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1.
Enzyme-linked immunosorbent assay (ELISA) data from surface water reconnaissance were compared to data from samples analyzed by gas chromatography for the pesticide residues cyanazine (2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile) and metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide). When ELISA analyses were duplicated, cyanazine and metolachlor detection was found to have highly reproducible results; adjusted R2s were 0.97 and 0.94, respectively. When ELISA results for cyanazine were regressed against gas chromatography results, the models effectively predicted cyanazine concentrations from ELISA analyses (adjusted R2s ranging from 0.76 to 0.81). The intercepts and slopes for these models were not different from 0 and 1, respectively. This indicates that cyanazine analysis by ELISA is expected to give the same results as analysis by gas chromatography. However, regressing ELISA analyses for metolachlor against gas chromatography data provided more variable results (adjusted R2s ranged from 0.67 to 0.94). Regression models for metolachlor analyses had two of three intercepts that were not different from 0. Slopes for all metolachlor regression models were significantly different from 1. This indicates that as metolachlor concentrations increase, ELISA will over- or under-estimate metolachlor concentration, depending on the method of comparison. ELISA can be effectively used to detect cyanazine and metolachlor in surface water samples. However, when detections of metolachlor have significant consequences or implications it may be necessary to use other analytical methods.  相似文献   

2.
The major flavanone-7-O-glycoside constituents in citrus fruit juices (naringin, hesperidin, neohesperidin, narirutin, and eriocitrin) were separated as diastereomers by multidimensional liquid chromatography. The method consisted of coupling two HPLC columns: a reversed-phase (RP(18)) column was used for the separation of flavanone glycosides, which were, then, individually switched into a carboxymethylated beta-cyclodextrin (beta-CD)-based column and resolved as the corresponding stereoisomers. The method was used for the full analysis of flavanone glycosides in fresh hand-squeezed and commercial fruit juices by combining the quantitative estimation with the diastereomeric analysis. Quantitative data were in general consistent with previously reported data in this field. CC-LC isomer analysis was carried out by coupling the beta-CD column with a mass spectrometer operated with negative ion electrospray ionization (ESI-MS). The results showed that hesperidin was present in orange juices almost exclusively as the 2S isomer, whereas narirutin had mainly the 2R configuration. In grapefruit juices (2S)-naringin prevailed with the respect to the 2R isomer, whereas the opposite was true for narirutin. Lemon juices contained eriocitrin stereoisomers in equal amount (50% each), but hesperidin was almost exclusively found as the 2S isomer. Significant differences of the diastereomeric ratios were observed between freshly squeezed juices and juices from commercial sources.  相似文献   

3.
Chiral stability of synthetic pyrethroid insecticides   总被引:6,自引:0,他引:6  
Synthetic pyrethroids are chiral compounds consisting of multiple stereoisomers. Evaluation of enantioselectivity in environmental fate and ecotoxicity requires analytical methods that preserve stereoisomer integrity during analysis. In this study, we characterized the stability of stereoisomers from four commonly used pyrethroids, cis-bifenthrin (cis-BF), permethrin (PM), cypermethrin (CP), and cyfluthrin (CF), during gas chromatography (GC) analysis and sample preparation. Stereoisomers of cis-BF and PM were found to be stable, but those of CP and CF were unstable, under heat or in water. Isomer conversion occurred only at the alphaC in CP or CF, causing the analyte stereoisomer to convert to an epimer. At a GC inlet temperature of 260 degrees C, about 9% conversion occurred for CP and CF. In organic solvents and sterile water, stereoisomers of cis-BF and PM were stable, but slow isomer conversion was observed for CP and CF in water at ambient temperature. However, isomer conversion for CP and CF was relatively insignificant (2-3%) when the GC inlet temperature was kept at < or = 180 degrees C or when on-column injection was used. Isomer conversion at the alphaC in water suggests that abiotic processes may also contribute to enantioselectivity observed in the environment for pyrethroids with the asymmetric alphaC.  相似文献   

4.
Isomer selectivity in aquatic toxicity and biodegradation of cypermethrin   总被引:10,自引:0,他引:10  
Synthetic pyrethroids (SPs) are widely used in both agricultural and urban regions for insect control. Unlike many other pesticides, SPs are chiral compounds consisting of stereoisomers. However, occurrence of isomer selectivity in environmental processes is poorly understood for SPs. We evaluated isomer selectivity in toxicity of cypermethrin (CP) to Ceriodaphnia dubia and in its biodegradation by microbial isolates and in sediment. Among the eight enantiomers, two enantiomers (1R-cis-alphaS and 1R-trans-alphaS) were found to be toxic to C. dubia. Bacteria strains isolated from sediment selectively degraded CP diastereomers and enantiomers. The trans diastereomers were preferentially degraded over the cis diastereomers. Of the two active enantiomers, 1R-cis-alphaS was degraded slower, whereas 1R-trans-alphaS was degraded faster than the other stereoisomers. Similar isomer selectivity was observed during CP degradation in whole sediment. Since ecotoxicity is likely caused only by the biologically active enantiomers, knowledge on isomer selectivity may improve our understanding of the ecological risks of CP and analogous SPs.  相似文献   

5.
Separation of chiral enantiomers and the dissipation of rac-metolachlor and S-metolachlor in soil were evaluated using achiral high-performance liquid chromatography (HPLC) and chiral gas chromatography (GC) methods. Under the experimental conditions the possible metabolite was considered to be N-(2-ethyl-6-methyl-phenyl)-2-hydroxy-acetamide. Because of the presence of two chiral elements (asymmetrically substituted carbon and chiral axis), the baseline separation of metolachlor enantiomers was not achieved. S-metolachlor degraded faster in soil than rac-metolachlor. After a 42-day incubation, 73.4% of rac-metolachlor and 90.0% of S-metolachlor were degraded. However, due to the absence of biological processes the degradation process in sterilized soil showed no enantioselectivity. The results indicated that enantioselective degradations could greatly affect the environmental fate of metolachlor and should be considered when the environmental behavior of these compounds was assessed.  相似文献   

6.
A series of four isomeric 3,9-dihydroxymegastigma-4,6,7-trienes, 8, has been prepared. The (3S,6R,9S) isomer of 8 proved to be identical to an isomer of this compound tentatively identified as an intermediate in the formation of damascenone from an allene triol. Each of the four isomers, when hydrolyzed independently of each other at pH 3.0 and 25 degrees C, produced product mixtures in which the major product was damascenone (1). Contrary to expectation, 3-hydroxydamascone (5) was not observed in any of the hydrolyses. Consequently, the mechanism of formation of damascenone proposed earlier requires modification. In each hydrolysis, the product mixtures showed the presence of a second isomer of 8, produced by epimerization during hydrolysis. Chiral analysis on a Cyclosil B column revealed that this epimerization was occurring at C(3) in each of the hydrolyses.  相似文献   

7.
A multiresidue method was developed for the simultaneous determination of low parts per billion (ppb) concentrations of the herbicides alachlor, metolachlor, atrazine, and simazine in water and soil using isotope dilution gas chromatography/mass spectrometry (GC/MS). Known amounts of 15N,13C-alachlor and 2H5-atrazine were added to each sample as internal standards. The samples were then prepared by a solid phase extraction with no further cleanup. A high resolution GC/low resolution MS system with data acquisition in selected ion monitoring mode was used to quantitate herbicides in the extract. The limit of detection was 0.05 ppb for water and 0.5 ppb for soil. Accuracy greater than 80% and precision better than 4% was demonstrated with spiked samples.  相似文献   

8.
Germination stimulants for root holoparasitic weeds broomrapes ( Orobanche and Phelipanche spp.) produced by tobacco ( Nicotiana tabacum L.) were purified and characterized. The root exudates of tobacco contained at least five different stimulants, and LC-MS/MS analyses revealed that four of them were strigolactones; a tetradehydrostrigol isomer, a didehydrostrigol isomer, and two strigol isomers. The two isomers of strigol were identified as (+)-orobanchol and its 2'-epimer by comparison of NMR and GC- and LC-MS data with those of synthetic standards. The structure of the tetradehydrostrigol isomer, the major stimulant of the bright yellow tobacco cultivars, was determined as 4-alpha-hydroxy-5,8-dimethyl-GR24 [( E)-4-alpha-hydroxy-5,8-dimethyl-3-(4-methyl-5-oxo-2,5-dihydrofuran-2-yloxy)methylene)-3a,4-dihydro-3 H-indeno[1,2- b]furan-2(8b H)-one] and named solanacol. 2'-Epi-orobanchol and solanacol are the first natural strigolactones having a 2'-epi stereochemistry and a benzene ring, respectively.  相似文献   

9.
A liquid chromatographic (LC)-fluorometric method is described for the determination of cis- and trans-isoeugenol (2-methoxy-4-propenylphenol) in perfumes, colognes, and toilet waters. A test portion of the product is added to diethyl ether, and the isoeugenol isomers are extracted with sodium hydroxide solution. The basic extract is then acidified, and the isoeugenol isomers are extracted with isooctane. Aliquots of the isooctane extract are analyzed by using a silver ion cation exchange LC column interfaced to a spectrophotofluorometer. Each isomer in the product is determined by comparing its fluorescence emission intensity with that of an external standard consisting of a mixture of both isomers in which the relative concentration of each has been determined. Average recoveries from various commercial fragrances fortified with a mixture of cis- and trans-isoeugenol with total isoeugenol content of 0.1, 0.5, and 4.0 mg/mL ranged from 87 to 105% for the trans-isomer (SD = 4.6%) and from 83 to 113% for the cis-isomer (SD = 6.7%). The limit of determination is approximately 0.002 mg/mL.  相似文献   

10.
Malonylglucoside isomers were identified by high-performance liquid chromatography with ultraviolet/mass spectrometric detection and nuclear magnetic resonance (NMR). The formation and interconversions of the isomers were monitored in heated buffer and soymilk systems. Two positional or steroisomers of malonylgenistin and malonydaidzin, showing similar UV spectra and molecular weights yet different fragmentation patterns, were detected. NMR characterization of the malonylgenistin isomer revealed its structure to be 4'-O-malonylgenistin, suggesting a malonyl migration from the glucose-6 position to the glucose-4 position. Interconversions of malonylgenistin and its isomer were observed in both buffered and soymilk systems. While malonylgenistin partially converted to the isomer upon thermal treatment, conversion of the isomer to malonylgenistin was more spontaneous. The malonylgenistin isomer represented 6-9% of the total calculated genistein content in soymilk heated at 100 °C for various periods of time. Consequently, disregarding the content of malonylglucoside isomers in processed soy matrices can lead to isoflavone underestimation and misinterpretation of the biological contributions.  相似文献   

11.
All synthetic pyrethroids are chiral compounds, and isomerization has been frequently observed from exposure to certain solvents. However, so far, pyrethroid isomerization caused by solvents has not been characterized at the enantiomer level. In this study, we evaluated the occurrence of enantiomerization of two commonly used pyrethroids, permethrin and cypermethrin, in various organic solvents and solvent-water systems. The four stereoisomers of permethrin were stable under all test conditions. Rapid enantiomerization of cypermethrin was observed in isopropanol and methanol but not in n-hexane, acetone, or methylene chloride. After 4 days at room temperature, 18-39% conversions occurred for the different cypermethrin stereoisomers in isopropanol and methanol, and the enantiomerization invariably took place at the alpha-carbon position. The extent of enantiomerization was affected by temperature dependence and was also influenced by water as a cosolvent. In solvent-water mixtures, cypermethrin underwent gradual enantiomerization in acetone-water and rapid enantiomerization in isopropanol-water or methanol-water. The extent of enantiomerization varied among the solvents and as a function of the solvent-to-water ratio. Results from this study suggest that exposure to certain solvents and water may cause artifacts in chiral analysis and that for isomer-enriched pyrethroid products, such abiotic enantiomerization may render the products less effective because the conversion leads to the formation of inactive stereoisomers.  相似文献   

12.
The pungent compounds piperine and isomers thereof, secondary metabolites present in black and white pepper fruit, undergo light-induced isomerizations. To facilitate studies in this area, an HPLC method has been developed for analysis and isolation of the following four possible piperine-derived photoinduced isomers: piperine, isopiperine, chavicine, and isochavicine. The limits of detection (LOD) estimated from calibration plots were approximately 15-30 ng for each isomer. Reproducibilities of the analyses were excellent, and recoveries of spiked samples were as follows (average +/- SD; n = 3): chavicine, 98.4 +/- 2.1%; isopiperine, 96.2 +/- 3.2%; piperine, 104 +/- 3.8%; isochavicine, 98.9 +/- 3.0%. To determine the kinetics of these isomerizations, fluorescent light, sunlight, and UV radiation at 254 nm was used to induce cis-trans geometric isomerization as a function of light intensities and time of exposure determined with the aid of high-performance liquid chromatography (HPLC) and liquid chromatography with diode array UV detection-mass spectrometry (LC-DAD/MS). HPLC was also used to determine the distribution of the isomers in four commercial ground black pepper products used as spices in culinary practice. Isomerization increased with light intensities and time of exposure and leveled off at the so-called photostationary phases. The piperine levels of the four products were quite similar, ranging (in wt %) from 10.17 to 11.68. The amounts of the other three isomers ranged from 0.01 to 0.07 of the total for chavicine; from 0.15 to 0.23 for isopiperine; and from 0.37 to 0.42 for isochavicine. The results establish the utility of the HPLC method for simultaneous analysis of the four isomers both in pure form and in black pepper extracts. The dietary significance of the results is discussed.  相似文献   

13.
An improved analytical method for the determination of geosmin in red beets was developed using headspace solid-phase microextraction (HSPME). Volatiles of beet juice were extracted in headspace for 2 h using a polydimethylsiloxane/divinylbenzene fiber, thermally desorbed from the fiber, and analyzed by gas chromatography. The HSPME method was determined to be suitable for geosmin analysis as evidenced by high relative recovery (99.2%), low relative standard deviation (7.48%), and reasonable detection limit (1 microg/kg of beet root tissue). The concentrations of geosmin in four beet cultivars ranged from 9.69 +/- 0.22 to 26.7 +/- 0.27 microg/kg, depending on cultivar.  相似文献   

14.
In normal onion (Allium cepa), trans-S-1-propenyl-L-cysteine sulfoxide is transformed via 1-propenesulfenic acid into propanethial S-oxide, a lachrymatory factor, through successive reactions catalyzed by alliinase and lachrymatory factor synthase (LFS). A recent report showed that suppression of the LFS activity caused a dramatic increase in thiosulfinates previously reported as "zwiebelane isomers". After purification by recycle high-performance liquid chromatography and subsequent analyses, we established the planar structure of the putative "zwiebelane isomers" as S-3,4-dimethyl-5-hydroxythiolane-2-yl 1-propenethiosulfinate, in which two of the three molecules of 1-propenesulfenic acid involved in the formation gave the thiolane backbone, and the third molecule gave the thiosulfinate structure. Of at least three stereoisomers observed, one in the (2'R,3'R,4'R,5'R)-configuration was collected as an isolated fraction, and the other isomers were collected as a combined fraction because spontaneous tautomerization prevented further purification. Both fractions showed inhibitory activities against cyclooxygenase-1 and α-glucosidase in vitro.  相似文献   

15.
Purified solutions of all-trans retinyl palmitate, retinol, and retinaldehyde in chloroform, methylene chloride, or hexane were exposed to white light or gold fluorescent light or were kept in the dark, and the resulting isomer distributions were determined by LC (liquid chromatography). No significant isomerization of any of the retinoids occurred either in the dark or on exposure to gold light in any of the solvents tested. However, a large amount of the 9-cis isomer and only much smaller amounts of other cis isomers were produced when retinol or retinyl palmitate in chloroform or methylene chloride solution was exposed to white light. The isomerization pattern of retinyl palmitate in chloroform was not altered by the addition of free-radical scavengers, addition of an organic base, or substitution of deuterochloroform for chloroform as solvent. Use of other polar solvents such as tetrahydrofuran, acetone, or methanol produced isomer distributions similar to those obtained in chloroform solution. Retinol and retinyl palmitate in hexane solution, on exposure to white light, were isomerized much less extensively than in chloroform or methylene chloride and produced a significant amount of the 13-cis, as well as the 9-cis, isomer. Isomerization of retinaldehyde in chloroform or in methylene chloride solution under white light yielded 13-cis, 11-cis, 9-cis, and 7-cis isomers, in order of decreasing amount, whereas in hexane solution, only the 13-cis and 9-cis isomers were produced in significant quantity.  相似文献   

16.
Herbicides atrazine and metolachlor have been detected in water bodies across the world. The objective of this study was to assess the efficiency of 0‐m, 3‐m, 6‐m and 9‐m grass filter strips to reduce masses of dissolved metolachlor, atrazine and deethylatrazine (a degradation product of atrazine) exported in runoff. For that purpose, 16 uncultivated plots (3‐m wide × 65‐m long) with 0‐m‐, 3‐m‐, 6‐m‐ and 9‐m‐long grass filter strips were setup in a completely randomized block design. During four seasons, masses of dissolved atrazine, metolachlor and deethylatrazine were determined for the first four to five rain events, under natural rain conditions, after atrazine and metolachlor application. Generally, grass filter strips reduced exported herbicide masses by more than 90% and influenced atrazine and metolachlor dissipation kinetics in the field. The 3‐m grass filter strip (area ratio source/strip of 22:1) usually provided a reduction in exported herbicide masses similar to the 6‐ or 9‐m grass filter strips. Therefore, under the present experimental soil and climate conditions, a grass filter strip of 3 m would be a good compromise between environmental protection of surface waters against atrazine and metolachlor contamination and conservation of agricultural land use. Such an approach contributes to the acceptability by producers to implement optimized best management practices such as vegetated filter strips for the preservation of the quality of water resources.  相似文献   

17.
A sensitive method is described for the determination and confirmation of zeranol and zearalenone, as well as their isomers and metabolites, in edible animal tissue. The analytes are extracted from tissue with methanol, hydrolyzed enzymatically, cleaned up by acid-base partitioning, determined by liquid chromatography (LC) with electrochemical (EC) detection, and confirmed by gas chromatography/mass spectrometry (GC/MS). LC analysis is performed by isocratic elution with a buffered mobile phase using a Nova-Pak reverse-phase C18 column with amperometric EC detection at +0.90 V. Capillary GC/MS analysis of the trimethylsilyl derivatives provides mass spectral confirmations.  相似文献   

18.
Structure elucidation of the lilac aldehyde and lilac alcohol stereoisomers was ascertained by (1)H nuclear magnetic resonance (NMR) spectroscopy, including intramolecular nuclear Overhauser effects of the separated diastereoisomers and anisotropic effects of the diastereomeric 2-phenylpropionyl ester, and (1)H, (1)H COSY NMR spectroscopy of synthesized (5'R)-configured stereoisomers, synthesized from (R)-linalool. Direct stereodifferentiation of the eight stereoisomers of lilac aldehyde and lilac alcohol, respectively, has been achieved, using enantioselective capillary GC. The elution order of the isomers was deduced from the chromatographic behavior of the (5'R)-configured diastereoisomers. Additionally, the odor thresholds of lilac aldehyde and lilac alcohol stereoisomers are reported.  相似文献   

19.
One of the most efficient fertilizers to correct Fe deficiency in calcareous soils and waters with high bicarbonate content is based on ferric ethylenediamine-N,N'-bis(o-hydroxyphenylacetic) acid [Fe(o,o-EDDHA)]. Fe(o,o-EDDHA) forms two groups of geometric isomers known as meso and D,L-racemic. To determine the Fe uptake from meso and D,L-racemic Fe(o,o-EDDHA), four iron-efficient plants, two plants representative of strategy I (tomato and pepper) and two plants representative of strategy II (wheat and oats), were grown in hydroponic culture. Results indicated that strategy II plants took up iron from both Fe(o,o-EDDHA) isomers equally. However, strategy I plants took mainly the iron associated with the meso form (the lowest stability isomer).  相似文献   

20.
Metolachlor is one of the most widely used herbicides in the world for controlling weeds. It has been detected in both ground and surface waters in the United States, and there are rising concerns in regard to its health risks and in developing effective treatment processes for its removal from water. Degradation of metolachlor via ultraviolet (UV) photolysis and an UV/hydrogen peroxide advanced oxidation process (AOP) was studied. The quantum yield of metolachlor at 254 nm was found to be 0.302 +/- 0.001 mol E-1 through direct UV photolysis in the range of pH 6-8. The second-order rate constant of the reaction between metolachlor and hydroxyl radical was determined to be 9.07 (+/-0.21) x 10(9) M-1 s-1 by using a competition kinetics model that utilized nitrobenzene as a reference compound. In addition, these parameters were successfully applied in modeling the kinetics of elimination of metolachlor using an UV/H2O2 process in both laboratory and natural waters. The formation of several photolysis byproducts was identified using gas chromatography/mass spectrometry, and a scheme for the metolachlor photodegradation pathway is proposed.  相似文献   

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