Analysis of phenoxyalkanoic acid herbicides and their phenolic conversion products in soil by microwave assisted solvent extraction and subsequent analysis of extracts by on-line solid-phase extraction-liquid chromatography

A multiresidue method for the determination of phenoxyalkanoic acid herbicides and their phenolic conversion products in soil was developed. The method was based on microwave-assisted solvent extraction (MASE) of soil samples by an aqueous methanolic mixture and subsequent analysis of extracts by automated solid-phase extraction followed by on-line high-performance liquid chromatography and diode array detection. MASE parameters (extraction temperature and time, composition of the extraction mixture and extraction volume) were optimized with respect to analyte recoveries. The method was validated with two types of soils containing 1.5 and 3.5% organic matter, respectively, both types containing fresh and aged residues of sought analytes. Under the selected analytical conditions when soils with fresh residues were analyzed all target analytes were recovered above 80% from the soil containing 1.5% organic matter, while limits of identification at the level of 20-40 ng/g were achieved. From the soil containing 3.5% organic matter the least polar phenolic analytes exhibited slightly reduced recoveries, while identification limits of 30-50 ng/g were achieved. Samples with aged residues exhibited reduced recoveries for some analytes, the reduction amounting up to 6-12% within 1 month of aging period depending on soil organic matter.     

Rapid analysis of pyrethroid insecticides in aquaculture seawater samples via membrane-assisted solvent extraction coupled with gas chromatography-electron capture detection

A simple, efficient, and environmentally friendly membrane-assisted solvent extraction (MASE) method for the extraction and preconcentration of six pyrethroid insecticides from aquaculture seawater samples followed by gas chromatography-electron capture detection (GC-ECD) was successfully proposed. The operating conditions for MASE, such as the extraction solvent, solvent volume, NaCl concentration, stirring rate, extraction time, and temperature, were optimized. Compared to conventional Florisil-solid phase extraction (SPE), higher extraction recoveries (85.9% to 105.9%) of three spiked levels of the six pyrethroid pesticides in aquaculture seawater were obtained using MASE, and the RSD values were lower than 7.9%. The limits of detection (LOD, signal-to-noise ratio (S/N)=3) and quantification (LOQ, S/N = 10) were in the range of 0.037-0.166 and 0.12-0.55 μg L(-1), respectively. The results demonstrate the excellent applicability of the MASE method in analyzing the six pyrethroid pesticides in aqueous samples. The proposed method exhibited a high potential for routine monitoring analysis of pyrethroid insecticides in seawater samples.     

Determination of polybrominated diphenyl ethers in domestic dust by microwave-assisted solvent extraction and gas chromatography-tandem mass spectrometry

In this paper, a rapid and simple method for the analysis of polybrominated diphenyl ethers (PBDEs) in house dust samples based on microwave-assisted solvent extraction (MASE) and gas chromatography-tandem mass spectrometry (GC-MS/MS) is presented. Extraction conditions were optimized using a multifactorial experimental design approach. The use of an aqueous NaOH phase in combination with a non-polar organic phase (hexane) to extract the target analytes from dust allowed an efficient extraction and reduced chromatographic background. The final hexane extracts could be analyzed after a simple one-step cleanup procedure using Florisil. The validation of the method was performed in terms of accuracy, linearity, and repeatability. The limits of detection (LODs) ranged from 0.29 to 0.55 ng/g for all compounds. The target PBDEs were found in several real dust samples collected in urban and rural houses of Northwestern Spain.     

Determination of Organochlorine Pesticides in Sediments from Authie Bay Using Microwave Assisted Solvent Extraction

The aim of this study was to develop an analytical method to determine the organochlorine concentrations in sediments. Combination of Microwave assisted Solvent Extraction (MASE) and capillary gas chromatography with specific detection (electron capture detector) was a viable approach for the determination of pesticides in solid matrixes. In this study, MASE development was focused on the selection of a suitable extraction solvent for all the target analytes. MASE procedure was validated by comparison with conventional methods such as Soxhlet and sonication extraction. The proposed method was then applied to determine the organochlorine insecticides concentrations in samples from Authie Bay (France). Environmental water samples were analysed and five target analytes were detected in concentrations from 0.03 to 0.56 ng/g of dry sediment. These investigations showed the accumulation and the persistency of these products in sediments in spite of the fact they were banned a few decades ago.     

Membrane-assisted solvent extraction of seven phenols combined with large volume injection-gas chromatography-mass spectrometric detection

Membrane-assisted solvent extraction (MASE) was applied for the determination of seven phenols (phenol, 2-chlorophenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol and pentachlorophenol) with log Kow (octanol-water-partition-coefficient) between 1.46 (phenol) and 5.12 (pentachlorophenol) in water. The extraction solvents cyclohexane, ethyl acetate and chloroform were tested and ethyl acetate proved to be the best choice. The optimisation of extraction conditions showed the necessity of adding 5 g of sodium chloride to each aqueous sample to give a saturated solution (333 g/L). The pH-value of the sample was adjusted to 2 in order to convert all compounds into their neutral form. An extraction time of 60 min was found to be optimal. Under these conditions the recovery of phenol, the most polar compound, was 11%. The recoveries of the other analytes ranged between 42% (2-chlorophenol) and 98% (2,4-dichlorophenol). Calibration was performed using large volume injection (100 microL injection volume). At optimised conditions the limits of detection were between 0.01 and 0.6 microg/L and the relative standard deviation (n = 3) was on average about 10%. After the method optimisation with reagent water membrane-assisted solvent extraction was applied to two contaminated ground water samples from the region of Bitterfeld in Saxony-Anhalt, Germany. The results demonstrate the good applicability of membrane-assisted solvent extraction for polar analytes like phenols, without the necessity of derivatisation or a difficult and time-consuming sample preparation.     

Optimization of microwave-assisted solvent extraction for volatile organic acids in tobacco and its comparison with conventional extraction methods

In the present study, a new method using microwave-assisted solvent extraction (MASE) technique followed directly GC analysis was developed for the extraction of volatile organic acids (VOAs) in tobacco. The MASE conditions (heating time, volume of extracting solvent and extraction temperature) were optimized by means of an orthogonal array design (OAD) procedure. The results suggested that extractant, temperature and heating time were statistically the most significant factors. The extracts were directly analyzed with capillary GC operating in splitless-injection mode on an Agilent HP-FFAP capillary column. Under optimum operating conditions, MASE showed significantly better recoveries than those obtained by the conventional extraction method (ultrasonic and reflux extraction), ranging from 90.6% to 103.2%. In addition, a drastic reduction of the extraction time (20 min versus 4 h) and solvent consumption (20 mL versus 100 mL) was achieved with an outstanding reproducibility (CV ≤5%).     

Potential of membrane-assisted solvent extraction for the determination of phosphoric acid triesters in wastewater samples by liquid chromatography-tandem mass spectrometry

A membrane-assisted solvent extraction (MASE) method is presented for the extraction of several non-ionic organophosphorus chemicals from wastewaters samples followed by LC-MS/MS determination. The method was developed for a variety of chlorinated phosphates (trichloroethyl, tichloropropyl) and non-chlorinated phosphates (triphenyl, tributyl) used as flame retardants and for plasticizers such as triethylhexyl and tris-butoxyethyl phosphate. Parameters such as extracting solvent, sample volume and ionic strength, extraction temperature and time were optimized. The final method provides good quantification limits (1-25 ng L(-1)) and linearity (R2>0.9978). Method precision was also good at high concentrations (5% mean RSD at the 500 ng L(-1) level) but decreased at lower concentrations (20% mean RSD at the 20 ng L(-1) level). MASE yields lower matrix effects than SPE in a successive LC-MS/MS analysis of these compounds, avoiding the need for standard addition for quantification. When applied to wastewater samples comparable results were obtained using either MASE with internal standard calibration or SPE with standard addition.     

Comparison of membrane assisted solvent extraction,stir bar sorptive extraction,and solid phase microextraction in analysis of tetramine in food

Three environmentally friendly extraction techniques, membrane assisted solvent extraction (MASE), stir bar sorptive extraction (SBSE), and headspace solid phase microextraction (HS‐SPME), were compared for the direct analysis of the highly toxic rodenticide tetramine in food. The optimized MASE method was applied to seven foods fortified with tetramine and compared to previously reported SBSE and HS‐SPME results. Parameters such as the standard addition linearity (MASE (0.964–0.999), SBSE (0.966–0.999), HS‐SPME (0.955–0.999)), recovery (MASE (12–86%), SBSE (36–130%), HS‐SPME (50–200%)), reproducibility (MASE (3.0–30%), SBSE (4.4–9.6%), HS‐SPME (1–12%)), and LOD (MASE (1.6–6.4 ng/g), SBSE (0.2–2.1 ng/g), HS‐SPME (0.9–4.3 ng/g)) were compared.     

Solid‐based disperser liquid–liquid microextraction for the preconcentration of phthalate esters and di‐(2‐ethylhexyl) adipate followed by gas chromatography with flame ionization detection or mass spectrometry

A new approach for the development of a dispersive liquid–liquid microextraction followed by GC with flame ionization detection was proposed for the determination of phthalate esters and di‐(2‐ethylhexyl) adipate in aqueous samples. In the proposed method, solid and liquid phases were used as the disperser and extractant, respectively, providing a simple and fast mode for the extraction of the analytes into a small volume of an organic solvent. In this method, microliter levels of an extraction solvent was added onto a sugar cube and it was transferred into the aqueous phase containing the analytes. By manual shaking, the sugar was dissolved and the extractant was released into the aqueous phase as very tiny droplets to provide a cloudy solution. Under optimized conditions, the proposed method showed good precision (RSD less than 5.2%), high enrichment factors (266–556), and low LODs (0.09–0.25 μg/L). The method was successfully applied for the determination of the target analytes in different samples, and good recoveries (71–103%) were achieved for the spiked samples. No need for a disperser solvent and higher enrichment factors compared with conventional dispersive liquid–liquid microextraction and low cost and short sample preparation time are other advantages of the method.     

Determination of phenols in water using liquid phase microextraction with back extraction combined with high-performance liquid chromatography.

Liquid phase microextraction with back extraction (LPME/BE) combined with high-performance liquid chromatography (HPLC) was studied for the determination of a variety of phenols in water samples. The target compounds were extracted from 2-ml aqueous sample adjusted to pH 1 (donor solution) through a microliter-size organic solvent phase (400-microl n-hexane), confined inside a small PTFE ring, and finally into a 1-microl basic aqueous acceptor microdrop suspended inthe aforementioned solvent phase from the tip of a microsyringe needle. After extracting for a prescribed time, the microdrop was taken back into the syringe and directly injected into an HPLC for detection. Factors relevant to the extraction procedure were studied. At the optimized extraction conditions, a large enrichment factor (more than 100-fold) can be achieved for most of the phenols within 35 min. The detection limit range was 0.5-2.5 microg/l for different analytes in aqueous samples. The results demonstrate the suitability of the LPME/BE approach to the analysis of polar compounds in aqueous samples.     

Microwave assisted solvent extraction and coupled-column reversed-phase liquid chromatography with UV detection use of an analytical restricted-access-medium column for the efficient multi-residue analysis of acidic pesticides in soils.

A screening method has been developed for the determination of acidic pesticides in various types of soils. Methodology is based on the use of microwave assisted solvent extraction (MASE) for fast and efficient extraction of the analytes from the soils and coupled-column reversed-phase liquid chromatography (LC-LC) with UV detection at 228 nm for the instrumental analysis of uncleaned extracts. Four types of soils, including sand, clay and peat, with a range in organic matter content of 0.3-13% and ten acidic pesticides of different chemical families (bentazone, bromoxynil, metsulfuron-methyl, 2,4-D, MCPA, MCPP, 2,4-DP, 2,4,5-T, 2,4-DB and MCPB) were selected as matrices and analytes, respectively. The method developed included the selection of suitable MASE and LC-LC conditions. The latter consisted of the selection of a 5-microm GFF-II internal surface reversed-phase (ISRP, Pinkerton) analytical column (50 x 4.6 mm, I.D.) as the first column in the RAM-C18 configuration in combination with an optimised linear gradient elution including on-line cleanup of sample extracts and reconditioning of the columns. The method was validated with the analysis of freshly spiked samples and samples with aged residues (120 days). The four types of soils were spiked with the ten acidic pesticides at levels between 20 and 200 microg/kg. Weighted regression of the recovery data showed for most analyte-matrix combinations, including freshly spiked samples and aged residues, that the method provides overall recoveries between 60 and 90% with relative standard deviations of the intra-laboratory reproducibility's between 5 and 25%; LODs were obtained between 5 and 50 microg/kg. Evaluation of the data set with principal component analysis revealed that the parameters (i) increase of organic matter content of the soil samples and (ii) aged residues negatively effect the recovery of the analytes.     

Laser induced-thermal lens spectrometry in combination with dispersive liquid-liquid microextraction for trace analysis

An ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) was developed as a new approach for the extraction of organophosphorus pesticides (OPs) in water samples prior to high-performance liquid chromatography with diode array detection (HPLC-DAD). The use of a surfactant as an emulsifier in the UASEME method could enhance the dispersion of water-immiscible extraction solvent into aqueous phase and is favorable for the mass-transfer of the analytes from aqueous phase to the organic phase. Several variables that affect the extraction efficiency, including the kind and volume of the extraction solvent, the type and concentration of the surfactant, salt addition, ultrasound emulsification time and temperature, were investigated and optimized. Under the optimum experimental conditions, the calibration curve was linear in the concentration range from 1 to 200 ng mL(-1) for the seven OPs (isocarbophos, phosmet, parathion, parathion-methyl, fenitrothion, fonofos and phoxim), with the correlation coefficients (r) varying from 0.9973 to 0.9998. High enrichment factors were achieved ranging from 210 to 242. The established UASEME-HPLC-DAD method has been successfully applied for the determination of the OPs in real water samples. The limits of detection were in the range between 0.1 and 0.3 ng mL(-1). The recoveries of the target analytes over the three spiked concentration levels of the compounds (10, 50, and 100 ng mL(-1), respectively) in rain, reservoir and well water samples were between 83% and 106% with the relative standard deviations varying from 3.3% to 5.6%.     

Ionic‐liquid‐based,manual‐shaking‐ and ultrasound‐assisted,surfactant‐enhanced emulsification microextraction for the determination of three fungicide residues in juice samples

A novel manual‐shaking‐ and ultrasound‐assisted surfactant‐enhanced emulsification microextraction method was developed for the determination of three fungicides in juice samples. In this method, the ionic liquid, 1‐ethyl‐3‐methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, instead of a volatile organic solvent was used as the extraction solvent. The surfactant, NP‐10, was used as an emulsifier to enhance the dispersion of the water‐immiscible ionic liquid into an aqueous phase, which accelerated the mass transfer of the analytes. Organic dispersive solvent typically required in common dispersive liquid–liquid microextraction methods was not necessary. In addition, manual shaking for 15 s before ultrasound to preliminarily mix the extraction solvent and the aqueous sample could greatly shorten the time for dispersing the ionic liquid into aqueous solution by ultrasound irradiation. Several experimental parameters affecting the extraction efficiency, including type and volume of extraction solvent, type and concentration of surfactant, extraction time, and pH, were optimized. Under the optimized conditions, good linearity with the correlation coefficients (γ) higher than 0.9986 and high sensitivity with the limit of detection ranging from 0.4 to 1.6 μg/L were obtained. The average recoveries ranged from 61.4 to 86.0% for spiked juice, with relative standard deviations from 1.8 to 9.7%. The proposed method was demonstrated to be a simple, fast, and efficient method for the analysis of the target fungicides in juice samples.     

Isolation, preconcentration and determination of rhamnolipids in aqueous samples by dispersive liquid-liquid microextraction and liquid chromatography with tandem mass spectrometry

An analytical method based on liquid chromatography-tandem mass spectrometry (LC-MS-MS) was developed for the determination of rhamnolipids. A dispersive liquid-liquid microextraction (DLLME) procedure was used to isolate and concentrate target compounds from aqueous samples collected from surface water, sewage treatment plant effluent and cultivation of microbial culture. Development of the DLLME procedure included optimization of several important parameters such as kind and volume of extracting and dispersing solvents as well as sample pH. Under optimized conditions a two-step extraction with sonication was used. Chloroform was applied as the extracting and acetone as the dispersing solvent. The recoveries of the analytes were 70-87%. Matrix effects investigated for the analytes revealed existence of ionization enhancement for both mono- and dirhamnolipids.     

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.     

High performance liquid chromatography–tandem mass spectrometry for the analysis of 10 pesticides in water: A comparison between membrane-assisted solvent extraction and solid phase extraction

This work describes the application of two sample preparation methods: membrane-assisted solvent extraction (MASE) and solid phase extraction (SPE) in combination with high performance liquid chromatography–tandem mass spectrometry (HPLC–MS–MS) for the determination of 10 pesticides in surface and ground water. Optimal extraction conditions for MASE were 60 min extraction time at 30 °C with a solvent volume of 100 μL toluene. 5 μL of the toluene extract were directly injected in the HPLC–MS–MS system. Concerning SPE, two materials were tested and C18 was superior to Oasis HLB. Complete desorption was ensured by desorbing the SPE (C18) cartridge with 3 mL of an acetonitrile/methanol mixture (1:1). After evaporation, the extract was injected in the analytical system. Analyte breakthrough was not found for the investigated compounds. For both methods, high extraction yields were achieved, in detail 71% (metalaxyl) till 105% (linuron) for MASE and 52% (ethiofencarb) till 77% (prometryne) for SPE (C18). Detection limits were in the low ng/L range for both methods and precision, expressed as the relative standard deviation (RSD) of the peak areas was below 13%. Five real water samples were analyzed applying both extraction methods. The results were in good agreement and standard addition proved that no matrix effects (such as ion suppression) occurred. In this comparison SPE has the potential of larger sensitivity whereas faster analysis and slightly better recoveries were achieved with MASE. MASE shows potential to be a promising alternative to the conventional off-line SPE concerning low to medium polar compounds.     

Temperature‐controlled liquid–liquid microextraction combined with high‐performance liquid chromatography for the simultaneous determination of diazinon and fenitrothion in water and fruit juice samples

A simple, environmentally benign, and rapid method based on temperature‐controlled liquid–liquid microextraction using a deep eutectic solvent was developed for the simultaneous extraction/preconcentration of diazinon and fenitrothion. The method involved the addition of deep eutectic solvent to the aqueous sample followed by heating the mixture in a 75°C water bath until the solvent was completely dissolved in the aqueous phase. Then, the resultant solution was cooled in an ice bath and a cloudy solution was formed. Afterward, the mixture was centrifuged and the enriched deep eutectic solvent phase was analyzed by high‐performance liquid chromatography with ultraviolet detection for quantification of the analytes. The factors affecting the extraction efficiency were optimized. Under the optimized extraction conditions, the limits of detection for diazinon and fenitrothion were 0.3 and 0.15 μg/L, respectively. The calibration curves for diazinon and fenitrothion exhibited linearity in the concentration range of 1–100 and 0.5–100 μg/L, respectively. The relative standard deviations for five replicate measurements at 10.0 μg/L level of analytes were less than 2.8 and 4.5% for intra‐ and interday assays, respectively. The developed method was successfully applied to the determination of diazinon and fenitrothion in water and fruit juice samples.     

Vortex-assisted surfactant-enhanced-emulsification liquid-liquid microextraction

A novel sample pre-treatment technique, based on vortex-assisted surfactant-enhanced-emulsification liquid-liquid microextraction (VSLLME), followed by gas chromatography-flame photometric detection (GC-FPD) has been developed for the determination of seven organophosphorus pesticides (OPPs) in wine and honey samples. In the VSLLME method, the extraction solvent was dispersed into the aqueous samples by the assistance of vortex agitator. Meanwhile, the addition of a surfactant, which was used as an emulsifier, could enhance the speed of the mass-transfer from aqueous samples to the extraction solvent. The main parameters relevant to this method were investigated and the optimum conditions were established: 15 μL chlorobenzene was used as extraction solvent, 0.2 mmol L(-1) Triton X-114 was selected as the surfactant, the extraction time was fixed at 30s, 3% sodium chloride was added and the extraction process was performed under the room temperature. Under the optimum conditions, limits of detections (LODs) were varied between 0.01 and 0.05 μg L(-1). The relative standard deviation (RSD, n=6) ranged from 2.3% and 8.9%. The linearity was obtained by five points in the concentration range of 0.1-50.0 μg L(-1). Correlation coefficients (r) varied from 0.9969 to 0.9991. The enrichment factors (EFs) were in a range of 282-309. Finally, the proposed method has been successfully applied to the determination of target analytes in real samples. The recoveries of the target analytes in wine and honey samples were between 81.2% and 108.0%.     

Membrane-assisted solvent extraction of polychlorinated biphenyls in river water and other matrices combined with large volume injection-gas chromatography-mass spectrometric detection

Membrane-assisted solvent extraction was applied to the determination of polychlorinated biphenyls (PCBs) in aqueous samples. The apparatus of membrane-assisted solvent extraction consisted of a 20 ml headspace vial which was filled with 15 ml of the aqueous sample. The membrane bag was placed into the vial and the extraction took place in an agitator. After extraction, the analytes were transferred into the inlet of a gas chromatograph by large volume injection. A mass-selective detector was used. The whole procedure was fully automated. The work included optimization of the extraction conditions (stirring rate and extraction time) and the influence of matrix effects like salt addition and the presence of organic solvents was studied. Calibration was performed using injection volumes of 100 and 400 microl. Several parameters like linearity and reproducibility of the procedure were determined. At optimized conditions detection limits in the ng/l range were achieved. The effectiveness of the method towards real samples was tested by analyzing river water, white wine and apple juice.     

Determination of linuron and related compounds in soil by microwave-assisted solvent extraction and reversed-phase liquid chromatography with UV detection

The combination of microwave-assisted solvent extraction (MASE) and reversed-phase liquid chromatography (RPLC) with UV detection has been investigated for the efficient determination of phenylurea herbicides in soils involving the single-residue method (SRM) approach (linuron) and the multi-residue method (MRM) approach (monuron, monolinuron, isoproturon, metobromuron, diuron and linuron). Critical parameters of MASE, viz, extraction temperature, water content and extraction solvent were varied in order to optimise recoveries of the analytes while simultaneously minimising co-extraction of soil interferences. The optimised extraction procedure was applied to different types of soil with an organic carbon content of 0.4-16.7%. Besides freshly spiked soil samples, method validation included the analysis of samples with aged residues. A comparative study between the applicability of RPLC-UV without and with the use of column switching for the processing of uncleaned extracts, was carried out. For some of the tested analyte/matrix combinations the one-column approach (LC mode) is feasible. In comparison to LC, coupled-column LC (LC-LC mode) provides high selectivity in single-residue analysis (linuron) and, although less pronounced in multi-residue analysis (all six phenylurea herbicides), the clean-up performance of LC-LC improves both time of analysis and sample throughput. In the MRM approach the developed procedure involving MASE and LC-LC-UV provided acceptable recoveries (range, 80-120%) and RSDs (<12%) at levels of 10 microg/kg (n=9) and 50 microg/kg (n=7), respectively, for most analyte/matrix combinations. Recoveries from aged residue samples spiked at a level of 100 microg/kg (n=7) ranged, depending of the analyte/soil type combination, from 41-113% with RSDs ranging from 1-35%. In the SRM approach the developed LC-LC procedure was applied for the determination of linuron in 28 sandy soil samples collected in a field study. Linuron could be determined in soil with a limit of quantitation of 10 microg/kg.