×3.0mm I.D., 2.7μm), with a gradient mobile phase composed by 0.1% formic acid in water and acetonitrile. Detection was performed by DAD and MS.The method validation indicated that the correlation coefficients were >0.999; the limit of detection was in the range 0.5–0.8μg/ml for phenolic acids and 1.2–3.0μg/ml for flavonoids; the recovery range was 95.3–98.1% for phenolic acids and 94.1–101.3% for flavonoids; the intra- and inter-day %RSD values for retention times and peak areas were ≤0.3 and 2.2%, respectively.The quali- and quantitative analysis of polyphenols in Italian samples of raw propolis was performed with the validated method. Total phenolic acids ranged from 5.0 to 120.8mg/g and total flavonoids from 2.5 to 168.0mg/g.The proposed MAE procedure and HPLC method can be considered reliable and useful tools for the comprehensive multi-component analysis of polyphenols in propolis extracts to be used in apitherapy.

Rapid extraction and determination of atrazine and its degradation products from microporous mineral sorbents using microwave-assisted solvent extraction followed by ultra-HPLC-MS/MS

We have evaluated three methods for the extraction of atrazine and six of its degradation products from microporous mineral sorbents. Soxhlet extraction and ultrasonic extraction, which work well on soils and sediments, recover only <15 % of the atrazine from a dealuminated Y zeolite. Closed-vessel microwave-assisted extraction, in contrast, gives much better recoveries. This is attributed to the accelerated mass transfer at elevated temperatures and the displacement by the solvent forced into the mineral micropores under elevated pressures. Under the optimized conditions, the recovery of atrazine from the hydrophilic Y zeolites (Si/Al ratios <8) is almost quantitative, and ∼77 % for the more hydrophobic ones. The extraction efficiencies for the degradation products of atrazine in the hydrophilic zeolites (74.1–100 %) are also higher than those in the hydrophobic ones (22.3–44.2 %). The extracted compounds were quantified by a combination of ultra-HPLC and tandem MS and resulted in detection limits between 0.04 and 1.41 mg kg−1 on a hydrophilic Y zeolite (Si/Al = 2.55), and of 0.09–2.35 mg kg−1 on a hydrophobic zeolite (Si/Al = 15). The method was applied to study the degradation of atrazine sorbed on dealuminated Y zeolites.

Improved extraction of vegetable oils under high-intensity ultrasound and/or microwaves

Ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) techniques have been employed as complementary techniques to extract oils from vegetable sources, viz, soybean germ and a cultivated marine microalga rich in docosahexaenoic acid (DHA). Ultrasound (US) devices developed by ourselves, working at several frequencies (19, 25, 40 and 300kHz), were used for US-based protocols, while a multimode microwave (MW) oven (operating with both open and closed vessels) was used for MAE. Combined treatments were also studied, such as simultaneous double sonication (at 19 and 25kHz) and simultaneous US/MW irradiation, achieved by inserting a non-metallic horn in a MW oven. Extraction times and yields were compared with those resulting from conventional procedures. With soybean germ the best yield was obtained with a ‘cavitating tube’ prototype (19kHz, 80W), featuring a thin titanium cylinder instead of a conventional horn. Double sonication, carried out by inserting an immersion horn (25kHz) in the same tube, improved the yield only slightly but halved the extraction time. Almost comparable yields were achieved by closed-vessel MAE and simultaneous US/MW irradiation. Compared with conventional methods, extraction times were reduced by up to 10-fold and yields increased by 50–500%. In the case of marine microalgae, UAE worked best, as the disruption by US of the tough algal cell wall considerably improved the extraction yield from 4.8% in soxhlet to 25.9%. Our results indicate that US and MW, either alone or combined, can greatly improve the extraction of bioactive substances, achieving higher efficiency and shorter reaction times at low or moderate costs, with minimal added toxicity.

A comparative study of solvent extraction of total petroleum hydrocarbons in soil

Three non-specific methods for the extraction of total petroleum hydrocarbons (TPH) from soil into organic solvent were compared. The techniques used for sample preparation were Soxhlet extraction, closed-vessel microwave-assisted extraction, and CEN shake extraction. The total concentrations of extracted compounds in the boiling point range of C10–C40 were determined by gas chromatography with flame ionization detection. The best recovery (99%) and repeatability (±3%) from standard oil mixtures were obtained with microwave-assisted extraction. However, the different extraction methods exhibited different behaviour when spiked soil samples were extracted. The best repeatability was obtained with CEN shake extraction (±6%) but the repeatability values for Soxhlet and microwave-assisted methods were quite high (>20%). However, the larger uncertainties of the latter extraction methods does not necessarily limit the applicability of these methods to the determination of petroleum hydrocarbons in soil, as in the assessment of soil contamination the expanded uncertainty of the result is usually not limited by analytical uncertainty, but rather by the uncertainty of the primary sampling stage. However, distinctive variation found in the chromatographic profiles illustrates that discretion should be obeyed when chromatograms obtained after application of different extraction methods on petroleum contaminated samples are to be used in the fingerprinting or age dating studies. Otherwise, misleading conclusions concerning the age of spillage could be drawn.

Determination of mercury species in fish reference materials by gas chromatography-atomic fluorescence detection after closed-vessel microwave-assisted extraction

A simple and rapid method has been developed for speciation analysis of inorganic mercury and monomethylmercury (MMHg) in biological tissues. The procedure is based on the quantitative closed-vessel microwave-assisted leaching of mercury from biological samples with an alkaline extractant. The extracted mercury species are ethylated and analysed by capillary gas chromatography coupled to an atomic fluorescence detector via pyrolysis (CGC-pyro-AFS). The coupling between capillary gas chromatography and atomic fluorescence detector was optimized with the aim of minimizing the detection limits and time necessary for the species-selective determination of mercury compounds. The use of closed-vessel microwave-assisted extraction along with no clean-up steps before the ethylation leads to a significant total analysis time decrease with respect to similar procedures. The detection limit was 2 pg for MMHg (as Hg) and 1 pg for inorganic mercury. The method was validated by the analysis of DORM-2 (dogfish muscle) and DOLT-3 (dogfish liver) certified reference materials. The inorganic mercury and methylmercury concentrations found were in good agreement with the certified values. Recovery studies of fish muscle tissue spiked with inorganic mercury and MMHg were done to check the reliability of the method. In all cases satisfactory recoveries (92–105%) were obtained.

Microwave-Assisted Extraction and Accelerated Solvent Extraction with Ethyl Acetate–Cyclohexane before Determination of Organochlorines in Fish Tissue by Gas Chromatography with Electron-Capture Detection

Focused open-vessel microwave-assisted extraction (FOV-MAE), closed-vessel microwave-assisted extraction (CV-MAE), and accelerated solvent extraction (ASE) were used for extraction before determination of organochlorine compounds (polychlorinated biphenyls, DDT, toxaphene, chlordane, hexachlorobenzene, hexachlorocyclohexanes, and dieldrin) in cod liver and fish fillets. Wet samples were extracted without the time-consuming step of lyophilization or other sample-drying procedures. Extractions were performed with the solvent mixture ethyl acetate-cyclohexane (1 + 1, v/v), which allowed direct use of gel-permeation chromatography without solvent exchange. For FOV-MAE, the solvent mixture removed water from the sample matrix via azeotropic distillation. The status of water removal was controlled during extraction by measuring the temperature of the distillate. After water removal, the temperature of the distillate increased and the solvent mixture became less polar. Only the pure extraction solvent allowed quantitative extraction of the organochlorine compounds. For CV-MAE, water could not be separated during the extraction. For this reason, the extraction procedure for wet fish tissue required 2 extraction steps: the first for manual removal of coextracted water, and the second for quantitative extraction of the organochlorine compounds with the pure solvent. Therefore, CV-MAE is less convenient for samples with high water content. For ASE, water in the sample was bound with Na2SO4. The reproducibility for each technique was very good (relative standard deviation was typically <10%); the slightly varying levels were attributed to deviations during sample cleanup and the generally low levels.