Application of Matrix Solid-Phase Dispersion and Liquid Chromatography–Ion Trap Mass Spectrometry for the Analysis of Pesticide Residues in Fruits

This study presents an application of rapid and sensitive multiresidue method for the analysis of acephate, acetamipride, atrazine, carbendazim, carbaryl, carbofuran, dimethoate, imidacloprid, linuron, malathion, monocrotophos, monuron, propazine, simazine, and tebufenozide in fruits. The method involves an extraction procedure based on matrix solid-phase dispersion using diatomaceous earth as a dispersant and dichloromethane as the eluent. The target pesticides were determined using liquid chromatography–ion trap mass spectrometry. Quantification of the analytes was carried out using the most sensitive ion transition. Ion trap parameters, like activation q and time, were found to have a prominent influence on method sensitivity for some pesticides and they were optimized accordingly. The confirmation of residues detected in real samples was performed by repeated injection and acquiring additional ion transitions besides the ones used for quantification. The method was validated for accuracy, linearity, reproducibility, and sensitivity. Mean values for recoveries were in the range of 70–120 % for all tested matrices. Repeatability of the method, expressed as the relative standard deviation, was in general lower than 20 %. The applicability of the method to routine analysis was tested in real fruit samples with good performance.     

Determination of perchlorate in infant formula by isotope dilution ion chromatography/tandem mass spectrometry

A sensitive and selective isotope dilution ion chromatography/tandem mass spectrometry (ID IC-MS/MS) method was developed and validated for the determination of perchlorate in infant formula. The perchlorate was extracted from infant formula by using 20 ml of methanol and 5 ml of 1% acetic acid. All samples were spiked with (18)O(4) isotope-labelled perchlorate internal standard prior to extraction. After purification on a graphitised carbon solid-phase extraction column, the extracts were injected into an ion chromatography system equipped with an Ionpac AS20 column for separation of perchlorate from other anions. The presence of perchlorate in samples was quantified by isotope dilution mass spectrometry. Analysis of both perchlorate and its isotope-labelled internal standard was carried out on a Waters Quattro Ultima triple quadrupole mass spectrometer operating in a multiple reaction monitoring (MRM) negative ionisation mode. The method was validated for linearity and range, accuracy, precision, sensitivity, and matrix effects. The limit of quantification (LOQ) was 0.4 μg l(-1) for liquid infant formula and 0.95 μg kg(-1) for powdered infant formula. The recovery ranged from 94% to 110% with an average of 98%. This method was used to analyse 39 infant formula, and perchlorate concentrations ranging from 相似文献   

Numerical investigation of the drag closure for bubbles in bubble swarms

The present paper describes an Euler–Lagrange model utilizing a drag closure derived from direct numerical simulations (front-tracking model) for (i) single isolated bubbles and (ii) bubbles rising in bubble swarms, expressed as a function of the local gas fraction. The model is applied to the prediction of an air/water system in a bubble column and for which experimental data is available. The effect of variation in size of the mapping window for the interphase coupling between the Eulerian and Lagrangian framework is investigated for both closure relations. It is found that the drag closure as a function of the local gas fraction is an improvement over the use of the drag closure for isolated single bubbles for the prediction of bubbly flow.     

Chromatographic characterisation of aptamer-modified poly(EDMA-co-GMA) monolithic disk format for protein binding and separation

The introduction of aptameric ligands onto disk-monolithic adsorbent, representing a unique strategy for convective isolation of target molecules with high specificity and selectivity, is investigated for the first time. Experimental results showed that the disk monolith possessed a good permeability of 1.67 ± 0.05 × 10^–14 m² (RSD = 3.2%). The aptameric ligand density for the aptamer-modified disk monolith was 480 pmol/uL. Chromatographic analysis of the aptamer disk-monolith efficiency showed an optimum linear velocity of 126 cm/min (≈0.25 mL/min) at room temperatures 25 ± 2°C. The theoretical number of plates corresponding to the optimum linear velocity was 128.2 with an height equivalent to the theoretical plate of 0.022 mm. The disk aptamer-immobilised monolithic system demonstrated good selectivity and isolation of thrombin from non-targets.     

Attenuation of iNOS and COX2 by blueberry polyphenols is mediated through the suppression of NF-κB activation

Treatment of BV2 microglial cells with blueberry extracts has been shown to be effective in reducing lipopolysaccharide (LPS)-induced proinflammatory mediators such as nitric oxide (NO), tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), inducible NO synthase (iNOS), and cyclooxygenase 2 (COX2). The current study explored the possibility that the down-regulation of iNOS and COX2 by blueberry extracts was mediated through NF-κB signaling pathway. A column-purified fraction of polyphenol-enriched blueberry extract (PC18) was used to treat LPS-activated BV2 cells. The results thus far showed that blueberry polyphenols significantly suppressed iNOS and COX2 promoter activities. In addition, blueberry polyphenols inhibited NF-κB nuclear translocation in LPS-activated BV2 cells. These findings suggested that the beneficial effects of blueberries may involve direct modulation of oxidative stress and/or inflammatory signaling cascades.     

COSMO-RS:An ionic liquid prescreening tool for gas hydrate mitigation

Recently ionic liquids(ILs) are introduced as novel dual function gas hydrate inhibitors. However, no desired gas hydrate inhibition has been reported due to poor IL selection and/or tuning method. Trial error as well as selection based on existing literature are the methods currently employed for selecting and/or tuning ILs. These methods are probabilistic, time consuming, expensive and may not result in selecting high performance ILs for gas hydrate mitigation. In this work, COSMO-RS is considered as a prescreening tool of ILs for gas hydrate mitigation by predicting the hydrogen bonding energies(E_(HB)) of studied IL inhibitors and comparing the predicted E_(HB) to the depression temperature(?) and induction time. Results show that, predicted EHBand chain length of ILs strongly relate and significantly affect the gas hydrate inhibition depression temperature but correlate moderately(R = 0.70) with average induction time in literature. It is deduced from the results that, ? increases with increasing IL EHBand/or decreases with increasing chain length. However, the cation–anion pairing of ILs also affects IL gas hydrate inhibition performance. Furthermore, a visual and better understanding of IL/water behavior for gas hydrate inhibition in terms of hydrogen bond donor and acceptor interaction analysis is also presented by determining the sigma profile and sigma potential of studied IL cations and anions used for gas hydrate mitigation for easy IL selection.     

Effect of molecular weight distribution on polymer diffusion during film formation of two-component high-/low-molecular weight latex particles

We describe fluorescence resonance energy transfer (FRET) studies of film formation by a new type of two-component latex particles. These particles consist of a miscible blend of two components that have a similar composition but very different molecular weights. In our approach, we used sequential seeded emulsion polymerization to generate (in situ) a fraction of oligomer in poly(butyl acrylate-co-methyl methacrylate) P(BA-MMA) seed particles that contained a relatively high molecular weight (high-M) dye-labeled polymer. In this way we could systematically change the molecular weight distribution of polymer inside the particles. We varied the amount and the molecular weight of the oligomers. For latex films cast from these two-component particles, we studied the diffusion rate of the high molecular weight polymer by FRET. These measurements revealed that oligomers promoted diffusion rate during latex film formation (oligoplasticization). We analyzed our diffusion data in terms of the Fujita–Doolittle free-volume model and showed that higher molecular weight oligomers are less efficient as plasticizers. In separate experiments, oligomers with similar molecular weights as those in the two-component particles were introduced via latex blending. We compared oligoplasticization in latex blends films with that in the two-component particles films. Finally, we investigated the rheological behavior of the two-component polymers with compositions adjusted to have a common T_g (2 °C). The higher the molecular weight of the oligomer, the more that had to be added to achieve T_g = 2 °C. All of the oligomers were much shorter than the entanglement length and act as diluents of the entanglements in the high-M polymer. We found that incorporating larger amounts of oligomers with a higher molecular weight resulted in a more pronounced drop in polymer viscosity, associated with the decrease in the entanglement density.     

CRITICAL SELF-ASSEMBLY CONCENTRATION OF AN IONIC-COMPLEMENTARY PEPTIDE EAK16-I

Understanding the process of self-assembly of peptides has been important in various biomedical engineering applications. This work focuses on the effect of peptide concentration on the molecular self-assembly of an ionic-complementary peptide, EAK16-I (AEAKAEAKAEAKAEAK), in aqueous solution. The surface tension and self-assembled nanostructures were determined for a wide range of peptide concentrations using axisymmetric drop shape analysis-profile (ADSA-P) and atomic force microscopy (AFM), respectively. Surface tension measurements revealed a critical self-assembly concentration of 0.3 mg peptide/ml water, below which the surface tension decreased rapidly with increasing peptide concentration, and above which the surface tension remained at a constant, plateau value. There were two structural transitions observed with increasing peptide concentration: the first was from globular nanostructures to fibrils, and the second from the fibrils to relatively thick fibers. The second structural transition occurred at the critical self-assembly concentration as determined by the surface tension measurements. The nanostructural behavior of EAK16-I was compared with that of EAK16-II, which has the same amino acid composition but a different charge distribution. Salt effects were also examined by adding NaCl to the peptide solution. The salt addition facilitated the formation of peptide fibrils at low peptide concentrations but increased the critical self-assembly concentration, which occurred at 0.8 mg peptide/ml water in the presence of 20 mM NaCl. The structural transitions involved in the self-assembly of EAK16-I resemble those from protofibrils to fibrils observed with numerous naturally occurring peptides. An understanding of this structural transition may have relevance in the analysis and treatment of peptide/protein conformational diseases and have application in the production of self-assembled protein nanostructures.