Analysis of flufenacet in soil, wheat grain and straw by gas chromatography

An analytical procedure for detecting residues of a new herbicide, flufenacet, in soil, wheat grain and straw by gas chromatographic method using various solvents and extraction methods was standardized. The best results were obtained when samples fortified with flufenacet and were extracted with acetone-0.2 M HCl (95:5) using a horizontal shaker for soil and Soxhlet extractor for plant samples. The clean up was done by partitioning with dichloromethane. The GC equipped with an electron-capture detector and a column packing of HP-1 as stationary phase and nitrogen as a carrier gas at a flow-rate of 15 ml min(-1) was used. Temperatures of oven, injector and detector were adjusted at 190, 210 and 270 degrees C, respectively. The retention time of flufenacet was 2.07 min. The herbicide recoveries ranged between 81 to 100% from the three matrices.     

Stereoselective separation and determination of triadimefon and triadimenol in wheat, straw, and soil by liquid chromatography-tandem mass spectrometry

A sensitive and rapid analytical method was developed for simultaneous determination of triadimefon (TF) and triadimenol (TN) stereoisomers in wheat, straw, and soil by liquid chromatography coupled with triple quadrupole mass spectrometry (LC-MS/MS). The direct enantioseparation of TF and TN was performed on a Lux cellulose-1 column packed with cellulose-tris-(3,5-dimethylphenylcarbamate). The effects of mobile-phase composition on the separation were investigated and stereoisomeric elution orders were confirmed with a polarimeter detector. The pesticides were extracted from samples with acetonitrile and cleaned up by solid-phase extraction or activated carbon. Based on the developed stereoselective LC-MS/MS method, for TF and TN stereoisomers, good linearities were obtained over the concentration range of 0.003-4 mg/L; recoveries were 84.2-102.7% in wheat, 84.0-104.0% in straw, and 85.2-106.8% in soil at spiked concentrations of 0.007-2.0 mg/kg; intra-day and inter-day assay precisions were below 12.2%. Limits of detection (LODs) and limits of quantification (LOQs) in wheat, straw, and soil were 0.001-0.005 mg/kg and 0.007-0.02 mg/kg, respectively. Finally, the method was successfully applied to detect TF and TN stereoisomers in wheat, straw, and soil samples from residual trials in farm.     

Analysis of Enestroburin Residues in Wheat and Soil by Solid Phase Extraction and High-Performance Liquid Chromatography

A method was developed for the determination of enestroburin residues in wheat grain, wheat straw, and soil by solid-phase extraction (SPE) and HPLC-UV. The analytes were extracted with acetonitrile, cleaned up by PestiCarb/NH₂ cartridges and determined by HPLC with UV detector. This method is characterized by recovery >88.0%, precision (RSD) <7.8% and sensitivity of 0.005 mg/kg, in agreement with directives for method validation in residue analysis. The proposed method was successfully employed for the determination of enestroburin residue levels and its dissipation rates in a field trial in Beijing, China. Dissipation study shows that the half life of enestroburin in wheat straw was 5.35–5.81 days and in soil was 6.13–6.75 days. When enestroburin was applied according to the recommended dose and doubled dose, the final residue in wheat grain was both lower than 0.2 mg/kg. A harvest interval should be more than 7 d, and a dosage of 100–200 g (a.i.)/ha was suggested and considered as safe to human beings and animals.     

Simultaneous determination of pseudoephedrine hydrochloride and diphenhydramine hydrochloride in cough syrup by gas chromatography (GC)

A simple, rapid and precise gas chromatographic method has been developed for the simultaneous determination of pseudoephedrine hydrochloride and diphenhydramine hydrochloride in cough syrup, using a SS column of 10% OV 1 on chromosorb W-HP (80-100 mesh) and nitrogen as a carrier gas at a flow rate of 30 ml min(-1). The oven temperature was programmed at 135 degrees C for 1 min, with a rise of 10 degrees C min(-1) up to 250 degrees C (held for 5 min). The injector and detector port temperatures were maintained at 280 degrees C. Detection was carried out using Flame ionization detector. Guaphenesin was used as an internal standard. Results of assay and recovery studies were statistically evaluated for its accuracy and precision.     

Plasma-Assisted Pretreatment of Wheat Straw

O₃ generated in a plasma at atmospheric pressure and room temperature, fed with dried air (or oxygen-enriched dried air), has been used for the degradation of lignin in wheat straw to optimize the enzymatic hydrolysis and to get more fermentable sugars. A fixed bed reactor was used combined with a CO₂ detector and an online technique for O₃ measurement in the fed and exhaust gas allowing continuous measurement of the consumption of O₃. This rendered it possible for us to determine the progress of the pretreatment in real time (online analysis). The process time can be adjusted to produce wheat straw with desired lignin content because of the online analysis. The O₃ consumption of wheat straw and its polymeric components, i.e., cellulose, hemicellulose, and lignin, as well as a mixture of these, dry as well as with 50% water, were studied. Furthermore, the process parameters dry matter content and milled particle size (the extent to which the wheat straw was milled) were investigated and optimized. The developed methodology offered the advantage of a simple and relatively fast (0.5–2 h) pretreatment allowing a dry matter concentration of 45–60%. FTIR measurements did not suggest any structural effects on cellulose and hemicellulose by the O₃ treatment. The cost and the energy consumption for lignin degradation of 100 g of wheat straw were calculated.     

A liquid chromatography with tandem mass spectrometry method to simultaneously determinate chlorpyrifos,imidacloprid and imidacloprid metabolites in wheat

A liquid chromatography with tandem mass spectrometry method was developed and validated to simultaneously determine chlorpyrifos, imidacloprid, and imidacloprid metabolites in soil, wheat grain, and wheat straw matrices. Satisfactory linearity (R² ≥ 0.9965) of the method was obtained for all analytes. The ranges of limits of detection and limits of quantification for seven analytes in three matrices were 0.17–66.7 and 0.5–200 μg/kg, respectively. Average recoveries were 72.85–81.25% for chlorpyrifos, 78.54–84.70% for imidacloprid, 73.83–81.03% for imidacloprid olefin, 71.47–80.61% for 5‐hydroxy imidacloprid, 71.79–81.32% for imidacloprid urea, 70.42–82.20% for imidacloprid nitroguanidine, and 70.91–82.46% for imidacloprid 6‐chloronicotinic acid in soil, wheat grain, and wheat straw. The intra‐ and interday relative standard deviations were less than 8%. The established method was successfully applied for the residual analysis of chlorpyrifos, imidacloprid, and imidacloprid metabolites in actual soil, wheat grain, and wheat straw samples. The results indicated that the established method could be used to detect trace amounts of chlorpyrifos, imidacloprid, and imidacloprid metabolites in wheat and that the method might be able to provide some data on the detection of these seven compounds in other crops.     

Capillary column gas chromatographic method using electron-capture detection for the simultaneous determination of nicardipine and its pyridine metabolite II in plasma

A rapid, specific and direct method based on capillary column gas chromatography with electron-capture detection is described for the simultaneous determination of nicardipine, a new calcium antagonist, and its pyridine metabolite II in human plasma. In this method, the nicardipine, its pyridine metabolite II and internal standard are extracted from the plasma and then partially purified by acid-base partitioning prior to the final injection onto the capillary column gas chromatograph for quantification by means of an electron-capture detector. The quantification limit of the method is 1 ng/ml of plasma for both nicardipine and its pyridine metabolite II. The coefficients of variation for nicardipine and the pyridine metabolite II at concentrations of 1-50 ng/ml are less than 7% and less than 9% (n = 4), respectively. The method has been validated against a previously developed high-performance liquid chromatographic method (sensitivity 5 ng/ml).     

A novel method for the calibration of Kováts retention indices using n-alkanes with a thermionic nitrogen-phosphorus specific detector

This paper describes a novel method for the detection of compounds that do not contain nitrogen or phosphorus by a thermionic nitrogen-phosphorus specific detector (NPD), which normally detects only nitrogen- or phosphorus-containing compounds. This method allows for the calibration of gas chromatographic columns with NPD detectors using n-alkanes instead of nitrogen-containing drug mixtures. This results in a more rapid and accurate calibration for the calculation of relative retention indices (RRI), such as Kováts indices, than was previously possible when employing an NPD detector. The proposed method describes the temporary conversion of the NPD detector into a detector with properties much like a flame ionization detector. After a deliberate increase in the hydrogen gas flow rate to the thermionic bead from 4 ml/min to 8 ml/min, the n-alkanes (containing no nitrogen) can be detected and used as RRI calibrators. Once the column has been calibrated, the hydrogen gas flow rate is lowered to the normal rate of 4 ml/min. The detector then behaves as a normal NPD, no longer detecting the n-alkanes.     

Development of a multi-residue screening method for the determination of pesticides in cereals and dry animal feed using gas chromatography-triple quadrupole tandem mass spectrometry

A multi-residue screening method for simultaneous analysis of 122 gas chromatography amenable pesticides in dry matrices such as cereal grain and certain feedingstuffs was developed. The method entails a simple extraction of re-hydrated sample with acetonitrile followed by a dispersive solid phase extraction (dispersive-SPE) clean-up step prior to the final determination by gas chromatography/triple quadrupole tandem mass spectrometry (GC-MS/MS). Due to complexity of analyzed matrices, two MS/MS transitions were set for each pesticide to eliminate the need for re-analysis of potentially positive samples, and provide unequivocal identification of detected pesticides in accordance with recent guidelines, in a single analytical run. Thus, in the developed GC-MS/MS acquisition method, a total of 216 different multiple reactions monitoring (MRM) transitions were monitored in one set of experimental conditions. To evaluate performance of the method, validation experiments were carried out on wheat grain at three spiking levels (0.01, 0.02 and 0.05 mg kg(-1)). Additional recovery tests at 0.05 mg kg(-1) were carried out on several other matrices. The recoveries ranged between 73 and 129% with associated relative standard deviations between 1 and 29% for the majority of pesticides. Limits of detection were less or equal to 0.01 mg kg(-1) for approximately 68% of pesticides. The applicability of the proposed method to detect and quantify pesticide residues has been demonstrated in the analysis of 136 real samples. Additionally, the method was favorably compared with an acetone extraction method (accepted as a reference method by some of European and U.S. authorities) in the analysis of real samples known to contain pesticide residues.     

Determination of busulfan in human plasma by gas chromatography with electron-capture detection

A simple and highly sensitive gas chromatographic method has been developed for the determination of busulfan in human plasma. After extraction of plasma specimens (clinical or spiked) with ethyl acetate, busulfan and the internal standard [1,8-bis(methanesulfonyloxy)octane] were derivatized with 2,3,5,6-tetrafluorothiophenol to yield compounds monitored by a 63Ni electron-capture detector. Sample recoveries from extraction and derivatization were greater than 78 and 91%, respectively. The limit of quantitation was 0.01 microgram/ml (0.04 microM) in 1 ml of plasma with a linear relationship over the 0.01-1.0 micrograms/ml (0.04-4 microM) concentration range. The method has been applied to analyze the plasma versus time profile of busulfan in human subjects following administration of an oral dose of 4 mg/kg per day as a marrow ablative chemotherapy for bone marrow transplantation.     

Automated capillary gas chromatographic assay using nitrogen-phosphorus ionization detection for the determination of bepridil in human plasma

A highly sensitive and specific capillary gas chromatographic method for the determination of the antianginal drug bepridil in plasma is described. The capillary gas chromatograph and nitrogen-selective detector combination provides excellent sensitivity for clinical samples. The lowest concentration of bepridil which can be measured accurately and precisely in a 1-ml plasma sample is 1 ng/ml. Standard curves are linear over the concentration range 1-60 ng/ml. Accuracy and precision of the assay, expressed as relative deviation from the true value and relative standard deviation (inter-run) are less than 15% at all concentrations in the linear range. No interfering peaks are observed. Using an automatic injector and a laboratory computer system, sixty samples can be analyzed routinely in one day. The present assay has been successfully cross-validated with a published high-performance liquid chromatographic assay.     

Determination of 1,2-benzisoxazole-3-acetamidoxime hydrochloride (PE-257) in plasma using electron-capture gas chromatography

A gas chromatographic method has been developed that permits the accurate and specific determination of a new psychotropic agent, PF-257, in plasma. PF-257 is extracted with ethyl acetate from alkaline plasma and, after a clean-up procedure, derivatized with heptafluorobutyric anhydride to form 3-[(5-n-heptafluoropropyl-1,2, 4-oxadiazol-3-yl)methyl]-1,2-benzisoxazole (HOMB). The HOMB is assayed on a gas chromatograph equipped with an electron-capture detector. Accurate determinations of PF-257 are possible in the concentration range from 1-40 ng/ml with a relative standard deviation of 6.8%. The minimum detectable concentration in plasma is 0.1 ng/ml. Plasma levels of PF-257 in rats receiving intravenous or oral dosing (10 mg/kg) were determined.     

Determination of 3-(5-tetrazolyl) thioxanthone 10,10-dioxide in human plasma, urine and faeces.

A gas chromatographic method is described for assay of 3-(5-tetrazolyl) thioxanthone 10,10-dioxide (BW 59C) in human plasma, urine and faeces. After extraction into 1,2-dichloroethane from alkaline medium the compound is converted to the heptafluorobutyrate derivative which is injected into a gas chromatograph and measured using a 63Ni electron capture detector. The assay produces a linear calibration curve over the range 0-30 mug/ml when the internal standard method is used. Reproducibility is good and sensitivity down to 1 ng injected on column is possible. The method has been used to investigate the pharmacokinetic properties of BW 59C in man and has been semi-automated by the use of an autosampler and dedicated computer.     

Determination of deoxynivalenol (vomitoxin) by high-performance liquid chromatography with electrochemical detection

A rapid method for the analysis of deoxynivalenol (DON) was developed using high-performance liquid chromatography (HPLC) with reductive electrochemical detection (ED). Deoxynivalenol produced by Fusarium roseum growing on solid cornmeal and rice substrates and from naturally contaminated wheat was extracted and quantitated via ED. DON levels in wheat were verified by gas chromatography and structurally confirmed by mass spectrometry. DON was optimally resolved by HPLC employing a radially compressed octadecylsilane column and a mobile phase of deoxygenated methanol-40 mM borate buffer (35:65) at a flow-rate of 1.0 ml/min. Under these conditions DON exhibited an average retention time of 3.6 min. Reductive ED (-1.4 V) allowed a 12-fold increase in sensitivity and greater selectivity than classical UV absorption at 224 nm. A detection limit for DON of 25 pg/microliter was achieved under these conditions. The determination of DON in crude grain extracts was hindered by extractable interfering substances, whereas ED was more functional-group selective (i.e. reduction of the carbonyl moiety). ED permits a direct quantitation of DON from crude grain extracts and may facilitate the determination of this agent and associated metabolites in biological samples.     

Identification and quantification of lignans in wheat bran by gas chromatography-electron capture detection

Whole grain cereals are an important source of bioavailable lignans, the group of compounds with potential anti-cancerogenic, antioxidant, anti-proliferative, pro-apoptotic, and antiangiogenic properties. The aim of this work was to develop a sensitive method for determination of wheat bran lignans. The analysis of lignans secoisolariciresinol, hydroxymatairesinol, lariciresinol, matairesinol, pinoresinol, syringaresinol is based on derivatization with pentafluoropropionic anhydride (PFPA) and gas chromatography-electron capture detection (GC-ECD), using styrene glycol as internal standard. To our knowledge, this is the first time that EC detection has been used for lignan analysis. The results show that the technique is reproducible and sensitive enough for detecting lignans in wheat at parts-per-billion (ppb) levels, except for hydroxymatairesinol. The method developed showed good recovery (85-105%) and precision (4-20%) for five types of lignans and thus represents a simpler and more affordable alternative to state-of-the-art wheat lignan liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis.     

Microwave-assisted derivatization and single-drop microextraction for gas chromatographic determination of chromium(III) in water

A rapid and efficient sample preparation method combining microwave-assisted derivatization (MAD) and single-drop microextraction (SDME) for the gas chromatographic (GC) determination of trace Cr(III) in water was developed. Aqueous Cr(III) was first converted to the volatile chromium trifluoroacetylacetonate (Cr(tfa)3) by reaction with 1,1,1-trifluoroacetylacetone (Htfa) under the irradiation of microwave. Derivatization of Cr(III) at ng ml(-1) level could be completed in less than 1 min. The formed Cr(tfa)3 was then extracted into a small droplet (2 microl) of toluene suspended at the tip of a microsyringe needle. The optimal extraction time was 30 min. The solvent drop was directly injected into a GC equipped with a flame photometric detector (FPD) for analysis. The two Cr(tfa)3 isomers extracted could be efficiently separated in 2 min. Linearity (r>0.99) over the concentration range 2-300 ng ml(-1) Cr was obtained and the limit of detection was 0.5 ng ml(-1) Cr. The relative standard deviation was 7.8% at 20 ng ml(-1) Cr (n=5). Applicability of this method to water analysis was examined by analyzing the chromium content in a reference standard water sample and an industrial effluent.     

Determination of alpha- and beta-zearalenol and zearalenone in cereals by gas chromatography with ion-trap detection.

A method for determination of estrogenic mycotoxins, alpha- and beta-zearalenol and zearalenone, in cereals (wheat, barley, oats, corn) is described. After extraction with ethylacetate, clean-up involved a base treatment and partition with water; derivatization was by trimethylsilylation. For quantitation and confirmation a capillary gas chromatograph combined with a selective mass detector (ion trap), working in the electron impact-mode was used. The detection limit for the complete method is 1 microgram/kg for each of the three mycotoxins in full scan. Recoveries from spiked cereals were 82-86%.     

Gas-liquid chromatographic determination of moprolol (SD 1601) in human plasma and urine

1-(o-methoxyphenoxy)-3-isopropylamino-2-propanol hydrochloride (moprolol, Omeral^R), is a new β-adrenergic blocking agent. A gas chromatographic method for determining unchanged moprolol in human biological fluids has been developed. After solvent extraction, a bis-trifluoroacetyl derivative was formed and measured by an electron capture detector. The quantification was checked by using an internal standard (pronethalol), which was added to all samples. The electron capture response was linear between 10 and 500 ng/ml. To avoid contamination of the peaks, careful extraction was imperative. The main advantages offered by the described method are: specificity, high sensitivity (10 ng.ml^?1) and the small amount of biological fluids (1 ml plasma a. e.) required.     

Determination of lidocaine in human serum by capillary gas chromatography with surface ionization detection

A novel analytical method has been developed for the determination of lidocaine (2-(diethylamino)-N-(2,6-dimethyl)phenylacetamide) in human serum. After solvent extraction from serum the extract was analyzed by gas chromatography employing a van den Berg type solventless injector, a new sensitive and selective detector, the surface ionization detector, and a bonded phase flexible fused silica capillary column. The detection limit was ca. 30–50 ng/ml.     

The Effect of Temperature on the Structure and Function of a Cellulose-Degrading Microbial Community

The purpose of this study was to investigate the effect of temperature on the structure and straw degradation capability of a microbial community grown from wheat straw compost. Two cellulolytic microbial communities, WDC1 and WDC2, were obtained from compost. The communities had been cultured under 50 and 60?°C by continuous enrichment, respectively. The wheat straw degradation capabilities were 45.69?% (WDC1) and 59.5?% (WDC2). By changing the culture temperatures, two new stable communities were obtained: WDC1-6N (WDC1, cultivated at 60?°C for eight generations) and WDC2-5N (WDC2, cultivated at 50?°C for eight generations). The wheat straw degradation capabilities for the new communities were 59.75 and 52.60?%, respectively. The results showed that compared to 50?°C, the wheat straw degradation capability of the communities cultured at 60?°C was stronger. Sequencing of selected denaturing gradient gel electrophoresis (DGGE) bands and analysis of DGGE profiles indicated that the WDC2 structure was significantly different from the structure of WDC1. This was so even though the two communities were enriched from the same compost. With the change of culture temperature, the community structures underwent significant transitions. Included communities were thermophilic, anaerobic bacteria, and any cellulolytic bacteria (e.g., Clostridium thermocellum) that were active and abundant at conditions under 60?°C. These results have the potential to significantly aid in the enrichment of a cellulose-degrading community from the environment and to enhance the community capability to conduct straw biotransformation.