Microwave-assisted Extraction Procedure Research Articles

Optimization of a rapid microwave-assisted extraction method for the simultaneous determination of opiates, cocaine and their metabolites in human hair

A rapid and cleanup-free microwave-assisted extraction (MAE) method is proposed for the simultaneous extraction of six illegal drugs of abuse – cocaine, benzoylecgonine (BZE), cocaethylene (CCE), morphine, 6-monoacethylmorphine (6AM) and codeine – from human hair samples. The analytes were determined using high performance liquid chromatography (HPLC) with photodiode array UV detection. The influence of several variables on the efficiency of the MAE procedure was investigated in detail by a multi-objective optimization approach based on a hybrid experimental design (17 experiments) and desirability functions. Six drugs were successfully extracted from human hair with recoveries close to 100% and good reproducibility (<3.6% RSD) under the optimal MAE conditions: 11 mL dichloromethane (DCM) extraction solvent, 60 °C extraction temperature, 9 min extraction time and 0.5 mL of methanol (MeOH) added to 50 mg of the hair sample in the extraction vessels. Limits of quantification of 0.2 ng mg −1 were found for the studied compounds. A comparison of sample preparation procedures, including MAE, enzymatic digestion and digestion by aqueous acids, was also conducted. The results indicated that the global behaviour of sample procedures provided similar satisfactory recoveries ranging from 86 to 100%. Indeed, the MAE procedure resulted in a reduction of extraction time by 100-fold and the elimination of cleanup steps. Slightly higher recoveries of morphine, 6AM, BZE and CCE, at 1 ng mg −1 concentration level and cocaine at 40 ng mg −1 concentration level, were achieved using MAE. Lastly, the proposed MAE method was applied to several human hair samples from multidrug abusers.

An efficient microwave‐assisted extraction process of stevioside and rebaudioside‐A from Stevia rebaudiana (Bertoni)

Stevioside and rebaudioside-A are major low-calorie diterpene steviol glycosides in the leaves of Stevia rebaudiana. They are widely used as natural sweeteners for diabetic patients, but the long extraction procedures required and the optimisation of product yield present challenging problems. To develop a rapid and effective methodology for the extraction of stevioside and rebaudioside-A from S. rebaudiana leaves and to compare yields using different extraction techniques. Dried and powdered leaves of S. rebaudiana were extracted by conventional, ultrasound and microwave-assisted extraction techniques using methanol, ethanol and water as single solvents as well as in binary mixtures. Conventional cold extraction was performed at 25 degrees C for 12 h while ultrasound extraction was carried out at temperature of 35 +/- 5 degrees C for 30 min. Microwave-assisted extraction (MAE) was carried out at a power level of 80 W for 1 min at 50 degrees C. MAE yielded 8.64 and 2.34% of stevioside and rebaudioside-A, respectively, while conventional and ultrasound techniques yielded 6.54 and 1.20%, and 4.20 and 1.98% of stevioside and rebaudioside-A, respectively. A rapid and efficient method has been developed for the extraction of stevioside and rebaudioside-A in optimum yields using MAE procedure. This method has the advantage of rapid extraction and fast screening of a large number of S. rebaudiana samples for assessment of planting material. MAE saves considerable time, energy and has implications in the quality assessment of stevioside and rebaudioside-A prior to their industrial production from the leaves of S. rebaudiana.

Optimization of microwave-assisted extraction procedure for zinc and copper determination in food samples by Box-Behnken design

This article describes the application of response surface methodology (RSM) to the development of a procedure for zinc and copper determination by flame atomic absorption spectrometry (FAAS) in food samples after extraction by a microwave system. A Box-Behnken matrix was used to find optimal conditions for the procedure through a response surface study. Three variables “irradiation power; time; and temperature” were regarded as factors in the optimization study. The working conditions were established as a compromise between optimum values found for each analyte taking into consideration the robustness of the procedure. These values were 97 °C, 90 W and 9.0 min, for temperature, irradiation power and time, respectively. The accuracy of the optimized procedure was evaluated by the analysis of certified reference materials. The method was applied to the determination of copper and zinc in wheat flour and corn flour samples.

Determination of Anti-Tumor Constitute Mollugin from Traditional Chinese Medicine Rubia cordifolia: Comparative Study of Classical and Microwave Extraction Techniques

Rubia cordifolia is a common traditional Chinese medicine (TCM) used for centuries for the treatment of cough, inflammation of the joints, uterine hemorrhage, and uteritis. Mollugin is a major active component present in R. cordifolia and recognized as a potential anti-tumor compound. In this work, a microwave-assisted extraction (MAE) method has been developed for extracting mollugin from R. cordifolia. Several variables that can potentially affect the extraction yield, namely extracting solvent, microwave power, extraction time, and solid-liquid ratio were optimized. The separation and quantitative determination of mollugin was carried out by HPLC with UV detection at 254 nm. Under appropriate MAE conditions, such as extraction time of 4 min, ethanol concentration of 70% (v/v), microwave power of 460 W, and solid-liquid ratio of 1:20 (g/mL), the extraction yield of mollugin from R. cordifolia with MAE was higher than conventional extraction methods such as Soxhlet extraction, heat reflux extraction, and ultrasonic-assisted extraction. Due to the considerable saving in time and its higher extraction yield, the proposed MAE procedure was obviously a more rapid and effective sample preparation technique.

Determination of main taxoids in Taxus species by microwave‐assisted extraction combined with LC‐MS/MS analysis

A method based on microwave-assisted extraction (MAE) has been developed for the determination of paclitaxel and five related taxoids, namely 10-deacetylbaccatin III (10-DAB III), cephalomannine, 10-deacetylpaclitaxel (10-DAT), 7-xyl-10- deacetylpaclitaxel (7-xyl-10-DAT), and 7-epi-10-deacetylpaclitaxel (7-epi-10-DAT) in Taxus species in this study. The influential parameters of the MAE procedure were optimized, and the optimal conditions were as follows: extraction solvent 80% ethanol solution, solid/liquid ratio 1:10 (g/mL), temperature 50 degrees C, and three extraction cycles, each cycle 10 min. The method validation for LC-MS/MS analysis was performed. The LOD and LOQ were 3.16-9.20 and 12.20-30.45 ng/mL, respectively. Repeatability and reproducibility for the six taxiods with RSD ranged from 2.78 to 3.85% and from 5.26 to 6.60%. The recoveries of the method for the six taxoids were 92.6-105.6%. The developed MAE-LC-MS/MS method was also successfully applied to determine the contents of six taxoids in different Taxus species.

Quantitative determination of chlorogenic acid in Honeysuckle using microwave-assisted extraction followed by nano-LC-ESI mass spectrometry

The chlorogenic acid (CA) in Honeysuckle is determined and identified by nano-liquid chromatography-electrospray ionization mass spectrometry (nano-LC-ESI/MS) after extraction with microwave-assisted extraction (MAE). As a new sample preparation method for Honeysuckle, the MAE procedure is optimized, validated and compared with conventional methods including reflux extraction (RE) and ultrasonic extraction (USE). It is found that MAE gives the best result due to the highest extraction efficiency within shortest extraction time (only 4 min). Here, CA is determined by nano-LC-ESI/MS based on the calibration curve of its authentic standard. The method linearity, detection limit, precision and recovery are studied. The results show that the combined MAE and nano-LC-ESI/MS method has a linearity ( R 2 0.991, 0.8–20 ng mL −1), a low limit of detection (0.5 ng mL −1), good precision (R.S.D. = 2.54%) and a recovery (84.8%). The experiment has demonstrated that the nano-LC-ESI/MS following MAE is a fast and reliable method for quantitative analysis of CA in Honeysuckle.

Speciation of heavy metals in untreated sewage sludge by using microwave assisted sequential extraction procedure

A fast microwave assisted extraction procedure was developed and optimized for their eventual exploitation in the three-stage sequential extraction procedure proposed by modified BCR protocol (the community Bureau of Reference now the European Union "Measurement and Testing Programme"). The effects of the microwave treatment on the extraction of Cd, Cr, Cu, Ni, Pb and Zn from untreated sewage sludge collected from Hyderabad city (Pakistan) were compared with those obtained from sequential BCR extraction procedure. In sequential BCR method, each extraction step takes 16 h, where as with the use of compromised microwave conditions, extraction steps could be completed in about 120 s, for each step, respectively. Extractable Cd, Cr, Pb and Ni obtained by both comparable methodologies were measured by electrothermal atomic absorption spectrometry (ETAAS), while for Cu and Zn flame atomic absorption spectrometry (FAAS) was used. The validations of both extraction techniques were compared by the analysis of certified reference material of soil amended with sewage sludge (BCR 483). The results of the partitioning study of untreated waste water sewage sludge, indicate that more easily mobilized forms (step 1) were predominant for Cd, Ni and Zn (28.3, 28.4 and 43.7%), in contrast, the largest amount of Cd and Pb (66.4 and 72.8%) was associated with the iron/manganese oxide while Cr and Ni (71.2 and 38.7%) in organic matter/sulphide fractions. The overall metal recoveries in steps 1-3 (excluding residual step) were 95.3-104% of those obtained with the sequential BCR protocol. The accuracy of the proposed microwave extraction method (expressed as %R.S.D.) was lower than 10% for all metals.

Speciation Analysis of Mercury in Cereals by Liquid Chromatography Chemical Vapor Generation Inductively Coupled Plasma-Mass Spectrometry

A simple and rapid procedure for the separation and determination of inorganic, methyl, and ethyl mercury compounds was described using liquid chromatography (LC) followed by vapor generation inductively coupled plasma-mass spectrometry (VG-ICP-MS). Well resolved chromatograms were obtained within 5 min by reversed-phase liquid chromatography with a C8 column as the stationary phase and a pH 4.7 solution containing 0.5% v/v 2-mercaptoethanol and 5% v/v methanol as the mobile phase. The separated mercury compounds were converted to mercury vapors by an in situ nebulizer/vapor generation system for their introduction into ICP. The concentrations of NaBH4 and HNO3 required for vapor generation were also optimized. The method was applied for the speciation of mercury in reference materials NIST SRM 1568a Rice Flour and NIST SRM 1567a Wheat Flour and also rice flour and wheat flour samples purchased locally. The accuracy of the procedure was verified by analyzing the certified reference material NRCC DOLT-3 Dogfish Liver for methyl mercury. Precision between sample replicates was better than 13% for all the determinations. The detection limits of the mercury compounds studied were in the range 0.003-0.006 ng Hg mL(-1) in the injected solutions, which correspond to 0.02-0.06 ng g(-1) in original flour samples. A microwave-assisted extraction procedure was adopted for the extraction of mercury compounds from rice flour, wheat flour, and fish samples using a mobile phase solution.

Microwave-assisted extraction of flavonoids from Radix Astragali

Microwave-assisted extraction (MAE) technique was developed for the fast extraction of flavonoids from Radix Astragali. Several influential parameters of the MAE procedure (microwave power, extraction cycles, ethanol concentration, extraction temperature, irradiation time, and solvent to material ratio) were studied for the optimization of the extraction protocol. The maximum yield of flavonoids with MAE was obtained by dual extraction with 90% ethanol 25 ml/g material at 110 °C for 25 min. No degradation of the flavonoids was observed using the developed extraction protocol. The optimal yield with MAE 1.190 ± 0.042 mg/g were close to that of Soxhlet extracted with methanol for 4 h (1.292 ± 0.033 mg/g) and higher than that of ultrasound assisted extraction with methanol for 2× 30 min and heat reflux extraction with 90% ethanol for 2× 2 h.

Evaluation of microwave-assisted acid extraction procedures for the determination of metal content and potential bioavailability in sediments

Abstract Acid extractions represent a simple and effective tool for the assessment of metal contamination, origin and bioavailability in the aquatic environment. Optimized microwave-assisted procedures utilizing two extractions (8 M HNO 3 and 1 M HCl) were developed. Particular attention was given to the evaluation of efficiency and selectivity of the developed procedures. This involved an examination of the sediment and the extraction residues by Mossbauer spectroscopy and X-ray diffractometry. These instrumental approaches were used to identify the geochemical phases associated with acid decomposition. Microwave digestion with 8 M HNO 3 produced an efficient solubilization of the most important metal-bearing phases and left unaffected only the minerals (quartz, feldspars, muscovite) with a negligible metal content, thus providing a good estimate of the total metal concentrations. The 1 M HCl extraction, despite the limitation due to the incomplete solubilization of pyrite and to the partial dissolution of sheet silicates, represents a simple and effective technique for providing an estimate of the bioavailable metal fraction in sediments. The combined use of the two microwave-assisted acid extractions can provide a rapid and simple approach for the risk assessment of metal-polluted sediments.

Multivariate optimisation of microwave‐assisted extraction of capsaicin from Capsicum frutescens L. and quantitative analysis by 1H‐NMR

A simple and rapid microwave-assisted extraction (MAE) procedure combined with 1H-NMR spectrometry was developed and optimised for the extraction and quantitative determination of capsaicin in Capsicum frutescens. The influence of experimental variables, including irradiation power, extraction temperature and dynamic extraction time before reaching the selected extraction temperature, on the performance of the extraction procedure was systematically studied using a Box-Behnken experimental design followed by a conventional central composite design approach. Statistical treatment of the results together with results from some additional experiments suggested optimum extraction conditions as 120 degrees C and 150 W, for 15 min with acetone as extractant. The optimised MAE method provides extracts that can be analysed quantitatively using 1H-NMR without any preliminary clean-up or derivatisation steps. In the 1H-NMR spectrum of the crude extracts the doublet signal in the delta range 4.349-4.360 ppm was well separated from other resonances in deuterated chloroform. The quantity of the compound was calculated from the relative ratio of the integral value of the target peak to that of a known amount of dimethylformamide as internal standard. In comparison with traditional Soxhlet extraction, the proposed method is less labour-intensive and provides a drastic reduction of extraction time and solvent consumption. In addition, MAE showed higher extraction yield and selectivity, with comparable reproducibility and recovery, relative to both conventional Soxhlet and sonication methods.

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 °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 (MAE) for the determination of polybrominated diphenylethers (PBDEs) in sewage sludge

An efficient microwave-assisted extraction (MAE) method has been developed and evaluated for the quantification of eight major polybrominated diphenylethers (PBDEs) in sewage sludge. The PBDEs were extracted from wet and dry sludge in a microwave extraction unit using a hexane/acetone mixture for 35 min at a controlled temperature of 130 degrees C. The extract was concentrated, cleaned up on a silica gel column, and analyzed by gas chromatography/mass spectrometry (GC/MS) in the negative chemical ionization (NCI) mode. The MAE procedure exhibited higher extraction efficiency, specifically for BDE (brominated diphenylether) 209, than the conventional Soxhlet extraction. The test congeners were clearly separated under specific instrumental operating conditions, at a source temperature of 230 degrees C and a column length of 20 m. The present analytical method showed recovery efficiencies ranging from 80 to 110% when applied to the PBDE-free sludge spiked with eight PBDE congeners. The efficiency of the MAE method was confirmed using sludge obtained from four sewage treatment plants (STPs). The results indicate that BDE 47, 99, and 209 are the most abundant congeners present in these sewage sludges, which is consistent with previous reports.

Microwave-assisted extraction of active pharmaceutical ingredient from solid dosage forms

The microwave assisted extraction (MAE) technique has been evaluated for the extraction of active pharmaceutical ingredients (API) from various solid dosage forms. Using immediate release tablets of Compound A as a model, optimization of the extraction method with regards to extraction solvent composition, extraction time and temperature was briefly discussed. Complete recovery of Compound A was achieved when samples were extracted using acetonitrile as the extraction solvent under microwave heating at a constant cell temperature of 50 °C for 5 min. The optimized MAE method was applied for content uniformity (single tablet extraction) and potency (multiple tablets extraction) assays of release and stability samples of two products of Compound A (5 and 25 mg dose strength) stored at various conditions. To further demonstrate the applicability of MAE, the instrumental extraction conditions (50 °C for 5 min) were adopted for the extraction of montelukast sodium (Singulair ®) from various solid dosage forms using methanol–water (75:25, v/v) as the extraction solvent. The MAE procedure demonstrated an extraction efficiency of 97.4–101.9% label claim with the greatest RSD at 1.4%. The results compare favorably with 97.6–102.3% label claim with the greatest RSD at 2.9% obtained with validated mechanical extraction procedures. The system is affordable, user-friendly and simple to operate and troubleshoot. Rapid extraction process (7 min/run) along with high throughput capacity (up to 23 samples simultaneously) would lead to reduced cycle time and thus increased productivity.

A Microwave-assisted Extraction Method for the Determination of Synthetic Musks in Sewage Sludge

Abstract An efficient microwave-assisted extraction (MAE) procedure has been optimized for the determination of polycyclic and nitro musks in sewage sludge. A centrifuged sludge cake sample (from 1 to 2.5 g ), mixed with 10 g of anhydrous sodium sulfate in a Teflon cell, was extracted with 30 mL of a 1:1 (v/v) mixture of acetone and hexane for 35 min, including a 15-min ramp with a 20-min hold at a controlled temperature of 110°C. After 30 min of cooling, the extract was evaporated and cleaned up on a silica gel column. A concentrated sample extract was then analyzed by gas chromatography/mass spectrometry (GC/MS) in the electron impact mode for the polycyclic musks and in negative ion chemical ionization mode for the nitro musks. This new method has been validated by comparing it to an established accelerated solvent extraction (ASE) method, with method detection limits ranging from 27 to 41 ng/g for the polycyclic musks, and approximately 4 ng/g for the nitro musks. Recoveries of most compounds in spiked samples ranged from 80 to 105%, although the MAE method produced lower recoveries for the nitro musks than the ASE method in archived sludge samples. The results generated by this MAE method were consistent with those prepared by previously reported techniques such as supercritical fluid extraction.

Comparison of extraction procedures for methylmercury determination by a SPME-GC-AFS system

In this study the comparison of three different alkaline extraction techniques carried out with methanolic NaOH followed by phenylation derivatization for the determination of methylmercury in marine fish was performed. The investigated three methods differed in the technique how the extraction assisting energy was introduced to the sample. Namely, closed vessel ultrasonic bath, an open vessel technique using an ultrasonic probe and the microwave assisted extraction procedures were characterized and optimized. Optimum values of 3 h at 75 °C for the ultrasonic bath, 25 min for the ultrasonic probe and 6 min at 60 W for the microwave method were obtained. All three methods were validated using the BCR-464 tuna fish certified reference material.

Optimization of a microwave-assisted extraction method for the analysis of polycyclic aromatic hydrocarbons from fish samples

A microwave-assisted extraction (MAE) procedure has been developed and optimized for the extraction of six regulated polycyclic aromatic hydrocarbons (PAHs) from muscle samples of polluted fish. The procedure involves the simultaneous microwave-assisted extraction of PAHs with n-hexane and the lipids hydrolysis with potassium hydroxide. Experimental design methodology allows a quick and robust optimization of operational parameters such as the extraction time, temperature, and solvent volumes. In these final optimized conditions, the procedure can be applied to a vast range of fat containing fish samples without significant changes, thus enabling its routine use. Recoveries around 90% for the studied compounds benz[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, and indene[1,2,3-cd]pyrene and quantification limits (between 0.07 and 0.53 ng/g dry weight) far below the regulated limits, have been obtained. The procedure is applied to several different fish samples. Further, accuracy validation using NIST SRM 2977 reference material was carried out.

Organochlorine compounds in the marine atmosphere of Singapore

Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were quantified in high-volume air samples collected on polyurethane foam (PUF) over the sea surface of Singapore during the summer monsoon period of 2004. A novel and quality assured microwave-assisted extraction (MAE) procedure for PUF was developed as an alternative to conventional Soxhlet extraction for the analysis of organochlorine compounds (OCs). Average concentrations of ΣPCBs, ΣHCHs and ΣDDTs in air samples were 32, 311 and 8 pg m –3, respectively. Overall, a decline in the ocean atmospheric concentration of DDTs was noted relative to data obtained from the early 1990s, but current data are in a similar range for HCH and PCBs. Levels of OCs in the equatorial atmosphere were compared to equivalent data from temperate regions available in the literature. On a global scale, the levels of DDTs and PCBs in the atmosphere of Singapore are low, but moderate for HCHs.

Optimization of microwave‐assisted extraction for alizarin and purpurin in Rubiaceae plants and its comparison with conventional extraction methods

A simple and rapid microwave-assisted extraction (MAE) procedure was developed and optimized for two common color pigments, alizarin and purpurin, in various samples of Rubiaceae plants. Several variables that can potentially affect the extraction efficiency, namely temperature, methanol concentration in the extractant mixture, time, and solvent volume were optimized by means of a central composite design approach. The results suggest that temperature and methanol concentration in the solvent mixture are statistically the most significant factors. The separation and quantitative determination of the pigments was carried out in less than 6 min by a developed high-performance liquid chromatographic method with UV detection at 250 nm. Under optimum operating conditions, MAE showed significantly higher recoveries than those obtained by the conventional extraction methods (ultrasonic and reflux extraction), ranging from 84 to 94%. In addition, a drastic reduction of the extraction time (20 min versus 6 h) and solvent consumption (20 versus 100 mL) was achieved with a reproducibility (RSDs < 10%) comparable with that provided by the reflux extraction as a reference method.

Single and multiple spike procedures for the determination of butyltin compounds in sediments using isotope dilution GC-ICP-MS

The combined use of single and multiple spike solutions for the determination of butyltin compounds in sediments by species-specific isotope dilution mass spectrometry has been evaluated in this work in order to validate an analytical procedure proposed for routine determinations. For this purpose, a test sediment sample was analysed during the course of an intercomparison exercise using both a single isotope spike solution (a mixture of mono-, di- and tributyltin enriched in 119Sn) and a triple spike solution containing each butyltin species enriched with a different tin isotope. The triple spike methodology (able to correct for interconversion reactions) was employed for the optimisation of the microwave assisted extraction procedure that was subsequently applied for the analysis of the test sediment. The determination of butyltin compounds in the test sediment was performed using both spike solutions under the same extraction conditions. An excellent agreement between the results obtained using both approaches and those provided by all laboratories participating in the intercomparison exercise was obtained, validating in this way the methodologies employed in this work. Uncertainty budgets were calculated for both spiking methodologies. The complexity of the triple spike methodology, in which the simultaneous measurement of nine tin isotope ratios must be carried out, provided additional sources of error in obtaining degradation-corrected concentrations of the three butyltin species. Additionally, uncertainty budgets were obtained also for the calculation of degradation factors F1 (degradation of TBT to DBT) and F2 (degradation of DBT to MBT). The results demonstrated that their uncertainty was independent of the uncertainty of the measurement of the concentration of the butyltin species, both in the spike solution and in the sample, when using a multiple spiking approach, and depended only on the measured isotope ratios and on the uncertainty in the isotopic composition of the spike.