The polyphenolic profiles and antioxidant effects of Agastache rugosa Kuntze (Banga) flower,leaf, stem and root

Agastache rugosa Kuntze (Korean mint) is used as a spice and in folk medicine in East Asia. The present study identified a total of 18 polyphenols from the flower, leaf, stem and roots of this plant using high‐performance liquid chromatography–tandem mass spectrometry. Fourteen of these compounds had not previously been identified in these plant tissues. Each polyphenol was validated in comparison with external calibration curves constructed using structurally related compounds, with determination coefficients >0.9993. The limits of detection and quantification were 0.092–0.650 and 0.307–2.167 mg/L, respectively. Recoveries of 61.92–116.44% were observed at two spiking levels, with 0.91–11% precision, expressed as relative standard deviation (except anthraquinone spiked at 10 mg/L). Hydroxycinnamic acid was the most abundant compound in the root, while the flowers showed the highest total flavonoid level. Antioxidant activities, determined in terms of reducing power, Fe²⁺ chelating activity and the radical scavenging activities using α,α‐diphenyl‐β‐picrylhydrazyl and 2‐2?‐azino‐bis‐3‐ethylbenzothiazoline‐6‐sulfonic acid, increased in a concentration‐dependent manner; the highest activity was identified in the stems, followed by leaves > flowers > roots. These findings indicate that A. rugosa is a good source of bioactive compounds and can be used as a functional food. Copyright © 2015 John Wiley & Sons, Ltd.     

Residual determination and risk assessment of buprofezin in plum (Prunus domestica) grown in open‐field conditions following the application of three different formulations

This study was conducted to characterize the residual level and perform a risk assessment on buprofezin formulated as an emulsifiable concentrate, wettable powder, and suspension concentrate over various treatment schedules in plum (Prunus domestica). The samples were extracted with an AOAC quick, easy, cheap, effective, rugged, and safe, ‘QuEChERS’, method after major modifications. As intrinsic interferences were observed in blank plum samples following dispersive‐solid phase extraction (consisting of primary secondary amine and C₁₈ sorbents), amino cartridges were used for solid‐phase extraction. Analysis was carried out using liquid chromatography with diode array detection and confirmed by liquid chromatography–tandem mass spectrometry. The method showed excellent linearity with determination coefficient (R² = 1) and satisfactory recoveries (at two spiking levels, 0.5 and 2.5 mg/kg) between 90.98 and 94.74% with relative standard deviation (RSD) ≤8%. The limit of quantification (0.05 mg/kg) was considerably lower than the maximum residue limit (2 mg/kg) set by the Codex Alimentarius. Absolute residue levels for emulsifiable concentrates were highest, perhaps owing to the dilution rate and adjuvant. Notably, all formulation residues were lower than the maximum residue limit, and safety data proved that the fruits are safe for consumers. Copyright © 2016 John Wiley & Sons, Ltd.     

Magnetic molecularly imprinted specific solid‐phase extraction for determination of dihydroquercetin from Larix griffithiana using HPLC

The naturally occurring quercetin flavonoid, dihydroquercetin, is widely distributed in plant tissues and has a variety of biological activities. Herein, a magnetic molecularly imprinted solid‐phase extraction was tailor made for selective determination of dihydroquercetin in Larix griffithiana using high‐performance liquid chromatography. Amino‐functionalized core‐shell magnetic nanoparticles were prepared and characterized using scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, and infrared spectroscopy. The polymer had an average diameter of 250 ± 2.56 nm and exhibited good stability and adsorption for template molecule, which is enriched by hydrogen bonding interaction. Multiple factors for extraction, including loading, washing, elution solvents, and extraction time, were optimized. The limit of detection was 1.23 μg/g. The precision determined at various concentration of dihydroquercetin was less than 4% and the mean recovery was between 74.64 and 101.80%. It has therefore been shown that this protocol can be used as an alternative extraction to quantify dihydroquercetin in L. griffithiana and purify quercetin flavonoid from other complex matrices.     

Multiresidue analysis of pesticides with hydrolyzable functionality in cooked vegetables by liquid chromatography tandem mass spectrometry

It would be preferable for pesticide residues substituted by hydrolyzable functionality to be analyzed after cooking because their structures are apt to degrade during boiling and/or heating. A liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method for the quantitative determination of 44 pesticide residues with hydrolyzable functional group in five typical vegetable widely consumed in Republic of Korea is described. The sample clean‐up was carried out according to the method of Food Code No. 83 established by the Korea Food and Drug Administration (KFDA). Zorbox XDB‐C₁₈ column was selected for the analysis because of the best peak separation. The LC mobile phase consisted of water and 5 mm methanolic ammonium formate, which resulted in a peak shape with good symmetry at each run. Tandem mass spectroscopic (MS/MS) experiments were performed in ESI positive mode and the multiple reaction monitoring modes. A conventional matrix effect was modified to more comprehensive form 100γ_ij (%). A high matrix effect (相似文献   

无箔二极管电流电压关系研究

本文给出了无箔二极管物理特性的数值模拟研究结果。研究得到了二极管电流与二极管结构参数、二极管电压以及外加磁场强度等参数的变化关系特性，并且应用这些关系特性得到了在外加磁场强度足够大情况下二极管电流的近似表达为Ib=(7.5/x)(x+(0.81-x)/(1+0.7Ld2/δr))(r2/3-1)3/2，其中Ld为阴阳极间距；Rc为阴极发射端面的外半径；Rp为漂移管管壁半径；x=ln(Rp/Rc)，δr =Rp-Rc。这一表达式在大量二极管结构参数和二极管电压参数情况下与数值模拟结果在10％误差范围内相一致，能够比较准确的表达无箔二极管的电流电压关系。     

Melidianolic acid A and B, new antimalarial acyclic diterpenes from Aphanamixis grandifolia

Two new acyclic diterpenes, melidianolic acids A (1) and B (2), have been isolated from the bark of Aphanamixis grandifolia. Their structures were elucidated on the basis of spectroscopic and chemical methods. Melidianolic acids A (1) and B (2) showed antimalarial activity against Plasmodium falciparum 3D7 with IC50 of 6.1 and 7.3 microg/mL, respectively.     

纳米晶Fe73.5Cu1Nb3Si13.5B9晶间非晶相结构弛豫与模量的振荡变化

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Co SiO2颗粒膜的巨磁电阻效应

采用离子束溅射方法在玻璃基片上制备了一系列的Co－SiO\-2颗 粒膜样品,并对样品的巨磁电阻效应进行了研究.在Co35(SiO\-2)65(体积 百分比)颗粒膜样品中,观测到室温下近4%的巨磁电阻效应.研究了不同基片温度对巨磁电 阻效应的影响并发现,随着基片温度的升高样品的巨磁电阻效应下降.根据样品的电阻率温度关系曲线分析,在铁磁金属- 非磁绝缘介质颗粒膜中,除了电子自旋相关隧穿效应外, 可能还存在其他的导电机制. 关键词：     

Simple extraction method using syringe filter for detection of ethephon in tomatoes by negative‐ion mode liquid chromatography with tandem mass spectrometry

In this study, a simple, rapid, and sensitive method was developed for the extraction of ethephon from homogenized tomatoes that does not require a cleanup procedure. In a syringe filter, three distinct layers – aqueous, acetonitrile, and n‐hexane – are clearly separated after storage at ?80 °C for 5–10 min. A Dionex IonPac column was used to separate the analyte before detection using negative‐ion mode liquid chromatography with tandem mass spectrometry (LC/MS/MS). The matrix effect of the tested analyte was negligibly small and the matched calibration showed a good linearity over a concentration range of 0.01–1.0 mg/kg with a correlation coefficient (R²) of 0.9998. The recovery at three fortification levels (0.1, 0.5 and 1.0 mg/kg) was between 82.9 and 108.6% with relative standard deviations (RSDs) <5.0%. The limit of quantification (0.03 mg/kg) was lower than the maximum residue limit (3 mg/kg) set by the Ministry of Food and Drug Safety, Republic of Korea. From a field trial, the method developed herein was applied to calculate the decline pattern and predict the pre‐harvest residue limits of ethephon in tomatoes. In conclusion, the proposed sample preparation is feasible for the detection of hydrophilic analytes in tomatoes. Copyright © 2015 John Wiley & Sons, Ltd.     

Residual detection of naproxen,methyltestosterone and 17α‐hydroxyprogesterone caproate in aquatic products by simple liquid–liquid extraction method coupled with liquid chromatography–tandem mass spectrometry

In the present study, we aimed to develop a reliable screening method based on liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) for the detection and quantification of naproxen, methyltestosterone and 17α‐hydroxyprogesterone caproate residues. The target analytes were extracted from samples of eel, flatfish and shrimp using acetonitrile with 1% acetic acid, followed by liquid–liquid purification with n‐hexane. Chromatographic separation was achieved on a reversed‐phase analytical column using 0.1% formic acid containing 10 mm ammonium formate in distilled water (A) and methanol (B) as mobile phases. All the matrix‐matched calibration curves were linear (R² ≥ 0.99) over the concentration range of the tested analytes. Recovery at three spiking levels (0.005, 0.01 and 0.02 mg/kg) ranged from 68 to 117% with intra‐ and inter‐day precisions <10%. Five market samples for each matrix (eel, flatfish and shrimp) were collected and tested for method application. In summary, the proposed method is feasible to screen and quantify the analytes with high selectivity in aquatic food products meant for human consumption.