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161.
Applied Biochemistry and Biotechnology - The effect of different antibiotics at several concentrations of ampicillin (0–250 mg/L),benzylpenicillin (0–250 mg/L), novobiocine (0–150... 相似文献
162.
T. Lopez M.E. Llanos J. Navarrete I. Schifter P. Salas R. Gomez 《Journal of Sol-Gel Science and Technology》1997,8(1-3):321-325
Mg−Si binary oxides were prepared by the sol-gel method, using magnesium diethoxide and tetraethoxysilane as starting materials.
Mg−Si mixed oxides were prepared at pH3 and 9 at nominal concentrations of 1.3, 4.0, and 6.7 mole% MgO. Density and strength
of the acid sites were determined by pyridine thermal programmed desorption. Comparable Lewis acidity was found in pH3 and
9 preparations. However, when the samples were sulfated with sulfuric acid, strong Bronsted acidity was developed, reaching
a maximum at 6.7 mole% MgO. The strong acidity of sulfated samples was corroborated using the isopropanol decomposition reaction
as catalytic test. Similar conversions are obtained at 100°C on sulfated samples, whereas 260°C are required for non-sulfated
ones. 相似文献
163.
164.
L. A. Gomez Jahn J. J. Kasinski R. J. Dwayne Miller 《Applied Physics A: Materials Science & Processing》1987,43(1):41-46
The compression of the output of a Q-switched, mode-locked Nd:YAG (130 ps, 1.06 m) is reported for a number of different core-size single mode, multimode and polarization preserving fibers at power levels near the damage threshold. In maximizing the energy throughput, the main limitations are dielectric breakdown and nonlinear induced birefringence. Compressed pulse stability is found to depend critically on core size at this power level. An optimized compressor has been obtained capable of compression factors up to 35 (3.7 ps) with peak power in excess of 2 MW. Second-harmonic generation has been observed in polarization preserving fibers. 相似文献
165.
166.
Three procedures are proposed for the determination of trace levels of fluoride in sea-water, based on the formation of aluminium monofluoride in an electrothermal graphite furnace, followed by measurement of its molecular absorption at 227.45 nm. They involve the use of dilution, a matrix modifier, or a matrix modifier and an ion-exchange resin, and are all acceptably sensitive and specific for fluoride. Interferences from cations and anions are removed by a simple 20-fold dilution of the sample. At 10-fold sample dilution, chloride interference can be removed by adding 0.3M ammonium nitrate together with 0.01M aluminium + 0.01M strontium as a matrix modifier. The same matrix modifier is valid for use with 5-fold sample dilution and a cation-exchange step to avoid matrix affects from cations and chloride. The detection limit is about 8-10 ng/ml fluoride and the determination limit is 20 ng/ml. The precision of peak-height measurement at 0.2 mug/ml is 5-7%. 相似文献
167.
J. Gomez G. Blondiaux B. Hakim C. Perrin J. L. Debrun 《Journal of Radioanalytical and Nuclear Chemistry》1992,160(1):153-157
Ubiquitous elements like carbon and oxygen always contaminate surfaces and, therefore, are the soucre of important analytical errors at trace level. Even in the case of radioactivation (with charged particles), where the sample can be etched after irradiation, analytical problems exist. In this work, we show that laser desorption/ablation can efficiently clean surfacaes, in the case of GaAs samples, resulting in better analytical conditions. Under ultra high vacuum, these surfaces remain clean long enough, so that the analysis of carbon and oxygen can be carried out using various nuclear methods, according to the needs of the analyst. 相似文献
168.
F. Garcia Sanchez C. Cruces Blanco A.L. Ramos Rubio M. Hernandez Lopez J.C. Marquez Gomez C. Carnero 《Analytica chimica acta》1988
A sensitive fluorimetric method for teh determination of indole-derivative plant-growth regulators of the auxin group (indole-3-acetic acid, indole-3-butyric acid and indole-3-propanoic acid) is based on their eaction with o-phthaladehyde in concentrated sulphuric acid. The fluorescence spectra of the three derivatives are very similar, but the advantages offered by a three-dimensional plot of the spectra, the synchronous derivative approach and the optimization of experimental variables permit the individual and simultaneous quantitation of mixtures of these compounds at the ng ml-1 level. 相似文献
169.
170.
Jose D. Gomez Mark E. Ridgeway Melvin A. Park Kristofer S. Fritz 《International Journal for Ion Mobility Spectrometry》2018,21(3):65-69
Protein post-translational modifications provide critical proteomic details towards elucidating mechanisms of altered protein function due to toxic exposure, altered metabolism, or disease pathogenesis. Lysine propionylation is a recently described modification that occurs due to metabolic alterations in propionyl-CoA metabolism and sirtuin depropionylase activity. Acrolein is a toxic aldehyde generated through exogenous and endogenous pathways, such as industrial exposure, cigarette smoke inhalation, and non-enzymatic lipid peroxidation. Importantly, lysine modifications arising from propionylation and acroleination can be isobaric – indistinguishable by mass spectrometry – and inseparable via reverse-phase chromatography. Here, we present the novel application of trapped ion mobility spectrometry (TIMS) to resolve such competing isobaric lysine modifications. Specifically, the PTM products of a small synthetic peptide were analyzed using a prototype TIMS – time-of-flight mass spectrometer (TIMS-TOF). In that the mobilities of these propionylated and acroleinated peptides differ by only 1%, a high-resolution mobility analysis is required to resolve the two. We were able to achieve more than sufficient resolution in the TIMS analyzer (~170), readily separating these isobars. 相似文献