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     

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.     

Dispersive solid-phase extraction clean up combined with Soxhlet extraction for the determination of 16 PAHs in soil samples by GC-MS

Dichloromethane soil samples extracts were prepared using Soxhlet extraction technique, and after clean-up step, gas chromatography-mass spectrometry analysis of 16 priority polycyclic aromatic hydrocarbons (PAHs) was carried out. A comparison of dispersive solid-phase extraction (dSPE) and column chromatography (cC), as clean-up techniques, was evaluated. Six different sorbents (silica, diatomaceous earth, primary–secondary amine, C18, clinoptilolite and florisil) were tested as dispersive clean-up sorbents versus activated silica and alumina for cC. Best results for three concentration levels among dSPE were obtained using diatomaceous earth, with recovery values in the range of 75–112% for 13 of 16 analysed compounds, while cC recoveries were in the range of 75–111% for all analysed PAHs. Analysis of 12 soil samples from urban area of Ni? (Serbia) singled out acenaphthene as the most abundant compound.     

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.     

Comprehensive comparison of classic Soxhlet extraction with Soxtec extraction, ultrasonication extraction, supercritical fluid extraction, microwave assisted extraction and accelerated solvent extraction for the determination of polychlorinated biphenyls in soil

This paper compares the extraction effectiveness of six different commonly applied extraction techniques for the determination of PCBs in soil. The techniques included are Soxhlet, Soxtec, ultrasonication extraction, supercritical fluid extraction, microwave-assisted extraction and accelerated solvent extraction. For none of the techniques were the extraction conditions optimized, but instead the extraction parameters were based on the experience from previous successful investigation published by a number of research groups worldwide. In general, all extraction techniques were capable of producing accurate data for one native PCB contaminated soil diluted with another soil sample to obtain two concentration levels. It could therefore be concluded that any of the investigated techniques can be used with success if the extraction conditions applied are chosen wisely.     

Comparison of accelerated solvent extraction with microwave-assisted extraction and Soxhlet for the extraction of chlorinated biphenyls in soil samples

The extraction and determination of chlorinated biphenyls (CBs) in soils and solid wastes is an ongoing subject of study. This is an overview article that compares the microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) techniques. The extraction of CBs by ASE has been optimised taking into account the variation of pressure, temperature and extraction time by means of experimental design and the Simplex approach. The recoveries obtained under the optimum conditions are compared and discussed with those obtained from MAE and Soxhlet extractions.     

Optimization of microwave-assisted extraction of hydrocarbons in marine sediments: comparison with the Soxhlet extraction method

Microwave energy was applied to extract polycyclic aromatic hydrocarbons (PAHs) and linear aliphatic hydrocarbons (LAHs) from marine sediments. The influence of experimental conditions, such as different extracting solvents and mixtures, microwave power, irradiation time and number of samples extracted per run has been tested using real marine sediment samples; volume of the solvent, sample quantity and matrix effects were also evaluated. The yield of extracted compounds obtained by microwave irradiation was compared with that obtained using the traditional Soxhlet extraction. The best results were achieved with a mixture of acetone and hexane ¶(1?:?1), and recoveries ranged from 92 to 106%. The extraction time is dependent on the irradiation power and the number of samples extracted per run, so when the irradiation power was set to 500 W, the extraction times varied from 6 min for 1 sample to 18 min for 8 samples. Analytical determinations were carried out by high-performance liquid chromatography (HPLC) with an ultraviolet-visible photodiode-array detector for PAHs and gas chromatography (GC) using a FID detector for LAHs. To test the accuracy of the microwave-assisted extraction (MAE) technique, optimized methodology was applied to the analysis of standard reference material (SRM 1941), obtaining acceptable results.     

Optimization of microwave-assisted extraction of hydrocarbons in marine sediments: comparison with the Soxhlet extraction method

Microwave energy was applied to extract polycyclic aromatic hydrocarbons (PAHs) and linear aliphatic hydrocarbons (LAHs) from marine sediments. The influence of experimental conditions, such as different extracting solvents and mixtures, microwave power, irradiation time and number of samples extracted per run has been tested using real marine sediment samples; volume of the solvent, sample quantity and matrix effects were also evaluated. The yield of extracted compounds obtained by microwave irradiation was compared with that obtained using the traditional Soxhlet extraction. The best results were achieved with a mixture of acetone and hexane (1:1), and recoveries ranged from 92 to 106%. The extraction time is dependent on the irradiation power and the number of samples extracted per run, so when the irradiation power was set to 500 W, the extraction times varied from 6 min for 1 sample to 18 min for 8 samples. Analytical determinations were carried out by high-performance liquid chromatography (HPLC) with an ultraviolet-visible photodiode-array detector for PAHs and gas chromatography (GC) using a FID detector for LAHs. To test the accuracy of the microwave-assisted extraction (MAE) technique, optimized methodology was applied to the analysis of standard reference material (SRM 1941), obtaining acceptable results.     

A comparison of accelerated solvent extraction,Soxhlet extraction,and ultrasonic-assisted extraction for analysis of terpenoids and sterols in tobacco

The performance of accelerated solvent extraction in the analysis of terpenoids and sterols in tobacco samples was investigated and compared with those of Soxhlet extraction and ultrasonically assisted extraction with respect to yield, extraction time, reproducibility and solvent consumption. The results indicate that although the highest yield was achieved by Soxhlet extraction, ASE appears to be a promising alternative to classical methods since it is faster and uses less solvent, especially when applied to the investigation of large batch tobacco samples. However, Soxhlet extraction is still the preferred method for analyzing sterols since it gives a higher extraction efficiency than other methods.     

Determination of hexabromocyclododecane diastereoisomers in Sargassum fusiforme and comparison of the extraction efficiency of ultrasonication, microwave-assisted extraction, Soxhlet extraction and pressurised liquid extraction

The concentrations of hexabromocyclododecanes (HBCD) in Sargassum fusiforme, the common Chinese edible seaweed, were investigated by LC‐MS/MS. For the recovery of HBCD, the efficiency levels of ultrasonic‐assisted extraction, microwave‐assisted extraction, Soxhlet extraction and pressurised liquid extraction were compared under different conditions. Pressurised liquid extraction and ultrasonic‐assisted extraction resulted in complete extraction of HBCD (92.7–102.5% recovery). Microwave‐assisted extraction and Soxhlet extraction, on the other hand, offered relatively low extraction recoveries (82.1–90.6%). The instrumental LODs on columns in this study were 1.0, 0.3 and 0.7 ng/g for α‐HBCD, β‐HBCD and γ‐HBCD, respectively. Because of its accuracy, this straightforward method is particularly suitable for routine HBCD analysis.     

Headspace-mass spectrometry determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers in soil samples using chemometrics

A simple and fast method has been developed for the determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers (BTEX) in soils. Samples were introduced in 10 mL standard glass vials of a headspace (HS) autosampler together with 150 μL of 2,6,10,14-tetramethylpentadecane, heated at 90 °C for 10 min and introduced in the mass spectrometer by using a transfer line heated at 250 °C as interface. The volatile fraction of samples was directly introduced into the source of the mass spectrometer which was scanned from m/z 75 to 110. A partial least squares (PLS) multivariate calibration approach based on a classical 3³ calibration model was build with mixtures of benzene, toluene and o-xylene in 2,6,10,14-tetramethylpentadecane for BTEX determination. Results obtained for BTEX analysis by HS-MS in different types of soil samples were comparables to those obtained by the reference HS-GC-MS procedure. So, the developed procedure allowed a fast identification and prediction of BTEX present in the samples without a prior chromatographic separation.     

Application of ultrasound-assisted extraction to the determination of contaminants in food and soil samples

The application of ultrasound-assisted extraction (UAE) to the sample preparation of environmental and food samples has increased in the last years. This technique has been used in the development of methods for the analysis of numerous contaminants, including organic compounds (pesticides, pharmaceuticals, polycyclic aromatic hydrocarbons, polyhalogenated flame retardants, etc.) and heavy metals. The aim of this work is to review the application of this extraction procedure to the analysis of contaminants in food and soil and the comparison of its use with other well-established extraction procedures. The advantages and disadvantages of this technique together with the possibility of coupling UAE with other analytical techniques will be also discussed.     

Luminescence determination of benzoquinoline isomers in complex samples

The room-temperature phosphorescence (r.t.p.) and fluorescence spectra of benzoquinoline isomers are investigated. The isomers can be resolved into the linear or angular subgroups on the basis of their fluorescence and r.t.p. spectra by using conventional fixed excitation. Second-derivative and synchronous scanning techniques can be combined to improve the selectivity of the r.t.p. and fluorescence methods. These simple luminescence techniques were used to estimate three benzoquinoline isomers in a coal tar fraction. Direct analysis of this complex sample allowed acridine to be estimated and upper limits to be provided for benzo(h)quinoline and phenanthridine; the presence of three other isomers was not detected. Comparative studies with data obtained by high-performance liquid chromatography are reported.     

Optimization of matrix solid-phase dispersion conditions for organic fungicides determination in soil samples

A simplified sample preparation method, based on the matrix solid-phase dispersion technique, is proposed for the sensitive determination of 15 organic fungicides in vineyard soils by gas chromatography-mass spectrometry (GC-MS). Under final working conditions, sieved samples (0.5 g) were blended and dispersed with 2 g of C18 and transferred to a polypropylene syringe containing 1 g of diatomaceous earth. Analytes were recovered using 10 mL of ethyl acetate, this extract was concentrated to 1 mL and fungicides determined by GC-MS, without additional cleanup. The method provided recoveries in the range from 74 to 122% for soils with total carbon contents up to 5.5% and it allowed the use of external standard as quantification technique. Inter-day precision, given as relative standard deviations, stayed between 3 and 13%, and the limits of quantification were comprised between 0.6 and 15 ng g(-1). Several fungicides were found in the top layer of vineyard soils with the highest detection frequency and maximum concentration corresponding to iprovalicarb. Some real samples were also submitted to pressurized liquid extraction. Measured concentrations were in excellent agreement with those obtained by matrix solid-phase dispersion, which reinforces the accuracy of the latter methodology.     

Optimisation of microwave-assisted extraction for the determination of nonylphenols and phthalate esters in sediment samples and comparison with pressurised solvent extraction

Microwave-assisted extraction (MAE) of nonylphenols (NP), nonylphenol mono- and diethoxylates (NP1EO and NP2EO, respectively) and phthalate esters was optimised using an experimental design approach. A D-optimal mixture design was used to optimise the pressure inside the extraction vessel (110-207 kPa), the extraction time (5-25 min) and the extraction solvent (methanol, acetone or n-hexane) or the solvent mixture for the microwave-assisted extraction. Percentage of microwave power (80%) and solvent volume (15 ml) were fixed in all the experiments. As a consequence, the optimum extraction of these compounds was carried out at an intermediate pressure (159 kPa) with pure methanol and during 15 min. Moreover, solid phase extraction was also optimised for the clean-up of the extracts and C-18, LiChrolut^® and Oasis^® cartridges were studied in order to obtain the best recoveries of the compounds of interest. The highest recoveries were obtained with LiChrolut^® cartridges after the elution with ethyl acetate. The cleaned extracts were analysed in a gas chromatograph with mass spectrometric detection and in a liquid chromatograph with diode array and fluorescence detection (HPLC-DAD-UV-FLD). The same sediment was also extracted twice in order to check that an exhaustive extraction of the analytes had occurred. Finally, the optimised extraction method was compared with pressurised solvent extraction (PSE), using an estuarine sediment sample.     

Combination of microwave assisted micellar extraction and liquid chromatography for the determination of organophosphorous pesticides in soil samples

A new methodology based on the microwave assisted micellar extraction (MAME) technique has been optimised, using soil samples, to extract and determine a mixture of the eight organophosphorous pesticides mainly used in agriculture. The pesticides under study have been extracted using the non-ionic surfactants polyoxyethylene 10 lauryl ether (POLE) and oligoethylene glycol monoalkyl ether (Genapol X-080). The optimal extraction variables, such as surfactant concentration, pH, radiation time and microwave power were determined for each surfactant. The results show the advantage of using POLE instead of Genapol X-080 for the extraction of the organophosphorus pesticides with recoveries higher than 70% for most of the compounds and relative standard deviations (RSD) below 2.6%. This method was successfully applied to fresh samples as well as to aged samples for the analysis of soils with different characteristics and compared with the traditional Soxhlet technique.     

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 °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 °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.