Rapid method for the determination of organochlorine pesticides and PCBs in fish muscle samples by microwave-assisted extraction and analysis of extracts by GC-ECD

A procedure for the multiresidue determination of organochlorine pesticides and polychlorinated biphenyls in fish muscle samples has been developed. The method is based on the microwave-assisted extraction (MAE) of food samples from an acetonitrile-water (95 + 5, v/v) mixture followed by SPE cleanup of the extracts and analysis by GC with an electron capture detector. MAE operational parameters, such as the extraction solvent, temperature, and time, were optimized with respect to the extraction efficiency of the target compounds from food samples with 10-13% fat content. The chosen extraction technique allows reduction of the solvent consumption and extraction time when compared with methods already used. Acetonitrile is a good extraction solvent for low-fat matrixes (2-20% fat content), such as fish samples, because it does not significantly dissolve the highly polar proteins, salts, and sugars commonly found in food and gives high recoveries of a wide polarity range of analytes. For purification, SPE using LC-Florisil was shown to be sufficient for the removal of coextracted substances. Recoveries > 78% with RSD values < 15% were obtained for all compounds under the selected conditions. Method quantification limits were in the 5-10 microg/kg range. The method was applied to the analysis of samples of herring (Clupea harengus) purchased at the local fish market. The method is rapid and reliable for the determination of organochlorine analytes in fish muscle.     

Determination of organochlorine pesticides and chlorobenzenes in strawberries by using accelerated solvent extraction combined with sorptive enrichment and gas chromatography/mass spectrometry

An analytical scheme for the determination of several organochlorine pesticides like hexachlorocyclohexanes (HCHs) and DDX compounds (p,p'-DDE, p,p'-DDD, and p,p'-DDT) as well as chlorobenzenes in strawberries has been developed. The procedure is based on aqueous accelerated solvent extraction (ASE) followed by solid-phase microextraction (SPME) or stir bar sorptive extraction (SBSE) and subsequent thermodesorption-gas chromatography/mass spectrometry analysis. A 65 microm polydimethylsiloxane/ divinylbenzene fiber was chosen for the SPME experiments. Significant SPME and ASE parameters were optimized using spiked water and strawberry samples. For the ASE of the organochlorine compounds, a water-acetone mixture (90 + 10, v/v) as the extraction solvent, an extraction temperature of 120 degrees C, and 2 cycles of 10 min extraction proved optimal. The developed method was evaluated with respect to precision and limits of detection (LOD). The relative standard deviations of replicate ASE-SPME determinations (n = 5) were in the range of 4-24%. LOD values between 1 and 10 microg/kg were achieved with the exception of DDT and DDE (40 microg/kg). Using SBSE, the LOD of these compounds could be improved (2 and 5 microg/kg). The main advantages of this method are the avoidance of cleanup and concentration procedures as well as the significant reduction of the required volume of organic solvents. The described method was applied to the determination of the pollutants in strawberry samples collected from different allotment gardens in a potentially polluted area, the Bitterfeld-Wolfen region (Germany).     

烟草中有机氯类农药多残留分析前处理方法对比研究

以烟草中有机氯类农药为研究对象,从检出限、回收率、重复性和色谱图4个方面系统比较了机械振荡萃取法、超声波溶剂萃取法、微波辅助萃取法和加速溶剂萃取法4种常用前处理方法。由于加速溶剂萃取法是在高温高压下进行萃取,在提取出残留农药的同时,也提取出更多的干扰物。机械振荡法、超声波溶剂萃取法和微波辅助萃取法各项结果差别较小,其中机械振荡萃取法回收率和重复性最好,但提取时间较长。考虑溶剂消耗和提取时间等方面的因素,微波辅助萃取是较理想的样品前处理方法。     

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.     

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.     

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.     

Extraction of polycyclic aromatic hydrocarbons and organochlorine pesticides from soils: a comparison between Soxhlet extraction, microwave-assisted extraction and accelerated solvent extraction techniques

The methods of simultaneous extraction of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) from soils using Soxhlet extraction, microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) were established, and the extraction efficiencies using the three methods were systemically compared from procedural blank, limits of detection and quantification, method recovery and reproducibility, method chromatogram and other factors. In addition, soils with different total organic carbon contents were used to test the extraction efficiencies of the three methods. The results showed that the values obtained in this study were comparable with the values reported by other studies. In some respects such as method recovery and reproducibility, there were no significant differences among the three methods for the extraction of PAHs and OCPs. In some respects such as procedural blank and limits of detection and quantification, there were significant differences among the three methods. Overall, ASE had the best extraction efficiency compared to MAE and Soxhlet extraction, and the extraction efficiencies of MAE and Soxhlet extraction were comparable to each other depending on the property such as TOC content of the studied soil. Considering other factors such as solvent consumption and extraction time, ASE and MAE are preferable to Soxhlet extraction.     

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     

Application of accelerated solvent extraction coupled with high-performance counter-current chromatography to extraction and online isolation of chemical constituents from Hypericum perforatum L

Accelerated solvent extraction (ASE) coupled with high-performance counter-current chromatography (HPCCC) was successfully used for the extraction and online isolation of five chemical constituents from the plant Hypericum perforatum L. The upper phase of the solvent system of ethyl acetate-methanol-water (5:2:5, v:v:v) was used as both the ASE solvent and the HPCCC stationary phase. Two hydrophobic compounds including 28.4 mg of hyperforin with a HPLC purity of 97.28% and 32.7 mg of adhyperforin with a HPLC purity of 97.81% were isolated. The lower phase of ethyl acetate-methanol-n-butanol-water (5:2:2.5:12, v:v:v:v) was used as both the ASE solvent and CCC stationary phase. Three hydrophilic compounds of 12.7 mg of 3,4,5-O-tricaffeoylquinic acid with a HPLC purity of 98.82%, 15.2 mg of 1,3,5-O-tricaffeoylquinic acid with a HPLC purity of 99.46% and 42.5mg of 3-O-caffeoylquinic acid with a HPLC purity of 96.90%, were obtained in a one-step extraction-separation process with less than 3h from 10.02 g of raw material of H. perforatum. The targeted compounds isolated, collected and purified by HPCCC were analyzed by high performance liquid chromatography (HPLC), the chemical structures of all five compounds above mentioned were identified by UV, MS and NMR.     

Pressurized liquid extraction and microwave-assisted extraction in the determination of organochlorine pesticides in fish muscle samples

This paper describes a comparative study of 2 extraction methods, pressurized liquid extraction (PLE) and microwave-assisted extraction (MAE), for the determination of organochlorine pesticides (OCPs) in fish muscle samples. In both cases, samples were extracted with hexane-acetone (50 + 50), and the extracts were purified by solid-phase extraction using a carbon cartridge as the adsorbent. Pesticides were eluted with hexane-ethyl acetate (80 + 20) and determined by gas chromatography with electron-capture detection. Both methods demonstrated good linearity over the range studied (0.005-0.100 microg/mL). Detection limits ranged from 0.029 to 0.295 mg/kg for PLE and from 0.003 to 0.054 mg/kg for MAE. For most of the pesticides, analytical recoveries with both methods were between 80 and 120%, and the relative standard deviations were < 10%. The proposed methods were shown to be powerful techniques for the extraction of OCPs from fish muscle samples. Although good recovery rates were obtained with both extraction methods, MAE provided advantages with regard to sample handling, cost, analysis time, and solvent consumption. Acceptable validation parameters were obtained although MAE was shown to be more sensitive than PLE.     

Microwave-assisted extraction and mild saponification for determination of organochlorine pesticides in oyster samples

A sample-preparation procedure (extraction and saponification) using microwave energy is proposed for determination of organochlorine pesticides in oyster samples. A Plackett-Burman factorial design has been used to optimize the microwave-assisted extraction and mild saponification on a freeze dried sample spiked with a mixture of aldrin, endrin, dieldrin, heptachlor, heptachorepoxide, isodrin, transnonachlor, p, p'-DDE, and p, p'-DDD. Six variables: solvent volume, extraction time, extraction temperature, amount of acetone (%) in the extractant solvent, amount of sample, and volume of NaOH solution were considered in the optimization process. The results show that the amount of sample is statistically significant for dieldrin, aldrin, p, p'-DDE, heptachlor, and transnonachlor and solvent volume for dieldrin, aldrin, and p, p'-DDE. The volume of NaOH solution is statistically significant for aldrin and p, p'-DDE only. Extraction temperature and extraction time seem to be the main factors determining the efficiency of extraction process for isodrin and p, p'-DDE, respectively. The optimized procedure was compared with conventional Soxhlet extraction.     

A consecutive preparation method based upon accelerated solvent extraction and high‐speed counter‐current chromatography for isolation of aesculin from Cortex fraxinus

A consecutive preparation method based upon accelerated solvent extraction (ASE) coupled with high‐speed counter‐current chromatography (HSCCC) was presented and aesculin was obtained from Cortex fraxinus. The extraction condition of ASE was optimized with response surface methodology; some significant parameters such as the solvent system and its stability, the amount of loading sample in HSCCC were also investigated. The original sample was first extracted with methanol at 105°C and 104 bar for 7 min using ASE, then the extracts were consecutively introduced into the HSCCC system and separated and purified with the same ethyl acetate/n‐butanol/water (7:3:10, v/v/v) solvent system for five times without further exchange and equilibrium. About 3.1 ± 0.2 mg/g in each time and total of 15.4 mg/g aesculin with purity over 95% was isolated from Cortex fraxinus. The results demonstrated that the consecutive preparation method was time and solvent saving and high throughput, it was suitable for isolation of aesculin from Cortex fraxinus, and also has good potential on the separation and purification of effective compounds from natural product.     

Troubleshooting with cell blanks in PLE extraction

The blank extracts obtained from the pressurized liquid extraction (PLE) of a 11 mL empty cell of ASE 200 were analysed by GC-FID and GC-ECD and many interfering peaks were detected, which could difficult the trace analysis of persistent organic pollutants (i.e. polycyclic aromatic hydrocarbons, aliphatic hydrocarbons and organochlorine pesticides). These interfering compounds were identified as phthalates, silicones and organic acids and their sources were established. A solution to this analytical trouble is a previous extraction step of the empty cell under the same conditions optimised for the sample extraction.     

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.     

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.     

High-throughput dynamic microwave-assisted extraction on-line coupled with solid-phase extraction for analysis of nicotine in mushroom

A simple and low-cost high-throughput dynamic microwave-assisted extraction (HTDMAE) device was firstly assembled and validated by the extraction of nicotine in mushroom samples. In this device, a household microwave oven was applied to provide the microwave energy; a vacuum pump was used to deliver the solvent. Compared with traditional dynamic microwave-assisted extraction method, the sample throughput and microwave energy utilization were improved by the HTDMAE, up to 20 samples could be treated simultaneously in 9 min. Taking extraction of nicotine in mushroom sample as an example, a method was established with extraction, separation and enrichment of nicotine in a single step by the device on-line coupled with solid-phase extraction (SPE). Nicotine was first extracted from the mushroom samples with water under the action of microwave energy, and then directly introduced into the SPE column which was packed with cation-exchange resins. Subsequently, the nicotine trapped on the resins was eluted with methanol-ammonia (95:5, v/v) and determined by high-performance liquid chromatography. The limit of detection of nicotine obtained is 5.6 μg kg(-1) in fresh mushroom sample. The recovery of nicotine in mushroom samples is in the range of 87.4-104.0%. The proposed method which significantly reduced the overall analysis time and increased sample throughput should be favored for routine analyse of complex solid sample.     

Separation and purification of furanocoumarins from Toddalia asiatica (L.) Lam. using microwave-assisted extraction coupled with high-speed counter-current chromatography

A method of microwave-assisted extraction coupled with high-speed counter-current chromatography was established for separation and purification of isopimpinellin, pimpinellin and phellopterin from Toddalia asiatica (L.) Lam. The conditions of MAE including the extraction solvent, size of sample, solid/liquid ratio, extraction temperature and extraction time were optimized by a mono-factor test. That is, 2.0 g dried powder of T. asiatica (L.) Lam of 0.30-0.15 mm size was extracted with 20 mL (solid/liquid ratio of 1:10, g/mL) methanol under 50 °C for 1 min. The crude extract was separated and purified by high-speed counter-current chromatography with hexane-ethyl acetate-methanol-water (5:5:5.5:4.5, v/v/v/v) solvent system. 0.85 mg/g of isopimpinellin, 2.55 mg/g of pimpinellin and 0.95 mg/g of phellopterin were obtained from original sample in one-step within 240 min, the purity determined by high performance liquid chromatography was 95.0%, 99.1% and 96.4%, respectively. Their chemical structures were further identified by mass spectroscopy and nuclear magnetic resonance spectroscopy. The results demonstrated that microwave-assisted extraction coupled with high-speed counter-current chromatography was a feasible, economical and efficient technique for rapid extraction, separation and purification of effective compounds from natural products.     

Microwave-assisted solvent elution technique for the extraction of organic pollutants in water

Solid phase extraction (SPE) with appropriate solid sorbents has been commonly used in the routine extraction of organic pollutants in water. The elution of analytes from the solid sorbents normally takes place by organic solvents under an applied vacuum. In this study, a microwave-assisted solvent elution technique was developed for the elution of analytes from C₁₈ membrane disks during microwave irradiation from a microwave extraction system (MES). Several parameters, namely, elution solvent, elution temperature, duration of elution and the volume of solvent which may affect the elution efficiency of microwave-assisted solvent elution (MASE) technique towards organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), phthalate esters (PAEs), organophosphorus pesticides (OPs), fungicides, herbicides and insecticides from the membrane disk were investigated. Good recoveries above 75% were obtained for most of the organic pollutants using the optimum SPE-MASE technique. The effect of sodium chloride and humic acid on the recoveries on the target analytes were also investigated.     

Rapid method for the determination of 16 organochlorine pesticides in sesame seeds by microwave-assisted extraction and analysis of extracts by gas chromatography-mass spectrometry

A method for the multiresidue analysis of 16 organochlorine insecticides in sesame seeds has been developed. The method is based on the microwave-assisted extraction (MAE) of the sesame seeds by the use of a water-acetonitrile mixture followed by Florisil clean-up of the extracts and subsequent analysis by gas chromatography-mass spectrometry (GC/MS) in the selected ion monitoring (SIM) mode. MAE operational parameters (extraction solvent, temperature and time, extractant volume) were optimized with respect to extraction efficiency of the target compounds from sesame seeds with 46% oil content. Recoveries >80% with relative standard deviations (RSD) <12% were obtained for all compounds under the selected parameters. The Florisil clean-up step proved sufficient for the removal of co-extracted substances so that no adverse effect on the chromatographic system was observed. Limit of quantification (LOQ) values were in the range of 5-10 microg/kg. The proposed method was applied in the analysis of sesame seed samples imported to Greece.     

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.