Micro-electron Capture Detector Research Articles

Determination of residual levels of metrafenone in lettuce grown under greenhouse conditions using gas chromatography with a micro-electron capture detector

The current study was carried out to detect metrafenone residues and estimate the half-lives in lettuce grown under greenhouse conditions using gas chromatography with a micro-electron capture detector. Metrafenone was applied in two and three doses (with a 7-day interval) to two different sites in Naju (distance between sites 1 and 2 = 6.5 km) in different seasons (spring and autumn). Samples were extracted with acetone and matrix components were purified using a silica solid-phase extraction (SPE) cartridge. The calibration curve over the concentration range of 0.02–5.0 mg/L was linear with a determination coefficient (R 2) = 0.9993. The limits of detection and quantification were 0.003 and 0.01 mg/L, respectively. Recoveries at two fortification levels (0.1 and 0.5 mg/kg) ranged from 78.5 to 113.3 % with a relative standard deviation <8 %. The calculated half-lives were 2.3 and 2.2 days and 4.9 and 5.0 days for the double and triple doses at sites 1 and 2, respectively. These results suggest that the method is effective and sensitive for the determination of metrafenone residues in field-incurred lettuce samples, and the difference in the reported half-lives is due to seasonal variation.

Thermodynamic and aquatic photodegradation of herbicide butachlor

Thermodynamic and aquatic photodegradation kinetics of a chloroacetamide herbicide (butachlor), subjected to irradiation of ultraviolet light under different temperatures (20–50°C), were investigated. Butachlor residues were determined using gas chromatography coupled with micro-electron capture detector (GC-ECD). The results showed that photochemical reaction of butachlor in water under UV light followed the first order kinetic equation, and the photodegradation efficiency was increased with temperature in the range of 20–50°C. Photodegradation rate constants of butachlor exposed to temperatures of 20, 30, 40, and 50°C were 0.004, 0.007, 0.041, and 0.12 h−1 and their half lives were 175, 100, 17.5, and 5.8 h, respectively. Activation thermodynamic parameters were determined for the degradation process. The reaction activation energy was calculated to be 11.7 kJ mol−1. Results proved that the use of UV irradiation with increasing temperature is a good application to eliminate butachlor from contaminated water.

Deltamethrin Binding to Triatoma infestans (Hemiptera: Reduviidae) Lipoproteins. Analysis by Solvent Bar Microextraction Coupled to Gas Chromatography.

The binding of deltamethrin (DLM) to the hemipteran Triatoma infestans (Klug) hemolymph lipoproteins was evaluated invitro. After DLM incubation with the insect hemolymph, lipoproteins were fractioned by ultracentrifugation. DLM binding was analyzed by a microextractive technique-solvent bar microextraction-a solventless methodology to extract DLM from each lipoprotein fraction. This is a novel use of the technique applied to extract an insecticide from an insect fluid. Capillary gas chromatography with microelectron capture detection was used to detect DLM bound by the T. infestans hemolymph lipoproteins and to identify the preferred DLM carrier. We show that Lp and VHDLp I lipoproteins are mainly responsible for DLM transport in T. infestans, both in DLM-resistant and DLM-susceptible bugs. Our results also indicate that DLM amounts transported are not related to DLM susceptibility.

The toxicity of a new disinfection by-product, 2,2-dichloroacetamide (DCAcAm), on adult zebrafish (Danio rerio) and its occurrence in the chlorinated drinking water

The detection method of 2,2-dichloroacetamide (DCAcAm), a new disinfection by-product (DBP) in chlorinated drinking water, was established using a gas chromatograph coupled with a micro-electron capture detector. The chlorinated water samples were taken from ten drinking water treatment plants around Yangtze River or Taihu Lake in China. The concentration of DCAcAm was detected ranging from 0.5 to 1.8μg/L in the waterworks around Yangtze River, and 1.5–2.6μg/L around Taihu Lake. The toxicity of DCAcAm on adult zebrafish was assessed by investigating the metabolism damage with multiple metabolic biomarkers and the accumulation capability with bio-concentration factor. The results showed that DCAcAm could cause the acute metabolism damage and was easily accumulated in zebrafish, and should be extremely cautioned.

Simultaneous multi-determination and transfer of eight pesticide residues from green tea leaves to infusion using gas chromatography

A method for determining eight pesticide (cyhalothrin, flufenoxuron, fenitrothion, EPN, bifenthrin, difenoconazole, triflumizole, and azoxystrobin) residues in made green tea as well as a tea infusion (under various brewing water temperatures; 60, 80, and 100°C) using gas chromatography (GC) micro-electron capture detector (μECD) was developed and validated. The extraction method adopted the relatively commonly used approach of solid sample hydration, with the green tea hydrated before being extracted through salting out with acetonitrile followed by a cleanup procedure. The analytes were confirmed using GC-coupled to tandem mass spectrometry (GC/MS/MS) with a triple quadrupole. The linearity of the calibration curves yielded determination coefficients (R2) >0.995. Recoveries were carried out using blank samples spiked with all analytes at two levels. The results demonstrated that all pesticides were recovered within the range of 77–116% with a relative standard deviation (RSD) ⩽14%. The quantification limits of 0.015–0.03mg/kg were lower than the maximum residue limits (MRLs) set by the Korea Food and Drug Administration (KFDA) for all analytes (0.05–10mg/kg). The infusion study indicated that cyhalothrin, flufenoxuron, and bifenthrin did not infuse into the tea brew from the made tea. Increases in brewing time resulted in increased transfer of azoxystrobin, fenitrothion, and difenoconazole from the made tea to the brew; however, this was not the case with triflumizole or EPN. We conclude that transfer of pesticides appeared to be dependent on their water solubilities and drinking a cup of tea is recommended to be at a water temperature of 60°C.

A simple and sensitive vortex assisted liquid–liquid microextraction method for the simultaneous determination of haloanisoles and halophenols in wines

A vortex assisted liquid–liquid microextraction (VALLME) method was developed and optimised for the determination of the main compounds that can cause cork taint in wines, 2,4,6-trichloroanisole (TCA), 2,3,4,6-tetrachloroanisole (TeCA), 2,4,6-tribromoanisole (TBA) and pentachloroanisole (PCA); and their corresponding halophenolic precursors. Target compounds were determined by gas chromatography combined with a micro-electron capture detector (GC–µECD) system. Halophenol extraction and derivatisation processes were performed at the same time. To optimise the VALLME method, the extraction solvent was selected. Then, the other parameters of influence, such as volume of extraction solvent and derivatisation agent, salt addition and vortex time were optimised using a central composite design combined with desirability functions. Once the optimal conditions had been determined, the method was validated, showing satisfactory linearity (with correlation coefficients over 0.983), repeatability (below 10.0%) and reproducibility (below 11.2%). Detection limits obtained were lower than the olfactory threshold of the studied compounds, being similar or even lower than previously reported with the advantage of reducing the extraction time. The analysis of real wine samples demonstrated the applicability of the method. To our knowledge, this is the first time that VALLME has been applied for the simultaneous determination of haloanisoles and halophenols in wine.

Determination of Pesticides in the Rhizome of Traditional Chinese Medicines by Gas Chromatography with Electron Capture Detection

A simple and efficient gas chromatography method for the determination of 27 organochlorine and pyrethroid pesticides in traditional Chinese medicine was developed. Pesticide residues were extracted from the samples by oscillation and ultrasound, and purified by gel permeation chromatography and florisil solid phase extraction. The analysis was performed by gas chromatography with micro-electron capture detection. The purification conditions, such as the extraction and elution solvents, extraction methodology, and gel permeation chromatography conditions, were optimized. Traditional Chinese medicines were purified by different methods based on their composition. Under optimized conditions, the calibration graph was linear from 10 to 500 µg/L and the correlation coefficients varied from 0.9958 to 0.9997. The detection limits of these pesticides were between 0.09 and 1.82 µg/kg. The recovery of the pesticides spiked in various samples at four concentrations ranged from 73.2% to 106.4%, with relative standard deviations between 1.0% and 14.0%. This study indicates that the method is useful for determining pesticides in rhizome traditional Chinese medicines.

Anatomical mercury speciation in bay scallops by thio-bearing chelating resin concentration and GC-electron capture detector determination

The highly toxic methyl-, ethyl- and phenylmercury species that may exist in the three main anatomical parts – the adductor muscle, the mantle and the visceral mass – of bay scallops (Argopecten irradias) were quantitatively released by cupric chloride, zinc acetate, sodium chloride and hydrochloric acid (HCl) under ultrasonic extraction. After centrifugation, the mercury species in the supernatant were concentrated by thio (SH)-bearing chelating resins, eluted with HClO4 and HCl and extracted with toluene. Separation was achieved by capillary GC equipped with programmed temperatures, a constant nitrogen flow and detected by a micro-electron capture detector (μECD). Under optimised conditions, the LODs for methyl-, ethyl- and phenylmercury in bay scallop samples were 1.1, 0.65 and 0.80 ng g−1, respectively. The maximum RSD for three replicate determinations of methyl-, ethyl- and phenylmercury in bay scallop samples were 13.7%, 14.0% and 11.2%, respectively. In the concentration range of 4–200 ng g−1 in bay scallop samples, the calibration graphs were linear with correlation coefficients not less than 0.997. Recoveries for spiked samples were in the range of 92.7–103.5% (methylmercury), 87.5–108.3% (ethylmercury) and 91.6–106.0% (phenylmercury), respectively. The method was verified by the determination of methylmercury in a CRM GBW10029 (Total Mercury and Methyl Mercury in Fish Tissue), with results in good agreement with the certified values. Methylmercury – the only existing species in bay scallops – was successfully determined by the method.

Validation of a SPME-GC Method for Azoxystrobin and Pyraclostrobin in Blueberries, and Their Degradation Kinetics

Analytical method for the residues of strobilurins azoxystrobin and pyraclostrobin in blueberries was developed. Fungicide residues were determined by solid-phase microextraction (SPME) cou-pled to gas chromatography with micro-electron capture detector. The effect of pH values and fiber coatings were studied. The SPME fiber coating selected was 100 μm PDMS. The method is selective with adequate precision and high accuracy and sensitivity. Recoveries ranged within the 100% - 106% range for azoxystrobin, and 96% - 106% range for pyraclostrobin; and detection and quantification limits were 2.0 and 6.0 μg/kg for azoxystrobin, and 26.0 and 86.0 μg/kg for py-raclostrobin, respectively. Statistical parameters indicated the occurrence of matrix effect; con-sequently calibration was performed on spiked samples. Degradation of azoxystrobin and pyra-clostrobin was studied in blueberry fields located in Concordia, Argentina, with fruits from Emerald and Jewel varieties. The degradation of these fungicides in both blueberry varieties studied followed a first order rate kinetics, and the half-life for azoxystrobin was 11.6 and 17.8 days for Emerald and Jewel cultivars; and for pyraclostrobin was 5.5 and 8.0 days, respectively.

Determination of Triazolam and Midazolam in Human Plasma Using Gas Chromatography with Microelectron Capture Detection for Clinical Application

A method for the simple and reliable determination of triazolam and midazolam in human plasma using gas chromatography with microelectron capture detection has been developed. Samples (0.5 mL of plasma) were prepared using a simple solvent extraction with 3% isoamyl alcohol/benzene in the presence of NaOH. Two microlitres of the extract were injected onto the capillary column ((5%-phenyl)-methylpolysiloxane). The method was found to be valid in terms of selectivity, linearity, precision, accuracy, and recovery over the concentration range of 0.2 to 20 ng/mL for triazolam, and from 0.5 to 200 ng/mL for midazolam, respectively. Intra- and inter-day precisions determined at three concentrations were from 4.1 to 9.3% for triazolam and from 2.9 to 13.0% for midazolam. The accuracies were within 17.7% for triazolam and within 13.0% for midazolam. This proposed method was successfully applied to a pharmacokinetic study of triazolam or midazolam in healthy volunteers.

Comprehensive Two-dimensional Gas Chromatography with Micro-electron Capture Detector for Analysis of Toxaphene Congeners in Soil

A comprehensive two dimensional gas chromatography coupled with micro-electron capture detector(GC×GC-μECD) method for the simultaneous analysis of 23 congeners of toxaphene in soil has been developed and validated.A DB-XLB column(20 m×0.25 mm×0.25 μm) was chosen as the column for the first dimension,and a BPX-50 column(2 m×0.1 mm×0.1 μm) was chosen as the column for the second dimension.The matrix-matched external standard calibration curves were used for quantitative analysis.The established method showed good linearity with correlation coefficients(r2) higher than 0.99 in the concentration range of 1-200 μg/L.Limits of detection ranged from 0.039 to 0.482μg/L for individual congeners.The relative standard deviations(RSD) of all 23 toxaphene congeners in matrix spiked samples were below 30%(n=5),and recoveries ranged from 55% to 115%.For validation,the developed method was applied to the determination of toxaphene in a soil sample.

Novel solvent-free microwave-assisted extraction coupled with low-density solvent-based in-tube ultrasound-assisted emulsification microextraction for the fast analysis of organophosphorus pesticides in soils

A novel and rapid solventless microwave-assisted extraction coupled with low-density solvent-based in-tube ultrasound-assisted emulsification microextraction has been developed for the efficient determination of nine organophosphorus pesticides in soils by GC analysis with microelectron capture detection. A specially designed, homemade glass tube inbuilt with a scaled capillary tube was used as an extraction device to collect and measure the separated extractant phase easily. Parameters affecting the efficiencies of the developed method were thoroughly investigated. From experimental results, the following conditions were selected for the extraction of organophosphorus pesticides from 1.0 g of soil sample to 5 mL of aqueous solution under 226 W of microwave irradiation for 2.5 min followed by ultrasound-assisted emulsification microextraction with 20 μL toluene for 30 s and then centrifugation at 3200 rpm for 3 min. Detections were linear in the range of 0.25-10 ng/g with detection limits between 0.04 and 0.13 ng/g for all target analytes. The applicability of the method to real samples was assessed on agricultural contaminated soils and the recoveries ranged between 91.4 and 101.3%. Compared to other methods, the present method was shown to be highly competitive in terms of sensitivity, cost, eco-friendly nature, and analysis speed.

Comparative study on disappearance trends of captan and trifloxystrobin residues on fruit and apple tree leaves using internal normalisation method

Supervised field trials were carried out in a commercial orchard in 2011. The purpose of the study was to assess the usefulness of the comparative method to examine the mechanism of disappearance of pesticide residues. Captan and trifloxystrobin residues were determined with the use of gas chromatograph equipped with a micro-electron capture detector. Disappearance trends of captan and trifloxystrobin residues in fruit and leaves were estimated using the method of internal normalisation, and based on that, the courses of concentration changes of these substances on fruit and leaves and the amount of these substances in one apple were established. The initial deposits of trifloxystrobin on leaves and fruits dropped by 50% within 8 and 4 days after treatment, respectively, in both varieties, whereas captan residues dropped by 50% within 29 days in leaves and 7 days in apples of the Olive Yellow varieties.

Miniaturized selective pressurized liquid extraction of polychlorinated biphenyls and polybrominated diphenyl ethers from feedstuffs

A new miniaturized pressurized liquid extraction (PLE) with in-cell purification method has been developed for the simultaneous extraction of endogenous prioritary and toxic polychlorinated biphenyls (PCBs) and environmentally relevant tri- to deca-brominated diphenyl ether (PBDE) congeners from different feed matrices. Parameters affecting the efficiency of the selective PLE process, such as sorbent:matrix ratio, volume and nature of the extraction solvent, PLE working mode, extraction time and temperature, and amount of co-sorbents, were optimized. n-Hexane and n-hexane:dichloromethane (1:1, v/v) were used as extraction solvents. 8-mL of organic solvents and 3.5g of sorbents sufficed for complete sample treatment. Only 0.25g of feed sample were required for accurate determination of the endogenous PCBs studied using gas chromatography with a micro-electron capture detector (GC-μECD) during method development, and for PBDE analysis using either GC-μECD or gas chromatography with negative chemical ionization-quadrupole mass spectrometry (GC–NCI-qMS). Gas chromatography coupled to ion trap detection working in tandem mode, GC-ITD (MS/MS), was used for final PCB confirmation. Additional purification of the sample extracts was not required. The performance of the complete PLE-based method was evaluated at two spiking levels, 0.4 and 4ng/g wet weight. Recoveries in the range 60–120% were obtained for PCBs, while those of PBDEs ranged from 86% to 114% for most of the target analytes. The relative standard deviations were in general lower than 20%. The optimized procedure was applied to the determination of the investigated PCBs and PBDEs in a variety of feed samples.

Distributions, sources, and ecological risks of hexachlorocyclohexanes in the sediments from Haihe Plain, Northern China

The levels of hexachlorocyclohexanes (HCHs) in the sediments from Haihe Plain, China, were measured by a gas chromatograph with a (63)Ni microelectron capture detector. The spatial distributions, possible sources, and potential ecological risks of these compounds were analyzed. The residual level of total HCHs was 33.84 ± 173.37 ng g(-1) dry weight (d.w.) with ranges of 0.13 ~ 1,107.41 ng g(-1) d.w. Much higher ΣHCH contents were found in the lower reaches of some rivers and in the mouth of the main stream receiving tributaries. The predominance of β-HCH (36%) in the sediments was similar to that in the soils from Haihe Plain. The high percentages of γ-HCH (23-41%) could be detected at 25% of the sampling sites in the seven river systems. There were statistically significant positive relationships between the contents of HCHs and total organic carbon. Lindane was identified as the primary source of HCHs in the sediments, and it seemed that recent illegal lindane inputs still existed in some areas in Haihe Plain, as indicated by the α-/γ-HCH and β-/(α + γ)-HCH ratios. Severe potential ecological risks of γ-HCH to benthic organisms at some sampling sites were found based on the consensus-based sediment quality guidelines.

Method development and validation for boscalid in blueberries by solid-phase microextraction gas chromatography, and their degradation kinetics

Analytical method for the residues of boscalid in blueberries was developed. Fungicide residues were determined by solid-phase microextraction (SPME) coupled to gas chromatography with micro-electron capture (μ-ECD) detector. The effect of pH values and fiber coatings were studied. The SPME fiber coating selected was 100μm PDMS. The method is selective with adequate precision and high accuracy and sensitivity. Recoveries ranged within the 98–104% range, and detection and quantification limits were 1.33 and 4.42μg/kg, respectively. Statistical parameters indicated the occurrence of matrix effect; consequently calibration was performed on spiked samples. Degradation of boscalid was studied in a blueberry field located in Concordia, Argentina, with fruits from Emerald and Jewel varieties. The degradation of boscalid in both blueberry varieties studied followed a first order rate kinetics and the half-life for boscalid was 5.3 and 6.3days for Emerald and Jewel cultivars, respectively.

Dispersive liquid–liquid microextraction with non-halogenated extractants for trihalomethanes determination in tap and swimming pool water

An effective, low solvent consumption, reduced cost and high throughput sample preparation method for the determination of four trihalomethanes (THMs) in tap and swimming pool water samples is presented. THMs extraction and concentration were performed by dispersive liquid–liquid microextraction (DLLME), based on the use of non-halogenated and low volatile solvents as extractants. Analytes were further determined by gas chromatography with micro-electron capture detection (GC-microECD). Under optimized conditions, the proposed method uses 18mL volume samples, 0.7mL of acetone (dispersant) and 0.05mL of 1-undecanol (extractant). Achieved enrichment factors (EFs) varied from 67 to 104 times, the limits of quantification (LOQs) stayed between 0.05 and 1.3ngmL−1, and an excellent linearity was noticed up to 100ngmL−1. Relative recoveries, measured for spiked aliquots of tap and swimming pool water samples, remained between 79% and 113%, with associated standard deviations below 12%. The applicability of the developed methodology was demonstrated with chlorinated water samples analysis. As regards tap water samples, the sum of THMs concentrations remained under the limit fixed by the European Union (100ngmL−1); however, some samples contained levels close to 80ngmL−1, the maximum allowable concentration established by the United States Environmental Protection Agency (EPA).

Distributions, sources, and ecological risks of DDT-related contaminants in water, suspended particulate matter, and sediments from Haihe Plain, Northern China

The residual levels of dichlorodiphenyltrichloroethane (DDT) and its metabolites (DDXs, including p,p'-DDT, DDD, and DDE) in water, suspended particulate matter (SPM), and sediments from major rivers, lakes, and reservoirs in Haihe Plain were measured with a gas chromatograph equipped with a (63)Ni microelectron capture detector. In the fall of 2004, the contents of the total DDXs in the water and SPM were 0.29 ± 0.69 ng L(-1) and 423.13 ± 577.85 ng g(-1) dry wt., respectively. In the spring of 2005, the total DDXs were 0.36 ± 0.91 ng L(-1) for water and 35.93 ± 62.65 ng g(-1) dry wt. for SPM. The average concentration of DDXs for sediments was 7.10 ± 7.57 ng g(-1) dry wt. during the two seasons. The Eastern-Hebei-Province Coastland River System was the most polluted, which was mainly attributable to the extensive use of DDT pesticide and dicofol in that system. Recent DDT inputs still occur in some regions, as indicated by DDT/(DDD + DDE) > 1 at 29-36 % of the sites for water and 55-61 % of the sites for SPM. The potential ecological risks of DDT in the water were assessed using a species sensitivity distribution model. Only shrimp and crabs were found to have potentially affected fraction values of 1.63 × 10(-3) to 2.27 × 10(-4), with probabilities beyond the hazardous concentration for 5 % of species (HC5) values of 1.90-2.56 %, suggesting only slight risks. DDXs in the sediments of some sites were also of potential risk to benthic organism based on consensus-based sediment quality guidelines.

Residues and ecological risks of organochlorine pesticides in Lake Small Baiyangdian, North China

The levels of hexachlorocyclohexane (HCH) and dichloro-diphenyl-trichloroethane (DDT) in the water, suspended particulate matter (SPM), and sediments from Lake Small Baiyangdian were measured by gas chromatograph with a (63)Ni microelectron capture detector. The residual levels of the total HCHs in the water, SPM, and sediments were 1.59 ± 2.24 ng L(-1), 25.42 ± 1.72 ng g(-1) dw (dry weight), and 0.86 ± 1.44 ng g(-1) dw, respectively. DDTs were not detected in the water samples. The concentrations of total DDTs were 158.79 ± 1.67 ng g(-1) dw in SPM and 0.46 ± 1.97 ng g(-1) dw in the sediments. Compared to other areas in China and abroad, the levels of residual HCH and DDT were relatively low in the water and sediments, but they were moderate to high in the SPM. Organic carbon partition coefficient values for HCH in this study were higher than previously published values and may reflect new input in this area. The residual HCHs in this area could be derived from a mixture of technical HCH and lindane because ongoing lindane use may be occurring. DDT in the majority of the study area was primarily attributed to historical discharge, but some regions may be receiving new input. The ecological risks of γ-HCH in the water were very low according to species sensitivity distribution models. The concentrations of HCH and DDT in the sediments from the study area did not exceed the sediment quality guidelines, which indicate little risk for benthic organisms.

Polybrominated diphenyl ethers (PBDEs) and 2,2′,4,4′,5,5′-hexabromobiphenyl (BB-153) in landfill leachate in Cape Town, South Africa

An assessment of the concentrations of selected polybrominated diphenyl ether (PBDE) congeners as well as BB 153 in leachate samples collected from three landfill sites within the city of Cape Town was conducted. A liquid-liquid extraction technique was employed for the isolation of all the target compounds from the leachate samples. Extracts obtained were further subjected to multi-layer column chromatography employing different forms of silica gel. The prepared samples were analysed using a high capillary gas chromatograph equipped with a micro-electron capture detector (GC-μECD). The overall mean concentrations of the total PBDEs, including BDE 209 ranged between 5.65 and 2,240, 0.28-20.5 and 1.66-1,170 ng/l for Bellville, Coastal Park, and Vissershok landfill sites, respectively. The mean concentrations of BB 153, which were generally low in most of the samples analysed, were 70.4, 7.14 and 8.16 ng/l for Bellville, Coastal Park and Vissershok sites, respectively. The influence of precipitation on the characteristics and quantity of leachate produced from the landfill sites investigated was most pronounced during the August/September sampling regime. Generally, the trend observed in this study clearly indicated a wide variation in the levels of these contaminants in all the landfill sites studied from one sampling period to the other. However, the principal component analysis revealed that the release of these contaminants might be associated with two or three possible sources. This study further confirmed the relevance of landfill leachate as an important source of PBDE contamination of the environment, especially the groundwater and surface water sources.