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排序方式: 共有102条查询结果,搜索用时 31 毫秒
1.
Viorica Lopez-Avila Richard Young Werner F. Beckert 《Journal of separation science》1997,20(9):487-492
This paper describes the extraction of 49 organophosphorus pesti-cides (OPPs) from water samples using solid-phase microextraction (SPME). Three fibers, including a 15-μm XAD-coated fiber, a 85-μm polyacrylate-coated fiber, and a 30-μm polydimethylsilox-ane-coated fiber (PDMS), were evaluated here. The effects of stirring and the addition of NaCl to the sample were examined for the polyacrylate-coated fiber. The precision of the technique was examined for all three fibers and the extraction kinetics were investigated using the XAD- and polyacrylate-coated fibers. With some exceptions, the XAD- and polyacrylate-coated fibers performed better than the PDMS-coated fiber. The superiority of the XAD-nd polyacrylate-coated fiber. The superiority of the XAD- and polyacrylate-coated fibers over the PDMS-coated fibers can be attribuibuted to the aromatic functionalities of the XAD and the polar functionalities in the polyacrylate. The relatively high percent RSDs indicate that the SPME technique needs to be further refined before it can be used for anything other than screening. A more effective form of agitation than mechanical stirring may be neccessary to reduce variability and achieve a faster equilibrium between the sample and the SPME fiber. 相似文献
2.
Viorica Lopez-Avila Janet Benedicto Emi Baldin Werner F. Beckert 《Journal of separation science》1992,15(3):160-164
Nineteen halogenated and/or nitrated diphenyl ethers (currently listed in EPA Method 8111) have been separated on a DB-5/ DB-1701 column pair connected to an inlet splitter and separate electron capture detectors. Retention times are included for 10 additional compounds evaluated for their suitability as internal standards or surrogate compounds for incorporation into Method 8111. Method reproducibility and linearity are discussed, and results are presented for extracts of two real samples spiked with the 19 diphenyl ethers and analyzed using the dual-column dual-detector arrangement. 相似文献
3.
Simultaneous detection with a 700-A Hall? and an NPD detector is an effective technique for characterizing chloro-and chloronitroanilines in highly complex Publicly Owned Water Treatment Works (POTW) sludges. The utilization of a modified Varian effluent splitter and a SE-54 fused silica capillary column permitted the detection of mid-picogram quantities of the polar chloroanilines without sacrificing peak shape. The response of the Hall? detector in the halogen mode was roughly proportional to the number of chlorine atoms present, while the response of the Hall? in the nitrogen mode and the NPD was less predictably influenced by the presence of one or more nitro groups. When combined with retention time data, the ratio of the NPD response to the Hall? response has been found to substantiate the presence of chloro- and chloronitroanilines in sludge extracts. 相似文献
4.
The use of four dithiocarbamates and three fluorinated β-diketones as potential chelating agents for three transition metal ions (Cd2+, Pb2+, and Hg2+) extracted from spiked sand and filter paper samples by supercritical fluid extraction (SFE) was investigated. The extractions were performed at 45°C and 250 atm for spiked sand samples and at 60°C and 200 atm for filter paper samples using supercritical carbon dioxide modified with 5% methanol. At 250 atm and using carbon dioxide modified with 5% methanol, the recoveries of Cd2+, Pb2+, and Hg2+ ions from spiked sand samples were 95% with lithium bis(trifluoroethyl)dithiocarbamate (LiFDDC) as the chelating agent; they ranged from 83–97% with diethylammonium diethyldithiocarbamate and from 87–97% with sodium di-ethyldithiocarbamate as chelating agents, and from 68–96% with trifluoracetylacetone, hexafluoroacetylacetone, and thenoylfluoroacetone as chelating agents. Ammonium pyrrolidinedithiocarbamate was not effective in the chelation SFE of Cd2+, Pb2+, and Hg2+ ions from either spiked sand or spiked filter paper samples under the extraction conditions used. Supercritical carbon dioxide alone gave consistently lower analyte recoveries than supercritical carbon dioxide modified with 5% methanol. The results suggest that the solubility of the metal chelate in the supercritical fluid plays a more important role than the solubility of the chelating agent in the supercritical fluid, as long as sufficient chelating agent is present in the fluid phase. Fluorination of the chelating agent, as in the case of LiFDDC, increases the solubility of the metal chelate, and subsequently enhances the extraction efficiency for the metal ions. 相似文献
5.
Richard Young Viorica Lopez-Avila Werner F. Beckert 《Journal of separation science》1996,19(5):247-256
This paper describes the extraction of 20 organochlorine pesticides (OCPs) from water samples using solid-phase microextraction (SPME). Three fused-silica fibers coated or bonded with polydimethylsiloxane (PDMS) of different film thicknesses (20-, 30-, and 100-μm) were evaluated. The extraction time, the effects of stirring and addition of NaCl to the aqueous sample, the linear range and the precision of this technique, and the effect of carryover were examined for 20 analytes and are presented here. A comparison with results using conventional liquid-liquid extraction demonstrate that the SPME technique is well suited as a fast screening technique for OCPs in water samples. 相似文献
6.
Lesaw Bernard Lahuta Joanna Szabliska-Piernik Katarzyna Gowacka Karolina Staanowska Viorica Railean-Plugaru Marcin Horbowicz Pawe Pomastowski Bogusaw Buszewski 《Molecules (Basel, Switzerland)》2022,27(7)
Changes in the metabolome of germinating seeds and seedlings caused by metal nanoparticles are poorly understood. In the present study, the effects of bio-synthesized silver nanoparticles ((Bio)Ag NPs) on grains germination, early seedlings development, and metabolic profiles of roots, coleoptile, and endosperm of wheat were analyzed. Grains germinated well in (Bio)Ag NPs suspensions at the concentration in the range 10–40 mg/L. However, the growth of coleoptile was inhibited by 25%, regardless of (Bio)Ag NPs concentration tested, whereas the growth of roots gradually slowed down along with the increasing concentration of (Bio)Ag NPs. The deleterious effect of Ag NPs on roots was manifested by their shortening, thickening, browning of roots tips, epidermal cell death, progression from apical meristem up to root hairs zone, and the inhibition of root hair development. (Bio)Ag NPs stimulated ROS production in roots and affected the metabolic profiles of all tissues. Roots accumulated sucrose, maltose, 1-kestose, phosphoric acid, and some amino acids (i.e., proline, aspartate/asparagine, hydroxyproline, and branched-chain amino acids). In coleoptile and endosperm, contrary to roots, the concentration of most metabolites decreased. Moreover, coleoptile accumulated galactose. Changes in the concentration of polar metabolites in seedlings revealed the affection of primary metabolism, disturbances in the mobilization of storage materials, and a translocation of sugars and amino acids from the endosperm to growing seedlings. 相似文献
7.
Budrugeac P. Trandafir Viorica Albu Madalina Georgiana 《Journal of Thermal Analysis and Calorimetry》2003,72(2):581-585
The methods of the thermal analysis (TG, DTG and DTA) were used in order to investigate the effect of the hydration degree
on the thermal behaviour of some collageneous matrices. It was pointed out that the degradation of hydrated collagen in the
temperature range 20-400°C occurs through two successive processes accompanied by mass losses. The first process, consisting
in the collagen dehydration, is endothermic and takes place in the temperature range ≈25 - ≈125°C. The second process is exothermic
and consists in the decomposition and/or thermo-oxidation of dry collagen. The thermal parameters of both processes depend
on the hydration degree of collagen. The observed dependencies show that the hydrothermal and thermo-oxidative stability of
collagen are strongly correlated with its water content.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Werner Damm Carsten Ihlemann Viorica Sofronie-Stokkermans 《Mathematics in Computer Science》2011,5(4):469-497
This paper identifies an industrially relevant class of linear hybrid automata (LHA) called reasonable LHA for which parametric verification of convex safety properties with exhaustive entry states can be verified in polynomial
time and time-bounded reachability can be decided in nondeterministic polynomial time for non-parametric verification and
in exponential time for parametric verification. Properties with exhaustive entry states are restricted to runs originating
in a (specified) inner envelope of some mode-invariant. Deciding whether an LHA is reasonable is shown to be decidable in
polynomial time. 相似文献
9.
Monica R. Nemtanu Mirela Brasoveanu Viorica Meltzer Elena Pincu C. Oproiu 《Journal of Thermal Analysis and Calorimetry》2009,97(1):309-313
The purpose of the present work deals with the evaluation of the electron beam irradiation effects on some natural products
based on thermal analysis. Some natural products with therapeutic contributions (artichoke, sea buckthorn, common sage, stonebreaker
and cloves) were irradiated with doses up to 9 kGy using accelerated electron beam. The thermal profiles lead to identify
three phenomena: dehydration — volatilization, irreversible degradation — molecular reorganization and residue decomposition.
The radio-induced degradations determine slight shifts of the temperatures where these phenomena occur. The energetic value
of the studied products is affected by e-beam treatment depending on irradiation dose. 相似文献
10.
Viorica Mariela Ungureanu 《Journal of Mathematical Analysis and Applications》2008,343(1):446-463
The aim of this paper is to give a deterministic characterization of the uniform observability property of linear differential equations with multiplicative white noise in infinite dimensions. We also investigate the properties of a class of perturbed evolution operators and we used these properties to give a new representation of the covariance operators associated to the mild solutions of the investigated stochastic differential equations. The obtained results play an important role in obtaining necessary and sufficient conditions for the stochastic uniform observability property. 相似文献