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A gas chromatographic method was developed for the determination of low-molecular-weight carboxylic acids in aqueous samples based on a derivatization procedure compatible with aqueous solutions. The technique uses nitrogen-selective detection with a thermionic-specific detector after derivatization of carboxylic acids as 2- nitrophenylhydrazides. The hydrazides were extracted with ethyl acetate prior to injection into the gas chromatograph. The derivatives appear to be stable in ethyl acetate at 0–5° C for long periods and, therefore, can be stored for analysis at a later date. The detection limits of different short-chain acids are in the range 0.8–1.4 pmol per injected sample. The relative standard deviation is less than 10% at the 1 μM level. Examples of the use of the method are given for the determination of carboxylic acids in anoxic marine sediment pore waters, coastal sea water and Black Sea water samples. 相似文献
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Derivatization with 2,2′-dithiobis(5-nitropyridine) (DTNP) was used to stabilize thiols in field samples and to determine these compounds by liquid chromatography (LC) with ultraviolet detection. Alternatively, the thiols can be regenerated from DTNP derivatives using tributylphosphine (TBP) and derivatized with o-phthalaldehyde (OPA). The DTNP derivatives were stable at pH 5 and 6 for more than 2 weeks in the reaction mixture, but the stability was considerably lower at pH values > 8. Derivatization at pH 6 was routinely done and the reaction was complete within 5 min. The derivatives can be extracted quantitatively on commercial C18 cartridges, which allows several-fold sample enrichment. The cartridge-adsorbed derivatives are stable at 0–5 °C for long periods and, therefore, can be stored for LC separation at a later date. DTNP derivatives of ten low-molecular-weight thiols were separated on a C18 microbore column using gradient elution and a flow-rate of 200 μl min?1. The relative standard deviation based on repeated analyses of standards is about 5% in the range 0.5–2 nM. Without C18 cartridge enrichment, the detection limits of the studied thiols are in the range 50–100 nM. These limits are further reduced by about 100-fold by using the OPA method after regeneration of thiols from the DTNP derivatives using TBP. Applications of the method to coastal sediment pore water and anoxic Black Sea water are illustrated. 相似文献
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O. A. Chuvenkova E. P. Domashevskaya S. V. Ryabtsev D. V. Vysotskii A. E. Popov Yu. A. Yurakov O. Yu. Vilkov R. Ovsyannikov N. Appathurai S. Yu. Turishchev 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2014,8(1):111-116
Wire-like micro- and nanocrystals of SnO2 are obtained via gas-transport synthesis. The specifics of the atomic and electronic structure of an array of SnO2 wire-like crystals is revealed using near-edge X-ray absorption and X-ray photoelectron spectra. The method of photoemission electron microscopy with high-intensity synchrotron (undulator) radiation is used to study the morphology of SnO2 wire-like crystals for the first time. 相似文献
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E. P. Domashevskaya V. A. Terekhov S. Yu. Turishchev D. A. Koyuda N. A. Rumyantseva Yu. P. Pershin V. V. Kondratenko N. Appathurai 《Physics of the Solid State》2013,55(3):634-641
This paper presents the results of the investigation of c-Si/[Si/Mo] n /Si multilayer nanoperiodic structures by X-ray absorption near-edge structure (XANES) spectroscopy using synchrotron radiation. Changes in the fine structure of XANES MoL 2,3 spectra confirm the formation of the silicide phase on heterophase interfaces Si/Mo/Si due to the solid-phase interactions between silicon and molybdenum layers. 相似文献
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Hartman T Juranić PN Collins K Reilly B Appathurai N Wehlitz R 《Physical review letters》2012,108(2):023001
We have measured the ratio of doubly to singly charged parent ions of benzene, naphthalene, anthracene, and pentacene using monochromatized synchrotron radiation up to 30 eV above the corresponding threshold. Our measurements show a striking similarity between the ratio of doubly charged to all parent ions and the ratio for helium. Moreover, the magnitudes of the ratios for these molecules scale linearly with their lengths with an amazing accuracy. A high ratio, i.e., a high relative double-photoionization probability, makes a molecule an important source of low-energy electrons that can promote radiation damage of biomolecules [B. Bouda?ffa et al., Science 287, 1658 (2000)]. 相似文献
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