Apparent retention volume variation with flow rate change in high performance liquid chromatography

Recent studies have demonstrated noticeable flow rate dependency of the chromatographic zone retention volume with respect to migration within the empty capillary. This appears to be the result of superposition of asymmetric lateral diffusion and of the laminar flow profile. Although these effects have been studied on empty capillaries, in the presence of the packed column, the retention shift may be insignificant relative to the adsorption-based retention of the analytes. In the case of fast and ultrafast HPLC with short capillary columns, the effect of extra-column caused variation in the analyte retention may constitute an increase of up to 120 % of the overall retardation. Small columns have very small column void volume, e.g. 1.0 x 50 mm with a column void volume of 24 μl, where the extra column volume within the connecting capillary can be as great as 185 μl. This great difference in volume, especially considering that some systems contain even longer connecting tubing for 2 dimensional HPLC or LC-MS systems, can demonstrate a significant shift in the overall retardation and may cause identification and quantitation problems. Experiments were done with common mobile phase solvents and readily available peek tubing at different variation of length and inner diameter. The origin of the phenomena is discussed, as well as the main influencing parameters such as capillary material, internal diameter, type and composition of the mobile phase. This research illustrates the importance of extra column volume on the overall separation in HPLC. The degree of band broadening and the apparent increase in retention volume is driven by the laminar flow profile and concomitant diffusion between the layers within the connective tubing of the HPLC system. The process of molecular diffusion alone has been shown to have negligible impact on this effect and is a positive outcome for systems requiring “parking” within sample loops such as in LC x LC systems. However, the deformation of sample plugs due to laminar flow effects were greatest at higher flow rates and in narrower tubing, which could have a significant impact on fast LC technologies such as UHPLC, short and narrow columns, and systems with unavoidable additional tubing lengths. This effect should be considered during method development and transfers between HPLC systems with variable extra column tubing dimensions and especially when utilizing micro columns with non-porous particles or in cases of minimally retentive analytes

A comparative analysis of the ethos-based statements made by John Kennedy and Richard Nixon in their 1960 presidential campaign speeches

Call number: LD2668 .T4 1969 B78Master of Scienc

Asymmetrien eines Ethernet-Systems und deren Auswirkungen auf die Störaussendung im automobilen Umfeld

Seit Jahren ist ein Zuwachs von elektronischen Komponenten im Fahrzeug zu beobachten. Der Wunsch nach mehr Komfort und Sicherheit trägt hier maßgeblich dazu bei. Um den Anforderungen gerecht zu werden, sind schnelle Übertragungssysteme im Fahrzeug erforderlich, die die großen Datenmengen verteilen und verarbeiten können. Ein solches System ist zum Beispiel Ethernet, mit dem periphere Komponenten mit hohen Datenraten vernetzt werden können. Eine spezielle Variante für den automobilen Einsatz stellt dabei das OABR-Ethernet (Open-Alliance-BroadR-Reach) dar. Dieses Kommunikationssystem nutzt eine bidirektionale Übertragungstechnik um 100MBit/s über eine ungeschirmte Zweidrahtleitung (UTP) zu übertragen. Eine weitere Besonderheit ist die Begrenzung des Nutzsignalspektrums durch einen Tiefpassfilter auf ca. 70MHz. Dadurch wird das Risiko einer Störung im UKW-Bereich minimiert. Der Einsatz dieses schnellen Übertragungssystems im Fahrzeug stellt jedoch eine große Herausforderung an die Elektromagnetische-Verträglichkeit (EMV) dar. Bereits kleine Asymmetrien im Übertragungspfad führen dazu, dass ein Teil des Nutzsignals (Gegentaktsignal) durch Modenkonversion in ein Störsignal (Gleichtaktstörung) umgewandelt wird - nachfolgend Modenkonversion genannt. Diese Gleichtaktstörungen können über die UTP-Leitung abstrahlen und zu Grenzwertüberschreitungen bei Störaussendungsmessungen führen. Jede Komponente im Übertragungspfad trägt maßgeblich zur Modenkonversion und somit zur Störaussendung bei. Diese Arbeit soll eine Übersicht über die Modenkonversion der einzelnen Elemente der physikalischen OABR-Schnittstelle geben. Diese Elemente sind im Einzelnen der Tiefpassfilter (LPF), die Common-Mode-Choke (CMC), die differentiellen Mikrostreifenleitungen (DML) sowie die Platinen- und In-Line-Stecker

Location-Based Protocol for the Pairwise Authentication in the Networks without Infrastructure

In this paper, we consider security issues arising in the development of the wireless networks without infrastructure, with the rapidly changing composition of the elements of such a network The LEAP Initial Protection (LEAP-IP) protocol proposed, which closes the vulnerability of the LEAP at the network initialization stage. Advanced LEAP-IP protocol allows to resist attacks on the radio channel, physical attacks on the device, and is energy efficient, that is especially important for devices with a limited power resource. Also, a classification of self-organizing networks and some variants of using the proposed pairwise authentication protocol is presented

New Governance for Rural America: Creating Intergovernmental Partnerships

Throughout the 1990s public demand for a fundamental shift in the relationship between government and its citizens has intensified. In response, a new governance model has emerged, emphasizing decreased federal control in favor of intergovernmental collaboration and increased involvement of state, local, and private agencies. As the authors of this volume show, one of the best examples of new governance can be found in the National and State Rural Development Councils (NRDC and SRDC), created in 1990 as the result of President Bush\u27s Rural Development Initiative and now called the Rural Development Partnership. This effort was part of a move within policymaking circles to redefine a rural America that was no longer synonymous with family farming and that required innovative new solutions for economic revival. By 1994 twenty-nine states had created and ten other states were in the process of forming such councils. In this first detailed analysis of the NRDC and SRDCs, the authors examine the successes and failures of the original eight councils in Kansas, Maine, Mississippi, Oregon, South Carolina, South Dakota, Texas, and Washington; as well as eight other councils subsequently created in Iowa, New Mexico, North Carolina, Vermont, New York, North Dakota, Utah, and Wyoming. Combining empirical analysis with current theories about networks and inter-organizational relations, this volume should appeal to academics and practitioners interested in rural development policy, public administration, public policy and management, and intergovernmental relations. Description Beryl A. Radin is professor of Public Administration and Policy in the Graduate School of Public Affairs at Rockefeller College of the State University of New York at Albany. This Kansas Open Books title is funded by a grant from the National Endowment for the Humanities and the Andrew W. Mellon Foundation Humanities Open Book Program.https://digitalcommons.pittstate.edu/kansas_open_books/1051/thumbnail.jp

Les ressources patrimoniales

Buntz Pierre. Les ressources patrimoniales. In: La Gazette des archives, n°168, 1995. Archives municipales et patrimoine industriel (actes du colloque de la Section des archivistes municipaux de l’AAF, Elbeuf, 25-27 mai 1994) pp. 106-109

Isolement et mise en evidence du pouvoir pathogene de Mycoplasma gallisepticum chez l'oie (Anser anser)

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Hand digitalization errors in transient analysis

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