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排序方式: 共有311条查询结果,搜索用时 140 毫秒
81.
82.
J. Chico A. Rúbies F. Centrich R. Companyó M. D. Prat M. Granados 《Analytical and bioanalytical chemistry》2013,405(14):4777-4786
An analytical method for determination and confirmation of nine coccidiostatics in eggs is reported. Ethyl acetate is used as extraction solvent, with satisfactory results, and simple automated clean-up is based on gel-permeation chromatography (GPC) . The target compounds are then analysed by liquid chromatography–electrospray ionization–tandem mass spectrometry. The method was validated in-house in accordance with Commission Decision 2002/657/EC. Trueness and precision were determined at four concentrations, and the mean errors obtained were <10 %, with relative standard deviations ranging from 3 to 18 %. For three non-authorized coccidiostatics (clopidol, ethopabate, and ronizadole), decision limit and detection capability were in the ranges 0.12–0.16 and 0.18–0.23 μg kg?1, respectively. The results obtained prove the suitability of this new analytical method for routine monitoring of these substances in eggs. 相似文献
83.
Dr. Albert Granados Dr. Iván Rivilla Prof. Fernando P. Cossío Prof. Adelina Vallribera 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(35):8214-8218
A highly enantioselective catalytic method for the synthesis of quaternary α-trifluoromethyl derivatives of 3-oxo esters is described. The reaction uses lanthanum(III) triflate and chiral PyBOX-type C2-symmetric ligands to generate intermediate LaIII complexes that incorporate an enolate moiety of the starting 3-oxo ester and the trifluoromethylation transfer reagent. The enantioselectivity of the reaction stems from the efficient blockage of one of the prochiral faces of the LaIII enolate by one unit of the C2-symmetric ligand. 相似文献
84.
C. Genest J. J. Quesada Molina J. A. Rodríguez Lallena C. Sempi 《Journal of multivariate analysis》1999,69(2):193
The notion of quasi-copula was introduced by C. Alsina, R. B. Nelsen, and B. Schweizer (Statist. Probab. Lett.(1993), 85–89) and was used by these authors and others to characterize operations on distribution functions that can or cannot be derived from operations on random variables. In this paper, the concept of quasi-copula is characterized in simpler operational terms and the result is used to show that absolutely continuous quasi-copulas are not necessarily copulas, thereby answering in the negative an open question of the above mentioned authors. 相似文献
85.
J. Raich-Montiu J. L. Beltrán M. D. Prat M. Granados 《Analytical and bioanalytical chemistry》2010,397(2):807-814
The extraction of six sulfonamides (sulfadiazine, sulfadimidine, sulfathiazole, sulfachloropiridazine, sulfadimethoxine, and
sulfaquinoxaline) from soils with different physicochemical characteristics and at several aging times was investigated. Conventional
mechanical shaking, microwave-assisted extraction, ultrasound probe-assisted extraction and pressurized liquid extraction
techniques were evaluated. The four techniques provided similar results when applied to freshly contaminated soils. However,
microwave-assisted extraction was the most suitable to extract sulfonamide aged residues from soils. Microwave-assisted extraction
was applied to eight soils aged for 3 months, using acetonitrile:buffer pH 9 (20:80) as the extraction solvent, and recoveries
ranged from 15–25% for STZ to 42–64% for SDM. 相似文献
86.
87.
Granados AM Kreiker J de Rossi RH Fuertes P Torroba T 《The Journal of organic chemistry》2006,71(2):808-810
[reaction: see text] Tricyclic 4-ethyl-5-thioxo-3H,5H-bis[1,2]dithiolo[3,4-d][4,3-b]pyrrol-3-one and monocyclic 3H-1,2-dithiole-3-thione derivatives reacted with Fischer carbene complexes, giving 1,3-dithiin dithioortho esters through insertion of the carbenic carbon into the S-S bond next to the thiocarbonyl function of the substrate. 相似文献
88.
Fernández-Ruiz R Galisteo FC Larese C Granados ML Mariscal R Fierro JL 《The Analyst》2006,131(4):590-594
A methodology for the quantitative analysis of the elements present in car exhaust catalysts by TXRF is described. Some of the most relevant catalytic components (Zr, Rh, Pd) and contaminant elements (P, Pb, Zn, Pt, Ca and Ni) on car Three Way Catalysts were quantified during vehicle aging. The study was conducted along the main axis of a Ford Focus 1.6i catalytic cartridge, aiming to obtain the axial profile of the elements retained or eliminated after more than 59,000 km. The analysis of a fresh Three Way Catalysts (0 km) was also conducted for comparative purposes. The existence of a strong differences for elemental concentration in the interphase between the two blocks of the catalytic cartridge has been quantitatively measured for first time. In addition, the behaviour of the contaminant absorption capacity of both catalytic blocks has been obtained. Finally, the loss of the contaminant elements Pb and Zn to the environment has been proven. 相似文献
89.
J. Fernndez-Ochoa J. Martínez-Moreno J.M. Quesada 《Journal of Approximation Theory》2006,140(2):147-153
Let hp, 1<p<∞, be the best ℓp-approximation of the element from a proper affine subspace K of , hK, and let denote the strict uniform approximation of h from K. We prove that there are a vector and a real number a, 0a1, such thatfor all p>1, where with γp=o(ap/p). 相似文献
90.
Mata-Granados JM Caballo-López A Luque de Castro MD Quesada JM 《Analytical and bioanalytical chemistry》2003,377(2):287-292
An almost automated method for the determination of hydroxymetabolites of vitamin D3 (cholecalciferol) in human serum is reported. The method consists of three steps: 1) a batch liquid–liquid extraction step with 2-propanol and hexane, and drying of the extract and reconstitution with phosphate buffer. 2) A cleanup and preconcentration step based on solid-phase extraction using Prospekt equipment, with CN group cartridges and elution with the chromatographic mobile phase. 3) A chromatographic step for individual separation of the target analytes starting with a 90:10 methanol–water mixture, then a linear gradient to obtain 100% methanol; followed by photometric detection. The method provides a linear range between 1.0 and 100 ng mL–1 for 24,25-(OH)2 vitamin D3 and for 25-(OH)2 vitamin D3, and between 1.5 and 100 ng mL–1 for 1,25-(OH) vitamin D3, with correlation coefficients ranging between 0.993 and 0.987, repeatability between 1.9% and 4.8% and within-laboratory reproducibility between 2.8% and 8.8%. 相似文献