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101.
Lina Kantiani Marinella Farré Josep Manuel Grases i Freixiedas Damià Barceló 《Analytical and bioanalytical chemistry》2010,398(3):1195-1205
A fully automated method has been developed for analysis of eighteen antibacterial compounds, including penicillins, cephalosporins
and sulfonamides, in animal feed with limits of quantification in the range 0.25–5.79 μg kg−1. The method is based on pressurized liquid extraction of 3 g homogenized feed with water and online clean-up of 500 μL of
the extract with C18HD cartridges. The purified sample was directly analysed by liquid chromatography–electrospray tandem mass spectrometry (SPE–LC–ESI-MS–MS).
Chromatographic separation was achieved within 10 min by use of a C12 Phenomenex Hydro-RP reversed-phase analytical column and a mobile phase gradient (water + 0.1% formic acid–methanol + 0.1%
formic acid). The method was validated, revealing capability for detection of concentrations as low as 0.09 μg kg−1, decision limits (CCα) and detection capabilities (CCβ) in the range 10–174 μg kg−1 and 22–182 μg kg−1, respectively, and inter-day precision ranging from 0.7 to 8.3%. Recovery, with internal standard correction, was in the
range 93–134% for all analytes. The method was then applied to analysis of fifteen feed samples, nine of which contained at
least one antimicrobial at concentrations between 0.006 and 1.526 mg kg−1. The performance data and results from the method were compared with those from a previous method developed by our group,
using offline SPE, by analyzing the same set of samples by both methods. The online SPE approach resulted in slightly improved
sensitivity, with LODs of 0.09–2.12 μg kg−1 compared with 0.12–3.94 μg kg−1 by the offline approach. In general, better recovery was achieved by use of online purification (for 72% of the analytes)
and the correlation between the two methods was good. The main advantages of the new online method are rapid and automated
sample pre-treatment, and reduction of sample manipulation, enabling high-throughput analysis and highly accurate results.
Because of all these characteristics, the proposed method is applicable and could be deemed necessary within the field of
food control and safety. 相似文献
102.
Xiangyang Wu Dr. Lina Cui Dr. Tomasz Lipinski Dr. David R. Bundle Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(11):3476-3488
Zwitterionic polysaccharides (ZPSs) from Bacteroides fragilis and Streptococcus pneumoniae display unique T‐cell activities. The first synthesis of a hexasaccharide representing two repeating units of the zwitterionic capsular polysaccharide from S. pneumoniae type 1 (Sp1) is reported. Key elements of the approach are stereoselective construction of 1,4‐cis‐α‐galactose linkages based on a reactive trichloroacetimidate donor that incorporates a 6‐O‐acetyl group, which may contribute to the high α selectivity in glycosylation. After assembly of the fully protected hexasaccharide from five monosaccharide synthons 2 – 4 , 24 and 25 , selective deprotection of the primary hydroxyl groups of the four galactose residues followed by oxidation to the corresponding uronic acids provides hexasaccharide 19 . The trisaccharide counterpart 1 was synthesized in similar fashion from three synthons, 2 – 4 . This approach employed both conventional and dehydrative glycosylation methodologies and avoids the use of poorly reactive uronic acid derived glycosyl donors and acceptors. 相似文献
103.
Raudonis R Bumblauskiene L Jakstas V Pukalskas A Janulis V 《Journal of chromatography. A》2010,1217(49):7690-7698
On-line method, which combines HPLC distribution and post-column reaction, was designed for the search of individual antioxidants. Optimization of the assay was performed evaluating optimal ABTS(+) radical cation concentration in the reactor, reaction time, impact of flow rate, reaction coil length. HPLC-ABTS assay validation in this work was performed by assessing reference antioxidant negative peak areas in radical scavenging chromatogram. Sample free radical scavenging activity is expressed as trolox equivalent antioxidant capacity (TEAC). Optimized and validated method was applied in detection of compounds possessing free radical scavenging ability in complex mixtures. Antioxidant compounds were studied in perilla (Perilla frutescens (L.) Britton var. crispa f. viridis) herbal raw material and its preparations. The HPLC-separated antioxidant compounds were identified using HPLC-photodiode array coupled to mass spectrometer, using a reference mass for determining accurate masses. Radical scavenging characteristics of rosmarinic acid, which is the dominant phenolic compound in medicinal herbal raw material of perilla and its preparations, were confirmed by the calculated TEAC values. Compounds responsible for antioxidant effect in herbal raw materials and herbal preparations were identified, evaluated and compared. 相似文献
104.
采用溶胶-凝胶法,将聚(苯乙烯-co-丙烯酸)(PSA)膜材料和氯化镁的复合物包覆在以硅胶为载体的TiCl3催化剂上,负载TiCl4后制得Ziegler-Natta复合催化剂.采用红外光谱、激光粒度仪和扫描电镜对催化剂进行了表征,结果表明该复合催化剂呈核壳结构.同时,考察了复合催化剂中膜的厚度和反应中的氢气含量对催化剂的聚合活性和聚乙烯性能的影响,实验发现,膜厚约为3μm的核壳结构复合催化剂活性良好,其具有带诱导期的平稳型动力学曲线;膜厚1.5μm的复合催化剂的活性接近于实验所用的以硅胶为载体的TiCl3催化剂,且其具有相似的衰减型动力学曲线.研究同时表明,不同的膜厚能够调节复合催化剂的氢调性能及所得聚乙烯的分子量分布. 相似文献
105.
By expanding the Debye theory into the tight focusing of partially coherent field, the intensity and spatial correlation properties of partially coherent radially polarized vortex beams are studied. Expressions are derived for the intensity distribution and the spectral degree of coherence in the focal region. It is found that the intensity and the transverse and longitudinal coherence degrees in the focal region change with the variation of the topological charge and coherence length of the vortex beam. In addition, the degree of coherence is shown to exhibit phase singularities. 相似文献
106.
Lina Guo Jiulin Du 《Physica A》2011,390(2):183-188
The generalized Gibbs free energy and enthalpy are derived in the framework of nonextensive thermodynamics by using the concept of the physical temperature and the physical pressure. Some relations of the thermodynamical potentials are changed due to the difference between the physical temperature and the inverse of Lagrange multiplier. We derive the thermodynamical relation between the heat capacities at a constant volume and at a constant pressure using the generalized thermodynamical potential. We find that it has a different form from the traditional one in Gibbs thermodynamics. But, the expressions of the heat capacities in this framework using the generalized thermodynamical potentials are still the same as the traditional one. 相似文献
107.
利用洛必达法则研究长度趋于零和长度趋于无穷大的两类区间上高阶柯西值定理中间点的渐近性及其误差估计. 相似文献
108.
静电场与涡旋电场无限大平面的电通量 总被引:1,自引:0,他引:1
讨论了静电场和涡旋电场在无限大平面上的电通量。提出了关于涡旋电场无限大平面电通量等于零的假设。 相似文献
109.
Consider the 1+1-dimensional quasi-linear diffusion equations with convection and source term u t =[ u m ( u x ) n ] x + P ( u ) u x + Q ( u ) , where P and Q are both smooth functions. We obtain conditions under which the equations admit the Lie Bäcklund conditional symmetry with characteristic η= u xx + H ( u ) u 2 x + G ( u )( u x )2− n + F ( u ) u 1− n x and the Hamilton–Jacobi sign-invariant J = u t + A ( u ) u n +1 x + B ( u ) u x + C ( u ) which preserves both signs, ≥0 and ≤0, on the solution manifold. As a result, the corresponding solutions associated with the symmetries are obtained explicitly, or they are reduced to solve two-dimensional dynamical systems. 相似文献
110.
Cover Picture: Stabilizing Two Classical Antiaromatic Frameworks: Demonstration of Photoacoustic Imaging and the Photothermal Effect in Metalla‐aromatics (Angew. Chem. Int. Ed. 21/2015) 下载免费PDF全文