Search

A simple, rapid and efficient ionic liquid based on dispersive liquid-phase microextraction (IL-DLPME) method was developed for the determination of three triazine and two phenylurea herbicides in water samples. IL (1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]) that dispersed completely into the water solution under controlled temperature was used as the extraction solvent. The analytes were easily concentrated into the ionic liquid phase. This technique combined the process of extraction and concentration of the analytes into one step and avoided use of the more common, toxic organic solvents. The factors affecting the extraction efficiency such as the IL volume, sample pH, extraction time, centrifugal time, dissoluble temperature and ionic strength were optimized. The extracts were analyzed by high-performance liquid chromatography (HPLC) coupled with diode array detector (DAD). Under the optimized conditions, recoveries (50.5–109.1%) were obtained for the target analytes in water samples. The calibration curves were linear and the correlation coefficient ranged from 0.9947 to 0.9973 in the concentration levels of 5–100 μg L−1. The relative standard deviations (RSDs, n = 5) were 6.80–10.78%. The limit of detections (LODs) for the five polar herbicides were between 0.46 μg L−1 and 0.89 μg L−1. [ABSTRACT FROM AUTHOR]

Organophosphate (OP) pesticides are used globally today, to control a wide range of insect pest species in agriculture, homes, and gardens, as well as in veterinary practice. OP pesticide residues in crops, food and food by-products are both a health and international trade issue. At present, QuECHER, matrix solid phase dispersion (MSPD), gel permeation chromatography (GPC), SPE, GC-FPD, GC-NPD, GC-MS, HPLC-MS, and other methods are widely used to detect OP pesticides residue in food. New issues at China Agricultural University (CAU) such as molecular imprinting, matrix effects, storage stabilities and chiral separation of OP pesticides are addressed in this article. [ABSTRACT FROM AUTHOR]

A method based on matrix solid-phase dispersion (MSPD) and liquid chromatography–electrospay ionization–mass spectrometry used to analyze fifteen fungicide residues in fruits and vegetables is described. The method required only 0.5 g of sample, C18-bonded silica was used as dispersant sorbent, and ethyl acetate was used as eluting solvent. Fortified recoveries in apple, orange, banana, lettuce, grape and tomato samples ranged from 71% to 102% and relative standard deviations were less than 13% with fortified levels of 0.03–1.5 mg kg−1. Detection and quantification limits were 1~30 μg kg−1 and 4~100 μg kg−1, respectively, with linear calibration curves extending up to 15 mg kg−1. The analytical characteristics of MSPD compared very favorably with those found for a classical multiresidue method: the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. The method was applied to determine the fungicides in real samples. Liquid chromatography–tandem mass spectrometry (LC–MS–MS) was used as confirmatory tool for positive samples. [ABSTRACT FROM AUTHOR]

The article discusses an alternative strategy of electrode design to optimize the redistribution of acid within the electrode. It is noted that the electrode architecture demonstrates enhanced electrochemical performance of oxygen reduction within the phosphoric acid phase, resulting in a 28% enhancement of the maximum power density for the optimally designed electrode as cathode.

A 3D graphene oxide/carbon sphere supported silver composite (Ag/GO/C) was synthesized using graphene oxide as the reducing agent. The reducing process of Ag+ was monitored by the ultra violet-visible (UV-vis) absorption spectrometer and the physical properties of the Ag/GO/C composite were characterized by Fourier transform infrared spectrometer (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the dispersive Ag nanoparticles are anchored uniformly on the surface of GO sheets with a mean size of about 6.9 nm. With introducing carbon black, the Ag nanoparticles aggregated slightly. Compared with its counterpart Ag/GO, the Ag/GO/C composite showed a significantly enhanced activity towards the oxygen reduction reaction in alkaline media. The enhancement can be ascribed to the 3D composite support, which not only improves the electrical conductivity, but also enforces the mass transport in the catalyst layer facilitating the reactants access to the active sites. Moreover, the Ag/GO/C composite exhibits good tolerance to alcohols, carbonates and tetramethylammonium hydroxide. This work is expected to open a new pathway to use GO as a reducing agent to synthesize electrocatalysts without surfactants. [ABSTRACT FROM AUTHOR]

A rapid and effective alternative analytical method for residues of butachlor in water, soil, and rice was established. The operating variables affecting performance of this method, including different extraction conditions and cleanup adsorbents, were evaluated. The determination of butachlor residues in soil, straw, rice hull, and husked rice was performed using GC/MS after extraction with n-hexane and cleanup with graphite carbon black. The average recoveries ranged from 81.5 to 102.7%, with RSDs of 0.6-7.7% for all of the matrixes investigated. The limits of quantitation were 0.05 mg/kg in water and rice plant, and 0.01 mg/kg in soil, straw, rice hull, and husked rice. A comparison among this proposed method, the conventional liquid-liquid extraction, the Quick, Easy, Cheap, Effective, Rugged, and Safe method, and Soxhlet extraction indicated that this method was more suitable for analyzing butachlor in rice samples. The further validation of the proposed method was carried out by Soxhlet extraction for the determination of butachlor residues in the husked rice samples, and the residue results showed there was no obvious difference obtained from these two methods. Samples from a rice field were found to contain butachlor residues below the maximum residue limits set by China (0.5 mg/kg) and Japan (0.1 mg/kg). The proposed method has a strong potential for application in routine screening and processing of large numbers of samples. This study developed a more effective alternative to the conventional analytical methods for analyzing butachlor residues in various matrixes. [ABSTRACT FROM AUTHOR]

Carbon-supported Ni(OH)2⚊MnOx/C composite was synthesized by reducing the amorphous MnO2/C suspension in the presence of Ni2+ with NaBH4. The electrocatalytic activity and stability toward the oxygen reduction reaction (ORR) in alkaline media as well as the physical properties before and after the accelerated aging tests for the Ni(OH)2⚊MnOx/C composite were investigated and compared with those for the MnOx/C and the amorphous MnO2/C through electrochemical techniques, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The Ni(OH)2MnOx/C composite is more active toward the ORR than the MnO2/C and MnOx/C, especially at low overpotentials, with the half-wave potential shifting positively about 0.05 V. Experienced the accelerated aging tests, the ORR limiting current for the Ni(OH)2⚊MnOx/C composite just degrades a little, while for the MnO2/C and MnOx/C the ORR limiting currents decrease significantly. Though the more obvious negative shifting of the ORR half-wave potential, the Ni(OH)2⚊MnOx/C composite still processes higher current than those for the MnO2/C and MnOx/C in the mixed kinetic-diffusion control region. After the accelerated aging tests, the electron transfer number of the ORR for the Ni(OH)2⚊MnOx/C composite still closes to four, while for the MnO2/C and MnOx/C, the electron transfer numbers decrease obviously from 3.88 and 3.87 to 3.22 and 3.55, respectively. The results of XRD show that phase transformation for Mn occurs and XPS studies prove that the average valence of Mn decreases for both of the MnO2/C and MnOx/C samples after the accelerated aging tests, but no obvious change occurs for the Ni(OH)2-MnOx/C sample. The TEM images before and after accelerated aging tests show that the morphology of the Ni(OH)2-MnOx/C keeps unchanged loosely-aggregated floccules, while for the MnO2/C and MnOx/C, the morphology changes from the initial loosely-aggregated floccules and nano-rods to nano-blocks and some branch-like substances, respectively. The addition of Ni(OH)2 into MnOx plays a significant role in its stabilization. [ABSTRACT FROM AUTHOR]