On‐line flow‐through extraction–preconcentration‐large volume injection‐RP LC for trace determination of pyrethroids in Slovak soil

A rapid micro‐analytical multiresidue method was developed for analysis of pyrethroids (kadethrin K, cypermethrin C and permethrin P) in soil micro‐sample (200 mg). It uses on‐line flow‐through extraction of soil micro‐samples (packed into a short glass column) with a methanol‐aqueous citric acid buffer mixture, successive on‐line SPE preconcentration of analytes from the extract and on‐line RP‐HPLC analysis with UV photometric detection. The separation of pyrethroids is performed on a Purospher RP‐18e column with methanol/water as mobile phase. Effects of sorbent placed at the bottom of a short column holding the soil sample and different kinds of on‐line SPE columns were tested. Besides, the influence of volume of the effluent on the pyrethroids recovery was also studied. Calibration curves were linear over the range assayed from 0.01 to 0.2 μg/mL with correlation coefficients of linear regression (least‐squares method) in the range 0.998–0.999. Recovery studies were carried out at 0.25–1.00 μg/g dry soil fortification level and obtained recoveries were for K 81–84%, C 56–59% and for P 58–63%. Achieved LOD (confidence band) of studied pyrethroids were for large‐volume injection (1 mL) 4.5 ng K, 3.7 ng C, 3.6 ng P or 27 ng/g K, 32 ng/g C and 29 ng/g P in dry soil “solid sampling HPLC”.     

Ultrasound-assisted dispersive liquid–liquid microextraction for the determination of six pyrethroids in river water

A simple ultrasound-assisted dispersive liquid–liquid microextraction method combined with liquid chromatography was developed for the preconcentration and determination of six pyrethroids in river water samples. The procedure was based on a ternary solvent system to formatting tiny droplets of extractant in sample solution by dissolving appropriate amounts of water-immiscible extractant (tetrachloromethane) in watermiscible dispersive solvent (acetone). Various parameters that affected the extraction efficiency (such as type and volume of extraction and dispersive solvent, extraction time, ultrasonic time, and centrifuging time) were evaluated. Under the optimum condition, good linearity was obtained in a range of 0.00059–1.52 mg L⁻¹ for all analytes with the correlation coefficient (r²) > 0.999. Intra-assay and inter-assay precision evaluated as the relative standard deviation (RSD) were less than 3.4 and 8.9%. The recoveries of six pyrethroids at three spiked levels were in the range of 86.2–109.3% with RSD of less than 8.7%. The enrichment factors for the six pyrethroids were ranged from 767 to 1033 folds.     

Clean-up of some organochlorine and pyrethroid insecticides by automated solid-phase extraction cartridges coupled to capillary GC-ECD

The ASPEC (Automatic Sample Preparation with Extraction Columns) system has been coupled on-line to capillary GC-ECD by means of a loop-type interface equipped with a solvent vapour exit. Both ASPEC and GC conditions have been optimized leading to an effective clean-up of the extracts analyzed. By means of solid-phase extraction cartridges filled with silica, it has been possible to analyze concentrated surface water extracts for a group of 18 electron-capturing compounds present in the water at ppt levels. ASPEC-GC has also been applied to the determination of synthetic pyrethroids at ppt levels in surface water. The complete analytical procedure is greatly facilitated by automation and miniaturization. Miniaturization results in a considerable decrease in the sample volume required. The potential of the method for the analysis of other pesticides is estimated.     

Solid-phase microextraction (SPME) for the determination of pyrethroids in cucumber and watermelon using liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection

A sensitive and efficient solid-phase microextraction (SPME) method for the determination of seven pyrethroid insecticides including fenpropathrin, λ-cyhalothrin, deltamethrin, fenvalerate, permethrin, τ-fluvalinate and bifenthrin in cucumber and watermelon samples using high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (SPME-HPLC-PIF-FD) was developed and validated. The optimum SPME conditions were used for the extraction of samples of both matrices (extraction time 30 min, stirring rate 1100 rpm, extraction temperature 65 °C, sample pH 3, soaking time 7 min, desorption time 5 min, ACN content 25%, desorption and soaking solvent was the mobile phase and in static mode). The method was validated in terms of limits of detection (LODs) and the limits of quantification (LOQs) in both IUPAC and EURACHEM criteria. LODs and LOQs were achieved in values lower than the maximum residue levels (MRLs) established in the Spanish regulations for all pesticides in this study (MRLs range between 0.01 and 0.1 mg kg⁻¹ for all pyrethroid insecticides in both matrices). LOQs according to the second criterion were between 1.5 and 5 μg kg⁻¹ for cucumber; and between 1.3 and 5 μg kg⁻¹ for watermelon samples. Precision and recovery studies were evaluated at two concentration levels for each matrix. Good precision was obtained and relative standard deviation values were less than 10% in all cases. Recovery values were calculated at 0.05 and 0.5 mg kg⁻¹ levels (n = 6) and they ranged between 93% and 108% for cucumber and between 91% and 110% for watermelon samples. Applicability of the method to pyrethroids in cucumber and watermelon of commercial samples was demonstrated.     

拟除虫菊酯类农药的NMR研究——Ⅱ.拟除虫菊酯类中酯键部分构象的NMR研究

利用~1H-NMR中羰基的ASIS值在羰基周围不同的区域符号分布的经验规律,研究了一系列拟除虫菊酯化合物羰基酯键部分的构象,指出在具有α-氰基的菊酯分子中,其溶液态构象是α-氰基与酯羰基共平面的构象,而在个有α-甲基的菊酯分子中,溶液态构象是α-氢原子与酯羰基共平面的构象.本实验结果支持了Hopfinger等人用分子力学方法计算的结果,从而肯定了氰基取代的菊酯分子在溶液态下的构象与在晶体中构象的不同.     

Sorption behaviour of bifenthrin on cork

Biphentrin, a known pyrethroid, was studied, aiming its removal from aqueous solutions by granulated cork sorption. Batch experiments, either for equilibrium or for kinetics, with two granulated cork sizes were performed and results were compared with those obtained with of activated carbon sorption. Langmuir and Freundlich adsorption isotherms were obtained both showing high linear correlations. Bifenthrin desorption was evaluated for cork and results varied with the granule size of sorbent. The results obtained in this work indicate that cork wastes may be used as a cheap natural sorbent for bifenthrin or similar compounds removal from wastewaters.     

Characteristics and enantiomeric analysis of chiral pyrethroids

Pyrethroids are synthetic pesticides that originated from the modification of natural pyrethrins to improve their biological activity and stability. They are a family of chiral pesticides with a large number of stereoisomers. Enantiomers of synthetic pyretroids present different insecticidal activity, toxicity against aquatic invertebrates and persistence in the environment so the development of rapid and sensitive chiral methods for the determination of different enantiomers is necessary. Several techniques have been employed for this purpose including gas chromatography, high performance liquid chromatography or more recently capillary electrophoresis and sub or supercritical fluid chromatography. A general view on the different chiral separation methods applied to the analysis of pyrethroids and the most important information about these pesticides is provided in this review.     

Efficient photochemical synthesis of 2-vinylcyclopropanecarbaldehydes, precursors of cyclopropane components present in pyrethroids, by using the oxa-di-π-methane rearrangement

A comparative study on the triplet photoreactivity of a series of β,γ,δ,?-unsaturated aldehydes 14a-f and 15, using 3-methoxyacetophenone and 4-phenylbenzophenone as sensitizers, has been carried out. When 3-methoxyacetophenone is used as the triplet sensitizer, the aldehydes undergo oxa-di-π-methane rearrangement (ODPM) to afford the corresponding cyclopropanecarbaldehydes 16a-f and 17 in yields ranging from 14% to 62% in addition in most cases to products resulting from decarbonylation. However, when 4-phenylbenzophenone is used as the photosensitizer ODPM products are obtained exclusively in almost quantitative yield. These are additional examples of the recently described, unexpected influence of the nature of the triplet sensitizer on the photoreactivity of organic compounds.     

纳米纤维在分析菊酯类农药残留中的应用

以电纺聚苯乙烯纳米纤维作固相萃取材料,对茶叶样品中的拟除虫菊酯农药进行分离富集,用气相色谱-电子捕获器进行检测,并对影响纤维萃取效率的因素进行优化,联苯菊酯、氯菊酯、氰戊菊酯、溴氰菊酯和甲氰菊酯在纳米纤维柱上的最大吸附量分别为7.8、7.5、7.2、6.6、7.0μg/mg,5种农药的3种标准混合液通过纳米纤维小柱后回收率为65.5%～89.0%,RSD为1.2%～3.0%。测定喷洒5种农药后的茶叶样品添加回收率为61.3%～87.1%,RSD为0.9%～2.8%,方法的测定下限为1.0×10-4～1.0×10-2mg/kg。该方法可以满足茶叶中拟除虫菊酯类农药残留检测的要求。     

Online trace enrichment to determine pyrethroids in river water by HPLC with column switching and photochemical induced fluorescence detection

The potential of online trace enrichment on a highly apolar short column in LC was evaluated for the determination of pyrethroids in river water. Twelve millilitres of water samples, modified with 8 mL ACN (ACN/water 40:60, v/v), were passed through 50 x 4.6 mm ID first separation column packed with 5 microm Hypersil Elite C18. Pesticides were preconcentrated in this column while the matrix background was eluted to waste. Separation of pesticides was performed on a 3.5 microm symmetric C18 column (250 x 4.6 mm ID) with an ACN step gradient as mobile phase and fluorescence detection was used after postcolumn derivatization by using UV light. The use of photochemically induced fluorescence for detection improved sensitivity and selectivity. Quantification limits ranged from 0.05 to 0.1 microg/L and pesticide recoveries at two concentration levels (0.1 and 0.5 microg/L) were between 93.1 and 118.6%, with RSD between 2.5 and 7.5% (n = 3) in river water samples. No matrix effect was detected.