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排序方式: 共有846条查询结果,搜索用时 0 毫秒
91.
92.
93.
Ingrid Fogy Erich R. Schmid und Josef F. K. Huber 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1980,170(3):194-199
Zusammenfassung Carbamatpesticide können auch in sehr komplex zusammengesetzten Obst- und Gemüsearten mit Hilfe der mehrdimensionalen Hochdruckflüssigkeitschromatographie im ppm-Bereich nachgewiesen werden. Dabei wird eine Fraktion des Effluents der ersten Säule, die das von Matrixbestandteilen nur unvollständig getrennte Pesticid enthält, mittels eines Schalthahns auf eine zweite Säule mit einer anderen stationären Phase gebracht, wo die Trennung vervollständigt wird. Die erhöhte Auflösung im Zweisäulen Betrieb wird durch die unterschiedlichen Selektivitätskoeffizienten von Wirkstoff und störenden Pflanzenbestandteilen in den beiden Phasensystemen bewirkt. Daneben kann man bei geeigneter Wahl der Fraktionsgrenzen eine relative Anreicherung des Carbamateserreichen. Da bei den verwendeten Phasensystemen die meisten Pflanzenbestandteile relativ schnell eluiert werden, gelingt besonders bei Carbamaten mit hohem Kapazitätskoeffizienten eine eindeutige Identifizierung und Quantifizierung manchmal schon mit der ersten chromatographischen Säule allein. Wegen der hohen Trennkapazität der mehrdimensionalen Hochdruckflüssigkeitschromatographie besteht die Probenvorbereitung nur aus einer Extraktion des Pflanzenmaterials mit Dichlormethan. Nach Ersatz des Extraktionsmittels durch die mobile Phase kann die Lösung direkt in den Flüssigkeitschromatographen injiziert werden.
Determination of carbamate pesticides in fruits and vegetables by multi-dimensional high pressure liquid chromatography
Summary Carbamate pesticides can be determined at the ppm level even in very complex extracts of different kinds of fruits and vegetables by means of multidimensional high pressure liquid chromatography. The effluent fraction of the first column containing the pesticide insufficiently separated from matrix compounds is transferred by column-switching to a second column with another stationary phase, where the separation is completed. The improved resolution in the two-column mode is caused by the different selectivity coefficients of carbamate and plant components for the two phase systems used. Furthermore, a relative enrichment of the carbamate can be achieved by a suitable choice of size and position of the transferred fraction. Carbamates with a high capacity factor can be determined on a single chromatographic column in general, since most plant constituents are eluted early on this type of column.Due to the high separating power of multidimensional high pressure liquid chromatography the sample pretreatment consists only of an extraction of the plant material with dichloromethane. After replacing the extraction solvent by the mobile phase the sample can be injected directly into the liquid chromatograph.相似文献
94.
Bonded neodymium-iron-boron (NdFeB) permanent magnets in a paired configuration were successfully used to control mass transport in redox-based, magnetohydrodynamics (MHD). Control of fluid flow based on magnetic fields has potential for use in portable lab-on-a-chip (LOAC) and analytical devices. Bonded magnets, composed of magnetic powder and organic binder materials, are less expensive and easier to fabricate and pattern than electromagnets and sintered permanent magnets, which have been previously used in MHD studies on electrochemical systems. The ability to pattern bonded magnets near and around the electrodes is expected to allow for better control over the magnetic field distribution and solution flow. Current was generated at an 800-microm-radius platinum disk electrode in a solution of 0.06 M nitrobenzene and 0.5 M tetra-n-butylammonium hexafluorophosphate in acetonitrile. Increases in limiting current in the presence of the magnetic field, which indicate enhancement in mass transport, for sintered (210+/-14%, N = 4, where B(r) = 1.23 T and magnetic field strength is 0.55 T) and bonded (94+/-8%, N = 4, where B(r) = 0.41 T and magnetic field strength is 0.20 T) magnets, were similar to those obtained using an electromagnet with the same magnetic flux densities. The magnetic field strength and not the magnet type is important in controlling fluid flow, which is encouraging for integration of bonded permanent magnets into LOAC devices. 相似文献
95.
96.
Repetti Rena L.; Matthews Karen A.; Waldron Ingrid 《Canadian Metallurgical Quarterly》1989,44(11):1394
This article reviews empirical evidence concerning the effects of paid employment on women's mental and physical health, with special attention to variations in the effects of employment depending on the characteristics of women and their jobs. We highlight methodological issues and focus primarily on studies with longitudinal data for representative samples of women. We conclude that women's employment does not have a negative effect on their health, on the average. Indeed, employment appears to improve the health of unmarried women and married women who have positive attitudes toward employment. Possible mediators linking employment to health outcomes are discussed. Current evidence suggests that increased social support from co-workers and supervisors may be one important mediator of the beneficial health effects of employment. Given the paucity of available longitudinal studies, we encourage additional prospective research examining the mental and physical health consequences of employment according to job characteristics, personal characteristics, and disease outcome. We also recommend research on several promising mediators of employment–health relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
97.
Aung K. Htoon Surjani Uthayakumaran Udayasika Piyasiri Ingrid A.M. Appelqvist Amparo López-Rubio Elliot P. Gilbert Roger J. Mulder 《Food chemistry》2010
The enzyme-resistant starch (ERS) content in processed high amylose and regular maize starches has been studied, with and without acid dextrinisation. The physicochemical and structural characteristics of the starches were analysed using a variety of techniques. The increase in ERS in high amylose maize starch with dextrinisation was related to the formation of a critical molecular weight fraction (MW ∼ 20,000) that could rearrange structurally. Further dextrinisation reduced the processed starch MW to below where it could still form ERS. Regular maize starch containing less than 30% amylose did not increase its resistance to amylase digestibility with acid dextrinisation, probably due to impairment of amylose rearrangement by the numerous branched amylopectin chains. The ERS, which is likely to form during the enzyme-digestion process, is a linear molecule with a maximum degree of polymerisation (DP) of 30, irrespective of the starch source, processing conditions applied or type and amount of acid used. 相似文献
98.
Silva AP Guimarães DE Mizurini DM Maia IC Ortiz-Costa S Sardinha FL do Carmo MG 《Lipids》2006,41(6):535-541
The purpose of this study was to evaluate the effects of four isoenergetic diets of differing fat composition on blood lipid
profile and adiposity in young rats. Diets containing different lipid sources—partially hydrogenated vegetable oil (PHVO),
palm oil (PO), canola oil (CO), and soy oil (SO)—were fed to lactating rats during the 21 days of lactation, and then fed
to young males following weaning until the 45th, day of life. In vivo lipogenesis rate (LR), lipid content (LC), relative level of FA, and the activity of lipoprotein lipase (LPL) enzyme were
measured in epididymal adipose tissue (EPI). Fasting blood lipoproteins and LC in the carcass were also appraised. Body weight
of PO and PHVO groups was significantly higher than CO and SO groups from day 14 of lactation to day 45, despite the lower
food intake in the PHVO group. PO and PHVO groups presented higher LR and LC in EPI than SO and CO groups. Carcass fat content
was significantly higher in PHVO and PO groups than in CO and SO groups. The LPL activity in EPI was unaffected by dietary
lipids. PHVO group had increased total cholesterol and TAG concentrations in comparison with the PO group, and significantly
lower HDL level compared with the other groups. These results show that the kind of FA in the dietary lipid offered early
in life can affect lipid metabolism and adiposity. 相似文献
99.
Ingrid Einsiedler 《电子与电脑》2009,(4):37-40
对于需要零故障和误差的自动充填和包装生产线而言,先进的图像处理系统正成为越来越不可或缺的部分。系统中使用的嵌入式计算机技术需要在恶劣环境中提供最佳的价格、高可靠性的实时性能。为满足这些需求, 相似文献
100.
Jan Van Ooteghem Bart Lannoo Koen Casier Sofie Verbrugge Emmeric Tanghe Wout Joseph Luc Martens Didier Colle Mario Pickavet Ingrid Moerman Piet Demeester 《Wireless Personal Communications》2009,49(3):391-414
Municipalities can form a driving force behind the deployment of new telecom infrastructure. While a telecom operator focuses
on direct (financial) profits, a municipality is mainly interested in the social benefits for its inhabitants. In this paper,
we evaluate a wireless municipality network from both a technical and an economic point of view. WiFi and WiMAX are considered
as the most suited technologies for this purpose. A detailed techno-economic study has been performed including forecasting
of the user adoption, dimensioning of the wireless network and modelling the related costs and revenues. The trade-off between
installing a high number of relatively cheap WiFi access points, and a smaller number of more expensive WiMAX base stations
for delivering full coverage is investigated in several scenarios.
相似文献
Piet DemeesterEmail: |