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排序方式: 共有233条查询结果,搜索用时 15 毫秒
161.
Anjos JC Appel JA Bean A Bracker SB Browder TE Cremaldi LM Duboscq JE Elliott JR Escobar CO Gibney MC Hartner GF Karchin PE Kumar BR Losty MJ Luste GJ Mantsch PM Martin JF McHugh S Menary SR Morrison RJ Nash T Pinfold J Punkar G Purohit MV Ross WR Santoro AF Schmidt DM Shoup AL Sliwa K Sokoloff MD Souza MH Sperka D Spalding WJ Streetman ME Stundia AB Witherell MS 《Physical review letters》1991,67(12):1507-1510
162.
Stability of sulfonamides,nitrofurans, and chloramphenicol residues in preserved raw milk samples measured by liquid chromatography 总被引:1,自引:0,他引:1
Noa M Perez N Gutierrez R Escobar I Diaz G Vega S Prado G Urban G 《Journal of AOAC International》2002,85(6):1415-1419
A stability study was made of 10 antimicrobials: 6 sulfonamides, 3 nitrofurans, and chloramphenicol residues in raw milk samples preserved with 0.1 % potassium dichromate (K2Cr2O7) and 0.05% mercuric bichloride (HgCl2) during cold storage for 7 days. Preserved milk samples fortified with 50 ppb of each antimicrobial were analyzed by liquid chromatography (modified AOAC Method 993.32). Drugs were extracted with chloroform-acetone after solvent evaporation residues were dissolved with aqueous sodium acetate buffer solution (0.02M, pH 4.8), and fat was removed with hexane. Sulfonamides and chloramphenicol were detected at 275 nm (UV) by using a gradient system of sodium acetate buffer solution-acetonitrile starting at 95 + 5 (v/v) and finishing at 80 + 20 (v/v). Nitrofurans were detected at 375 nm (UV) isocratically with sodium acetate buffer solution-acetonitrile (80 + 20, v/v). Residues stability was measured through recovery data. Sulfamethoxazole, sulfachloropyridazine, nitrofurazone, furazolidone, and furaltadone residues remained stable in the presence of either preservative for 7 days. Sulfamethazine and chloramphenicol were not affected by K2Cr2O7, but had significant losses (p <0.05) when HgCl2 was used: 26.2 and 13.4%, respectively. Average recoveries of sulfamonomethoxine, sulfamerazine, and sulfathiazole significantly decreased by Day 7, with losses of 17.1, 17.2, and 23.2% for K2Cr2O7, and 23.3, 20.7, and 48.0% for HgCl2, respectively. During 5 days of cold storage all antimicrobials tested, except sulfathiazole, remained stable in milk samples preserved with 0.1 % K2Cr2O7 or 0.05% HgCl2. 相似文献
163.
R. Escobar M. S. García-Domínguez A. Guiraúm F. F. de la Rosa 《Analytical and bioanalytical chemistry》1998,361(5):509-511
A flow injection (FI) chemiluminescence method for the determination of Cr(III) in blood serum, urine and hair samples is reported. It is based on the chromium-catalyzed light emission from the luminol oxidation by hydrogen peroxide. The apparatus consists of an FI system with a flow cell formed by a coiled transparent tube suitable for chemiluminescence detection. The specificity of the method is achieved in presence of EDTA. The detection limit under optimum conditions is 0.01 μg L–1 of Cr(III). Precision and accuracy were evaluated by determining Cr(III) concentrations in urine standards from the National Institute of Standard and Technology (NIST). 相似文献
164.
H. Escobar F. R. Díaz R. S. Ramíarez 《Journal of polymer science. Part A, Polymer chemistry》1976,14(5):1167-1174
New thermally stable polyamides were prepared by low-temperature polycondensation in N,N-dimethylacetamide from perchloro-4,4′-dichloroformylbiphenyl and various aromatic and aliphatic diamines. The polymers were characterized by infrared spectroscopy, elemental analysis, TGA, and DSC and found to show higher thermal stability than other nonchlorinated polyamides. 相似文献
165.
Liquid chromatographic determination of multiple sulfonamides, nitrofurans, and chloramphenicol residues in pasteurized milk 总被引:1,自引:0,他引:1
Perez N Gutierrez R Noa M Diaz G Luna H Escobar I Munive Z 《Journal of AOAC International》2002,85(1):20-24
A rapid and selective liquid chromatographic method was developed to detect 6 sulfonamides, 3 nitrofurans, and chloramphenicol residues in pasteurized milk. The 10 drugs were extracted with chloroform-acetone and the organic phase was evaporated; the residues were dissolved in an aqueous sodium acetate buffer solution 0.02M (pH = 4.8), and the fat was removed by washing with hexane. The aqueous layer was collected, filtered, and injected. The 6 sulfonamides and chloramphenicol were detected at 275 nm ultraviolet (UV) using a gradient system starting with sodium acetate buffer solution-acetonitrile (95 + 5) and finishing with sodium acetate buffer solution-acetonitrile (80 + 20). Nitrofurans were detected at 375 nm (UV) isocratically with sodium acetate buffer solution-acetonitrile (80 + 20). For 50 ppb fortified milk, the average recoveries were (sulfathiazole) 65.52%; (sulfamerazine) 75.36%; (sulfamethazine) 93.94%; (sulfachlorpyridazine) 75.94%; (sulfamethoxazole) 85.18%; (sulfamonomethoxine) 83.45%; (chloramphenicol) 104.17%; (nitrofurazone) 91.81%; (furazolidone) 100.76%; and (furaltadone) 72.38%. Method detection limits ranged from 4 ppb (nitrofurazone) to 16 ppb (sulfamethazine). Some matrix interferences (3-7 ppb) were observed only with sulfonamides. 相似文献
166.
Polymer evolution of a sulfonated polysulfone membrane as a function of ion beam irradiation fluence
Ion beam irradiation was used to modify the surface of a sulfonated polysulfone water treatment membrane. A beam of 25 keV H+ ions with three irradiation fluences (1 × 1013 ions/cm2, 5 × 1013 ions/cm2, and 1 × 1014 ions/cm2) was used for membrane irradiation. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analyses were performed on the virgin and irradiated membranes in order to determine the changes to chemical structure incurred by ion beam irradiation. The results show that some of the sulphonic and CH bonds were broken and new CS bonds were formed after irradiation. Atomic force microscope (AFM) analyses show that membrane roughness decreased after irradiation. A significant increase in flux after ion beam irradiation was also observed, while the amount of cake accumulation on the membrane was decreased after ion beam irradiation. Hydrophobicity, pore size distribution and selectivity of the membrane were not affected by ion beam irradiation. 相似文献
167.
R. Escobar M. S. García-Domínguez A. Guiraúm F. F. de la Rosa 《Fresenius' Journal of Analytical Chemistry》1998,361(5):509-511
A flow injection (FI) chemiluminescence method for the determination of Cr(III) in blood serum, urine and hair samples is
reported. It is based on the chromium-catalyzed light emission from the luminol oxidation by hydrogen peroxide. The apparatus
consists of an FI system with a flow cell formed by a coiled transparent tube suitable for chemiluminescence detection. The
specificity of the method is achieved in presence of EDTA. The detection limit under optimum conditions is 0.01 μg L–1 of Cr(III). Precision and accuracy were evaluated by determining Cr(III) concentrations in urine standards from the National
Institute of Standard and Technology (NIST).
Received: 30 June 1997 / Revised: 16 January 1998 / Accepted: 23 January 1998 相似文献
168.
169.
It is well-known that application of invariant functions in various fields of pure or applied mathematics, physics and computer calculations is certainly of interest. In this paper, we study application of the invariant functions of Lie algebras, named \(\psi \) and \(\varphi \) function, respectively, to contractions of some lower-dimensional Lie algebras, with the goal of contributing to progress in any of these fields, particularly in physics and engineering. 相似文献
170.
Guillermo Rey Gozalo Juan Miguel Barrigón Morillas J. Trujillo Carmona David Montes González Pedro Atanasio Moraga Valentín Gómez Escobar Rosendo Vílchez-Gómez Juan A. Méndez Sierra Carlos Prieto-Gajardo 《Applied Acoustics》2016
Different streets of a city of Spain were randomly selected and analyzed, extracting 135 different urban variables. The urban variables were compared with measured noise levels, and the possible significance in the relationships among them was analyzed. From the variables with a significant correlation, a multiple regression model for urban traffic noise was developed, which allows explaining 63% of the variability of urban noise. In this regression model, only eight of the initial urban variables were included. 相似文献