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51.
Controlled adsorptive accumulation at the hanging mercury drop electrode enables 0.8–11 × 10?5 M chlordiazepoxide to be quantified by differential-pulse stripping voltammetry with accumulation times of 1–3 min. With 3-min accumulation, the peak current is enhanced 12-fold for 1.0 × 10?7 M chlordiazepoxide compared to the current from differential pulse polarography. The detection limit is 0.9 × 10?9 M for 4-min accumulation. The procedure is applied to spiked human serum after preseparation of the drug on a Sep-Pak C18 cartridge. 相似文献
52.
The present paper is concerned with the problem of weighted best simultaneous approximations in Banach spaces. The weighted best simultaneous approximations to sequences from S- and BS-suns in the Banach space are characterized in view of the Kolmogorov conditions. Applications are provided for weighted best simultaneous approximations from RS-sets and strict RS-sets. Our results obtained in the present paper extend and improve all earlier known results in this direction. 相似文献
53.
M. Dolores Petit Dominguez M. Teresa Sevilla Escribano Jose M. Pinilla Macias Lucas Hernandez Hernandez 《Microchemical Journal》1990,42(3)
A sensitive method for the determination of microamounts of cobalt by ion-exchanger spectrophotometry has been developed. The chromogenic agent, Nitroso-R-Salt (NRS), was loaded on an anionic-exchange resin (Amberlite CG-400). The absorbance of the NRS-cobalt complex on the chelating resin was measured at 508 nm. The best conditions for the preconcentration of cobalt on the resin before the spectrophotometric determination were a pH value of 6, temperature of 80 °C, and heating times of 45 or 90 min for 50 and 400 ml of sample, respectively. The detection limits were 27 ng/ml (50-ml samples) and 1.8 ng/ml (400-ml samples). Interference by other metals was investigated. The method is useful for determination of cobalt in natural waters. 相似文献
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Y. Kudriavtsev A. Hernandez R. Asomoza S. Gallardo M. Lopez K. Moiseev 《Surface and interface analysis : SIA》2017,49(2):145-148
We have performed secondary ion mass spectrometry depth profiling analysis of III–V based hetero‐structures at different target temperatures and found that both the surface segregation and surface roughness caused by ion sputtering can be radically reduced if the sample temperature is lowered to ?150 °C. The depth profiling of ‘frozen’ samples can be a good alternative to sample rotation and oxygen flooding used for ultra‐low‐energy depth profiling of compound semiconductors. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
58.
Christina M. Gonzalez Jeffrey Hernandez Jason G. Parsons Jorge L. Gardea-Torresdey 《Microchemical Journal》2010,96(2):324-329
Selenium (Se) is naturally occurring in the environment and is an essential nutrient in mammals. However, environmental Se can be increased to toxic levels through different industrial practices. The potential adsorption of the Se oxoanions, selenite and selenate, from aqueous solutions onto nanosynthesized MnFe2O4 was investigated using batch techniques and DRC-ICP-MS spectroscopy. The nanomaterial (NM) was laboratory synthesized through slow titration of a mixture of Fe2+ and Mn2+ ions. X-ray diffraction and Scherrer's equation were used to determine the phase of the material and crystallite size, respectively. The effects of pH, reaction time, competitive anions, and the adsorption capacity of the synthesized NM to bind selenite and selenate were investigated. The Langmuir isotherm was used to determine the binding capacity of the NM. Results showed that the phase of the nanomaterial was similar to Jacobsite with a size of 27.5 nm. Results also showed that the sorption of either 100 ppb of selenite or selenate was pH independent in the pH range 2 to 6 and occurred within 5 min of contact time. The introduction of Cl− and NO3− anions individually added to solution had no significant effect on the sorption of either selenite or selenate. However, it was found that the addition of SO42− had a competitive effect only on the sorption of selenate, first seen at 10 ppm and more pronounced at 100 ppm of SO42−. In the presence of 100 ppm of PO43−, the adsorption of selenate decreased to 87% while selenite sorption decreased to 20%. From the Langmuir isotherm equation it was determined that the nano-Jacobsite had a selenite and selenate binding capacity of 6573.76 and 769.23 mg Se/kg of NM, respectively. 相似文献
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David Ariza-Ruiz Chong Li Genaro López-Acedo 《Journal of Mathematical Analysis and Applications》2014
We give a direct proof of Schauder's fixed point theorem in the setting of geodesic metric spaces, generalizing the classical Schauder's theorem and improving a recent version of this theorem in CAT(κ) spaces. As an application we prove an existence result for a variational inequality in the setting of CAT(κ) spaces. 相似文献