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31.
An automated spray-and-trap (ST) chromatographic system was constructed for fast and efficient extraction of volatile organic compounds (VOCs) in aqueous samples with the capability to be deployed in the field for unattended continuous monitoring of surface or ground water. This system was built upon a commercial gas chromatograph with full automation capability using self-developed hardware and software. For sample analysis, fine droplets of the aqueous solution were generated in the extraction chamber by pressure expansion of a clean air stream through a spray nozzle. A portion of the VOCs distributed into the gas phase was retained by a multi-sorbent micro-trap kept at ambient temperature. Flash heating of the sorbent trap desorbed the enriched VOCs onto the gas chromatography (GC) with flame ionization detection (FID) for hydrocarbons or electron-capture detection (ECD) for halocarbons. In order to validate the performance of the ST method. it was compared with a more conventional method, i.e., a purge-and-trap (PT), by analyzing a serious of standard solutions containing benzene, toluene, ethylene. and o-, m-xylenes. Using a purge-and-trap method as a reference for complete extraction, the ST method showed less sensitivity. Extraction recoveries are in consistent with Henry's law constants. To test response time the ST-GC-ECD was periodically switched between tap and underground waters. Negligible carry-over of halogenated species and reproducibility better than 2% relative standard deviation (R.S.D.) can be achieved regardless of large concentration difference between the two sources, thus demonstrating applicability of the ST system for on-site monitoring. 相似文献
32.
The Brownian-type molecular dynamics simulation is revisited and applied to study the thermal and geometric properties of four mono- and two polyvalent metallic clusters. For the thermal property, we report the specific heat at constant volume CV and study the solid-liquid-like transition by scrutinizing its characteristic. For the geometric property, we calculate the root mean square relative bond-length fluctuation delta as a function of increasing temperature. The thermal change in delta reflects the movement of atoms and hence is a relevant parameter in understanding the phase transition in clusters. The simulated results for the CV of alkali and aluminum clusters whose ground state structures exhibit icosahedral symmetry generally show one phase transition. In contrast, the tetravalent lead is quite often seen to exhibit two phase transitions, a premelting process followed by a progressive melting. In connection with the premelting scenario, it is found here that those (magic number) clusters identified to be of lesser stability (among other stable ones) according to the second energy difference are clusters showing a greater possibility of undergoing premelting process. This energy criterion applies to aluminum clusters nAl=28 and 38. To delve further into the thermal behavior of clusters, we have analyzed also the thermal variation of deltaT and attempted to correlate it with CV(T). It turns out that the premelting (if exist) and melting temperatures of the smaller size clusters (n less, similar 50) extracted from CV do not always agree quantitatively with that deduced from delta. 相似文献
33.
Wang X Yu JC Yip HY Wu L Wong PK Lai SY 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(10):2997-3004
A novel metal/semiconductor nanocomposite with catalytic and photocatalytic functions has been prepared. The new material consists of highly dispersed platinum (Pt) nanoparticles embedded in a cubic mesoporous nanocrystalline anatase (meso-nc-TiO2) thin film. The porous thin film possesses a narrow pore-size distribution and a large surface area. The diameter of the Pt cluster can be controlled to below 5 nm, and the high dispersion of these clusters gives rise to catalytic activity for the oxidation of carbon monoxide, an important reaction for automobile exhaust treatment. This novel ordered mesoporous Pt/TiO2 nanoarchitecture is also a promising photochemical material, as demonstrated by the photo-driven killing of Micrococcus lylae cells on the film. 相似文献
34.
Single nucleotide polymorphism (SNP) arrays were used to detect chromosomal regions with DNA copy number alterations. Current statistical methods for microarray-based comparative genomic hybridization (array-CGH) analysis generally assume certain relationships among adjacent markers on the same chromosome, and these assumptions may be questionable. For an SNP-array-based CGH study, multiple normal reference SNP arrays were collected. In order to utilize these normal reference SNP arrays, we derived an empirical distribution of signal ratios for each SNP marker. With an assumed threshold value for the overall error rate control and the defined signal ratio ranges for chromosomal amplification and deletion, we proposed a procedure to identify chromosomal alteration regions based on several bootstrapped one-sample t-tests and the false discovery rate control. When we have multiple arrays for different individuals with the same disease, our method can also be used to detect SNP markers for chromosomal alteration regions that are common among these individuals. We applied our method to a published SNP array data set for breast carcinoma cell lines. For an individual with breast cancer, numerous chromosomal alteration regions were identified. Compared to results of previous studies, our method identified more chromosomal alteration regions, with some being implicated in the literature to harbor genes associated with breast cancer. For multiple cancer arrays, our results suggested the existence of common chromosomal alteration regions. However, a high proportion of false positives also indicated that genetic variations among different individuals with breast cancer can be present. 相似文献
35.
A novel chiral stationary phase (CSP) was prepared by immobilizing mono(6A-N-allylamino-6A-deoxy)-perphenylcarbamoylated beta-cyclodextrin onto the surface of silica gel via hydrosilylation. The chromatographic properties of this column were tested with a wide range of structurally diverse racemic compounds and drugs under reverse phases. Separation mechanisms involved are also discussed. 相似文献
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37.
The effect of antimony concentration (C(Sb)/mass%) on the surface tension of molten silicon has been determined with the sessile drop method in the temperature range from 1693 to 1773 K and in the range of the oxygen partial pressure, Po(2), in an Ar atmosphere from 10(-23) to 10(-21) MPa. The results show that the surface tension of molten silicon decreases with increasing Sb concentration in the range of C(Sb)<0.9 mass%, which indicates positive adsorption of Sb in molten silicon and can be fairly described with the Szyszkowski's equation. The maximum decrease rate of surface tension is about 65 mN m(-1) (mass% C(Sb))(-1), and the temperature coefficient of surface tension, (partial differential sigma/ partial differential T)C(Sb), increases with increasing C(Sb). The evaporation of the systems was only observed between the melting points of antimony (904 K) and silicon (1683 K), and the surface tension presents no dependence on measuring time above the melting point of silicon. 相似文献
38.
Kinetic study on the cleavage of N‐phenylphthalimide (NPhPT) in the presence of 0.05 M NH2NH2 and mixed H2O‐CH3CN solvents reveals the occurrence of reaction scheme where A, B, C, C1, An, E, and F represent NPhPT, o‐CO?2C6H4CONHC6H5, o‐CONHNH2C6H4‐ CONHC6H5, N‐aminophthalimide, aniline, o‐CO?2C6H4CONHNH2, and o‐CONHNH2C6H4‐CONHNH2, respectively. But, in the presence of either nonbuffered ?0.20 M NH2NH2 hydrazine buffer of pH ~7.30–8.26 with total buffer concentration ([Buf]T) of >0.02 M, further conversion of F to 2,3‐dihydrophthalazine‐1,4‐dione (DHPD) has been detected depending upon the length of the reaction time (t), the values of [Buf]T, and pH. It has been shown that the rate of conversion of C1 to F is much faster than that of C to C1 which is much faster than that of F to DHPD. The reaction step A → C involves general base (GB) catalysis, while step C → C1 seems to involve specific base–general acid (GA) and GB‐GB catalysis. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 147–161, 2005 相似文献
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40.
Bai JZ Bardon O Blum I Breakstone A Burnett T Chen GP Chen HF Chen J Chen SJ Chen SM Chen Y Chen YB Chen YQ Cheng BS Cowan RF Cui HC Cui XZ Ding HL Du ZZ Dunwoodie W Fan XL Fang J Fero M Gao CS Gao ML Gao SQ Gao WX Gratton P Gu JH Gu SD Gu WX Gu YF Guo YN Han SW Han Y Harris FA Hatanaka M He J He KR He M Hitlin DG Hu GY Hu HB Hu T Hu XQ Huang DQ Huang YZ Izen JM Jia QP Jiang CH Jin Y Jones L Kang SH Kelsey MH Kim BK Lai YF Lan HB Lang PF Lankford A Li F Li J Li PQ Li Q Li RB 《Physical review D: Particles and fields》1995,52(7):3781-3784