Thermionic Specific Detection Research Articles

Catalytic degradation of propetamphos and azamethiphos using silver ion.

In this study, the degradation of two organophosphate pesticides, namely, propetamphos and azamethiphos, in the presence of Ag+ at different mole ratios was investigated. Moreover, the kinetic and degradation pathways of both chemicals in the range of 0-60min were explored. Gas chromatography equipped with a thermionic specific detector was used to investigate the pesticide degradation kinetics and mechanism. The results show that the degradation rate of both pesticides follows first-order kinetic. The first-order rate constant and the half-life of reaction were in the range of 0.002-0.143min-1, 187-2.1min, and 0.005-0.164min-1 and 60-1.8min, for propetamphos and azamethiphos, respectively, at ambient temperature (25 ºC). Because group containing sulfur atom is a better leaving group than group containing nitrogen, the rate of degradation of azamethiphos is higher than propetamphos. In a higher mole ratio of Ag+ to pesticides, the degradation rate was increased, and it is possible to predict the rate of degradation of pesticides according to the chemical composition of leaving group.

Residual fate of fenazaquin (10EC) in apple fruit and soil

ObjectivesA field trial was carried out in Kashmir valley to determine the persistence of fenazaquin 10EC (Magister) in Red Delicious variety of apple at recommended (0.004%) and double the recommended (0.008%) application rates. MethodsThe spray was conducted one month prior to harvest. The plants treated with simple tap water were treated as control. Samples were collected at 0, 3, 7, 10, 15, 20 days and harvest. The procedure followed for extraction and cleanup was that of Luke et al. (1985) modified by Sharma (2007) and the final analysis was carried out on a Varian 450 (Walnut Creek, CA, USA) gas chromatograph (GLC) equipped with Thermionic Specific detector (TSD). ResultsAfter computation of data, the initial deposit was recorded as 3.18 ± 0.03 μg g − 1 and 6.98 ± 0.08 μg g − 1 at two concentrations, respectively. Fenazaquin (0.004%) dissipated to 96.91 per cent in 20 days after application and was not detectable beyond this period. Fenazaquin (0.008%) however, persisted upto 30 days recording 95.84 per cent dissipation at that time. ConclusionsThe progressive dissipation of fenazaquin (0.004%) and fenazaquin (0.008%) residues down to their tolerance limits suggested a waiting period of 18.55 and 30.49 days with a half-life period of 3.62 and 4.12 days, respectively. The terminal residue of fenazaquin at the lower rate was below maximum residue limit (MRL) set by European Union, however above MRL at the higher rate.

Validation and application of a multi-residue method, using accelerated solvent extraction followed by gas chromatography, for pesticides quantification in soil.

A multi-residue method was developed to determine different types of pesticides in soils. An extraction with pressure and temperature, through accelerated solvent extraction (dichloromethane:acetone, 50:50, v/v). The pesticides were determined by gas chromatography with several selective detectors: electron capture detector, pulsed flame photometric detector and thermionic specific detector. The following parameters were determined: limit of detection, limit of quantification, equipment linearity (working interval), method linearity as well as, method accuracy and precision. The average recoveries ranged between 76 and 106%, with the exception of chlorothalonil, which had an average recovery of 46%. Additionally, detection limits from 0.9 to 7.6ng g -: (1) and the quantification limits from 3.00 to 25.47ng g -: (1) were estimated. In terms of linearity and precision, the results obtained were in the ranges considered adequate (R(2) ≥ 0.98 and coefficient of variation (CV) ≤ 20%), with the exception of aldrin (R(2) = 0.946, CV = 35.79%), lindane (R(2) = 0.917, CV = 32.91%) and chlorothalonil (R(2) = 0.8184, CV = 81.35%). The proposed method was used to evaluate pesticides in real soil samples, detecting concentrations over 1000ng g -: (1) for some pesticides. The method was correctly validated and provided for the rapid determination of pesticides in soil.

Detection of organophosphorous pesticides in soil samples with multiwalled carbon nanotubes coating SPME fiber.

A headspace solid phase microextraction (HS-SPME) technique using stainless steel fiber coated with 20 μm multi-walled carbon nanotubes (MWCNTs) and gas chromatography with thermionic specific detector (GC-TSD) was developed to determine organophosphorous pesticides (OPPs) in soil. Parameters affecting the extraction efficiency such as extraction time and temperature, ionic strength, the volume of water added to the soil, sample solution volume to headspace volume ratio, desorption time, and desorption temperature were investigated and optimized. Compared to commercial polydimethylsiloxane (PDMS, 7 μm) fiber, the PDMS fiber was better to be corrected as phorate, whereas the MWCNTs fiber gave slightly better results for methyl parathion, chlorpyrifos and parathion. The optimized SPME method was applied to analyze OPPs in spiked soil samples. The limits of detection (LODs, S/N = 3) for the four pesticides were <0.216 ng g(-1), and their calibration curves were all linear (r (2) ≥ 0.9908) in the range from 1 to 200 ng g(-1). The precision (RSD, n = 6) for peak areas was 6.5 %-8.8 %. The recovery of the OPPs spiked real soil samples at 50 and 150 ng g(-1) ranged from 89.7 % to 102.9 % and 94.3 % to 118.1 %, respectively.

Determination of Trace Organophosphorus Pesticides in Water Samples by Solid Phase Disk Extraction and Gas Chromatography-Thermionic Specific Detector

A simple, rapid, sensitive, and high-throughput method based on solid-phase disk extraction (SPDE) and a gas chromatography–thermionic specific detector (GC-TSD) is described for the determination of organophosphorus pesticides (OPPs) in water samples. The proposed SPDE sample pretreatment method was initially optimized and the optimum experimental conditions found were 500 mL water sample (pH 2.5–7.0) extracted and enriched by a C18 (octadecyl) solid phase extraction disk at flow rate of 5 to 50 mL/min and eluted by 5 mL of acetone and 3 × 5 mL methylene chloride. The linearity of the method ranged from 0.020 to 1.00 µg/L for dimethoate, methyl parathion, and malathion, with correlation coefficients ranging between 0.9976 and 0.9992. The concentration factors for OPPs were between 498 and 554. The limits of detection were in the ng/L level, ranging between 2.5 and 4 ng/L. The relative recoveries of spiked 3 OPPs (dimethoate, methyl parathion, and malathion) with external calibration method at different concentration levels in pure, fresh water, and sea water samples were 102–112%, 94–109%, and 99–104%, respectively, and with relative standard deviations of 4.1–6.2%, 3.4–4.6%, and 3.5–5.2% (n = 3), respectively. It is concluded that this method can be successfully applied for the determination of OPPs in pure water, fresh water, and sea water samples.

Bioanalytical methods for quantitation of levamisole, a widespread cocaine adulterant

Abstract Levamisole is an anthelminthic that was first used as a de-worming agent in humans and animals. It has also been used to treat inflammatory conditions as well as certain types of cancer. Levamisole was discontinued for human use in the early 21st century due to toxic side effects including agranulocytosis and vasculitis. Recently, levamisole was discovered as a cocaine adulterant after reports emerged of drug users with the above disorders. As the prevalence of cocaine usage has grown in the last 15 years, measurement of levamisole in human samples has become increasingly important. This review focuses on the various bioanalytical methods available for the determination of levamisole in human plasma and urine. Earlier methods employed gas chromatography coupled with nitrogen-selective thermionic specific detection and nitrogen-phosphorus detection, as well as high performance liquid chromatography coupled with ultraviolet detection. In addition, gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) have also been described. Currently, GC-MS appears to be the method of choice however recent developments in the area of LC-MS/MS make this technology an attractive alternative. The merits of both GC-MS and LC-MS/MS for the determination of levamisole are evaluated on the basis of sample preparation, chromatographic separation conditions, run time, and analytical performance. In addition, emerging methods in this area are also reviewed.

Determination of Amitraz residue by headspace Gas Chromatography in honey and Beeswax samples from Iran

Amitraz, is an acaricide used to control the infestions produced by the mite Varroa jacobsoni in the beehives. Usage of this acaricide can cause the presence of it’s residue in honey and aparian products, same as beeswax. In the last few years, Amitraz was used more frequently in Iran. With regard to increasingly public concern about health risk from pesticide residues in the diet, the analysis of amitraz residues in honey and beeswax has received special attention. Amitraz is a very labile pesticide whose degradation products contain the 2,4-dimethylaniline moiety. The method has been validated for the analysis of amitraz and DMA (one of the most abundant amitraz degradation compound) in honey is static headspace solvent microextraction Gas chromatography with Thermionic Specific Detector (GC/TSD). In this study, 70 samples honey and beeswax from different beehives (Eastern and Western Azarbayjan, Ardabil territory, Iran) , markets and store s helves of (Tehran, Iran) were collected during (2006-2007) and analysis for detection of amitraz and DMA residues. It could be concluded that according to EU standard (MRL = 200µg/kg) all the samples of honey could be declared as appropriate for human consumption.

Headspace solvent microextraction-gas chromatographic thermionic specific detector determination of amitraz in honey after hydrolysis to 2,4-dimethylaniline

A novel headspace solvent microextraction (HSME) method for the extraction of trace amounts of 2,4-dimethylaniline (2,4-DMA), produced after hydrolysis of amitraz, is presented. The hydrolysis reaction and HSME were carried out in a single step, and then the preconcentrated 2,4-DMA was analyzed gas chromatographically using a thermionic specific detector (TSD). Different parameters affecting the HSME procedure including the type of solvent, headspace volume, stirring rate, Na 2SO 4 content, solution and microdrop temperature, drop volume and extraction time were studied and optimized. The optimized conditions were 25 min solution equilibrium time, 10 min solvent equilibrium time, 5 mL headspace volume, 600 rpm stirring rate, 15% Na 2SO 4, solution temperature 60 °C, microdrop temperature 4 °C and microdrop volume 3 μL. The limit of detection (LOD) and limit of quantification (LOQ) of the method were 10 and 30 ng amitraz g −1 honey, respectively, and the dynamic linear range was from 0.03 to 10 μg amitraz g −1 honey. Finally, the proposed method was applied to the quantification of amitraz in spiked honey samples. Because of performing hydrolysis and extraction processes in a single step, the method provided a rapid, simple and sensitive approach to analysis of amitraz.

Multiresidue analysis of three groups of pesticides in washing waters from olive processing by solid-phase extraction-gas chromatography with electron capture and thermionic specific detection

A multiresidue solid phase extraction-gas chromatography (SPE-GC) method is developed for the analysis of 28 organochlorine (OCPs), organophosphorus (OPPs) and organonitrogen (ONPs) pesticides at ng l − 1 levels in washing water from olive processing. Pesticides are separated from the water matrix, containing estimable amounts of olive oil, by eluting them from a C 18 SPE cartridge using dichloromethane. The target compounds are determined in the final extract by gas chromatography using thermionic specific (TSD) and electron capture (ECD) detection. Recoveries range from 79% to 129% in spiked washing water samples and detection limits are between 1 and 4 ng l − 1 . The method was successfully applied to determine OCPs, OPPs and ONPs in 25 samples of water collected directly in the inlet and outlet of the washing devices of three olive mills at different locations in Jaén (Spain). The most frequently encountered pesticide residues were terbuthylazine, simazine and diuron. In some of the water samples coming from the inlet of the washing devices, terbuthylazine and diuron measured concentrations were above the concentration limits scheduled by law.

Determination of organophosphorus pesticides in cucumber and potato by stir bar sorptive extraction

Organophosphorus pesticides (OPPs) in vegetables were determined by stir bar sorptive extraction (SBSE) and capillary gas chromatography with thermionic specific detection (TSD). Hydroxy-terminated polydimethylsioxane (PDMS) prepared by sol–gel method was used as extraction phase. The effects of extraction temperature, salting out, extraction time on extraction efficiency were studied. The detection limits of OPPs in water were ≤1.2 ng/l. This method was also applied to the analysis of OPPs in vegetable samples and matrix effect was studied. Linear ranges of OPPs in vegetable samples were 0.05–50 ng/g with detection limits ≤0.15 ng/g and the repeatability of the method was less than 20% relative standard deviation.

Determination of amitraz in canine plasma by solid-phase microextraction–gas chromatography with thermionic specific detection

A simple and rapid analytical method is presented for the determination of amitraz in canine plasma samples using solid-phase microextraction (SPME) and gas chromatography with thermionic specific detection (GC-TSD). The best conditions for the SPME procedure were: direct extraction on a polydimethlysiloxane (PDMS) fiber with 100-μm film thickness; 400 μl of sample plasma matrix modified with 4 ml sodium borate solution (0.01 mol l −1, pH 6.5); extraction temperature 70 °C, with stirring at 2500 rpm for 45 min. The method was linear between 20 and 400 ng ml −1 with regression coefficients corresponding to 0.998 and coefficient of the variation of the points of the calibration curve lower than 15%. The lowest limit of quantification (LOQ) for amitraz in plasma was 20 ng ml −1. This LOQ was determined as the lowest concentration on the calibration curve in which the coefficient of variation was lower than 15%. The proposed method was applied to determine amitraz concentrations in canine plasma to look for toxicity after treatment with amitraz in a dipping bath.

Determination of herbicides residues in soil by small scale extraction

Herbicides such as trifluralin, simazine, atrazine, metribuzin and metolachlor are used in Brazilian agriculture. The efficiency of a small scale method for determination of these herbicides and two degradation products (deisopropylatrazine and deethylatrazine) in soil samples was evaluated. The compounds were extracted from soil samples (5 g) with 20 ml of ethyl acetate in a mechanical shaker for 50 min. Following the extraction, the supernatant was dried through anhydrous sodium sulphate, concentrated and analysed by high resolution gas chromatography (HRGC) with thermionic specific detection (TSD). Mean recoveries obtained from soil samples fortified at three different levels ranged from 81 to 115% with relative standard deviation (RSD) values varying from 1.2 to 12.7%. The method detection limits ranged from 0.01 to 0.06 mg kg-1. The methodology was applied using soil samples from farms located near the town of Araraquara, in the State of São Paulo, Brazil.

A Simple and Rapid Extraction for Gas Chromatographic Determination of Thiabendazole and Imazalil Residues in Lemons

A rapid and efficient method is described for the determination of thiabendazole and imazalil residues in lemons (peel and pulp). The procedure is based on the extraction with an hexane:ethyl acetate mixture (1:1, v/v) and gas chromatographic analysis using thermionic specific detection (TSD). The possibility of matrix effect was also studied. Mean recoveries from 8 replicates of fortified samples ranged from 79% to 109%, with relative standard deviation values between 2.4% to 12.8%. The detection and quantification limits of the method were 0.2 mg kg-1 and 0.5 mg kg-1, respectively.

Multiresidue method for the simultaneous determination of four groups of pesticides in ground and drinking waters, using solid-phase microextraction–gas chromatography with electron-capture and thermionic specific detection

A common sample preparation procedure capable of efficiently concentrating various groups of pesticides, taking advantage of universal detectors like the mass spectrometer or combined techniques of group selective detectors like gas chromatography–electron capture detection (ECD)/thermionic specific detection (TSD), is desirable in environmental analysis. Six solid-phase microextraction fibres available for analysis of semi-volatiles (7, 30 and 100 μm poly(dimethylsiloxane) (PDMS), 85 μm polyacrylate, 60 μm PDMS–divinylbenzene (PDMS–DVB) and 65 μm Carbowax–DVB) were evaluated and the 60 μm PDMS–DVB was selected for the simultaneous extraction of 34 compounds, included in the organochlorine (OCPs), organophosphorous (OPPs), pyrethroid and triazine pesticide groups. All parameters affecting the extraction efficiency from water samples, namely fibre coating, sample agitation, pH and ionic strength, extraction temperature and time, were optimised. The analytical procedure involves solid-phase microextraction extraction, gas chromatographic separation and subsequent ECD and TSD via a post-column splitter adjusted to a split ratio of 1:10, respectively. Detection limits in the range of 1–10 ng l −1 for OCPs, 1–30 ng l −1 for OPPs, 20–30 ng l −1 for pyrethroids and 8–50 ng l −1 for triazines are easily attainable with the optimised procedure. The method validated for ground and drinking waters has low cost of implementation and operation although it requires careful maintenance.

Determination of pesticide residues in coconut water by liquid–liquid extraction and gas chromatography with electron-capture plus thermionic specific detection and solid-phase extraction and high-performance liquid chromatography with ultraviolet detection

Two simple methods were developed to determine 11 pesticides in coconut water, a natural isotonic drink rich in salts, sugars and vitamins consumed by the people and athletes. The first procedure involves solid-phase extraction using Sep-Pak Vac C 18 disposable cartridges with methanol for elution. Isocratic analysis was carried out by means of high-performance liquid chromatography with ultraviolet detection at 254 nm to analyse captan, chlorothalonil, carbendazim, lufenuron and diafenthiuron. The other procedure is based on liquid–liquid extraction with hexane–dichloromethane (1:1, v/v), followed by gas chromatographic analysis with effluent splitting to electron-capture detection for determination of endosulfan, captan, tetradifon and trichlorfon and thermionic specific detection for determination of malathion, parathion-methyl and monocrotophos. The methods were validated with fortified samples at different concentration levels (0.01–12.0 mg/kg). Average recoveries ranged from 75 to 104% with relative standard deviations between 1.4 and 11.5%. Each recovery analysis was repeated at least five times. Limits of detection ranged from 0.002 to 2.0 mg/kg. The analytical procedures were applied to 15 samples and no detectable amounts of the pesticides were found in any samples under the conditions described.

Determination of phosphine in biogas and sludge at ppt-levels with gas chromatography-thermionic specific detection

A gas chromatographic (GC) system to measure free phosphine in biogas and matrix bound phosphine in manure and sludge is presented. The system consists of a sample preconcentration trap filled with glass beads, connected with a capillary GC equipped with a thermionic specific detector. With a trap temperature as low as −155 °C, a sampling flow of 20 ml/min and a typical total sample volume of 100 ml, free phosphine concentrations in the low ng/m 3 range and matrix bound phosphine in the low ng/kg dry matter range, can be accurately and reproducibly determined.

Determination of lamotrigine simultaneously with carbamazepine, carbamazepine epoxide, phenytoin, phenobarbital, and primidone in human plasma by SPME-GC-TSD.

A simple and rapid analytical method is presented for the determination of lamotrigine simultaneously with primidone, carbamazepine, carbamazepine epoxide, phenobarbital, and phenytoin in human plasma using solid-phase microextraction (SPME) and gas chromatography with thermionic specific detection. The best conditions for the SPME procedure is established as following: direct extraction on a 65-microm Carbowax-divinylbenzene fiber; 1.0 mL of a sample plasma matrix modified with 15% NaCl and 3 mL of a potassium phosphate buffer (pH 7.0); extraction temperature at 30 degrees C; and stirring at a rate of 2500 rpm for 15 min. The method shows good linearity between 0.05 and 40.0 microg/mL with regression coefficients ranging between 0.9965 and 0.9995 and a coefficient of variation of the points of the calibration curve lower than 10%. The lowest limit of quantitation for the plasma-investigated drugs varies from 0.05 to 0.20 microg/mL, according to the drug. The proposed method is sensitive enough to work into subtherapeutic and therapeutic concentrations, being that it is applied in pharmacokinetic studies and patient routine therapeutic drug monitoring.

Determination of herbicides residues in soil by small scale extraction

Herbicides such as trifluralin, simazine, atrazine, metribuzin and metolachlor are used in Brazilian agriculture. The efficiency of a small scale method for determination of these herbicides and two degradation products (deisopropylatrazine and deethylatrazine) in soil samples was evaluated. The compounds were extracted from soil samples (5 g) with 20 ml of ethyl acetate in a mechanical shaker for 50 min. Following the extraction, the supernatant was dried through anhydrous sodium sulphate, concentrated and analysed by high resolution gas chromatography (HRGC) with thermionic specific detection (TSD). Mean recoveries obtained from soil samples fortified at three different levels ranged from 81 to 115% with relative standard deviation (RSD) values varying from 1.2 to 12.7%. The method detection limits ranged from 0.01 to 0.06 mg kg-1. The methodology was applied using soil samples from farms located near the town of Araraquara, in the State of São Paulo, Brazil.

COMPARISON BETWEEN SOLID–PHASE EXTRACTION METHODS FOR THE CHROMATOGRAPHIC DETERMINATION OF ORGANOPHOSPHORUS PESTICIDES IN WATER

A solid-phase microextraction (SPME) procedure has been developed to ex tract eight organophosphorus pesticides (OPs) in water and the method was compared with a conventional solid phase extraction (SPE) technique. The extracted OPs were analyzed by gas chromatography using thermionic specific detection. Both extraction methods presented linear calibration at least over the concentration range investigated (100 to 1000 ng.mL−1 for SPE and 1 to 100 ng.mL−1 for SPME). SPME method presented higher sensitivity than SPE. The quantitation limits were between 0.1 to 1.0 ng.mL−1 for SPME depending upon the analyte, and 100 ng.mL−1 for SPE. The precision, as measured by the standard deviations (RSD), were in the range 3.6 % to 5.8 % for SPME and 2.4 % to 9.2 % for SPE. Along with the feature of being a solvent – free sampling technique, SPME offers additional benefits due to its high sensitivity, simplicity, and small size sample required (typically: SPE – 500 mL, SPME – 5 mL).

Ultra-trace analysis of pesticides by solid-phase extraction of surface water with carbopack B cartridges, combined with large-volume injection in gas chromatography

A method has been developed for determination of twenty-four polar pesticides—nine organophosphorus pesticides, thirteen organonitrogen compounds, and two triazine degradation products—in surface water. It entails extraction of the target pesticides from 1-L water samples by solid-phase extraction (SPE), then gas chromatography (GC) with large-volume (40 μL) injection. Filtered surface water, from the St Lawrence River in Canada and the River Loire and its tributaries in France, was extracted on cartridges filled with 500 mg Carbopack B (120–400 mesh). Analysis was performed by gas chromatography with a thermionic specific detector (GC-TSD) and a mass spectrometric (MS) detector. Overall percentage recoveries were satisfactory (>70%) for all target pesticides, with precision below 10%. Detection limits were between 0.5 and 4 ng L−1.