bluuebunny/crossref_metadata_2025 huggingface dataset:
Schichtcharakterisierung nitrocarburierter Stähle
Authors: Pohl M. , Al‐Rubaie K. S. , Steinmeier F.
Published: May 2005

In dieser Arbeit wird eine systematische Charakterisierung von Diffusionsschichten vorgenommen. Verschiedene Nitrocarburierverfahren, nämlich Salzbad, Gas und Plasma, wurden auf unterschiedliche Substrate angewendet. Bei den Substraten handelt es sich um die Stähle St 52‐3, Ck 45, 42 CrMo 4, 30 CrNiMo 8 und X 20 Cr 13. Die Schichtdicken und Porositäten wurden mit dem Lichtmikroskop bestimmt. Die Bestandteile der Verbindungsschicht wurden mittels der Röntgenfeinstrukturanalyse (RFA) und die Oberflächen‐Kenngrößen mit Hilfe des Tastschnittverfahrens ermittelt. Die Oberflächenhärten und die Härteverläufe wurden nach dem Vickers‐Verfahren untersucht.
Thermocyclic Behavior of Differently Stabilized and structured EB‐PVD thermal barrier coatings
Authors: Schulz U. , Fritscher K. , Leyens C. , Peters M. , Kaysser W. A.
Published: May 2005

The electron‐beam physical vapor deposition (EB‐PVD) process provides distinctive coatings of a unique columnar microstructure for gas turbine components. Main advantage of this structure is superior tolerance against straining, erosion and thermoshock, thus giving it a major edge in lifetime. This paper outlines the interaction between chemical composition and microstructural evolution EB‐PVD zirconia‐based thermal barrier coatings (TBCs) and their respective lifetimes in cyclic burner rig and furnace tests. Customizing TBC microstructure by adjusting EB‐PVD processing parameters is emphasized. A structural zone diagram for PVD is modified by interconnecting the influence of substrate rotation with microstructural evolutions. Finally, some basic aspects of single source and dual source evaporation are compared.
Lokales kumuliertes Schadensmaß für Komposite ‐ Rißspitzen ohne Singularität
Authors: Will P. , Helbig S.
Published: May 2005

Basierend auf dem begriff der Ausfallratefunktion wird der Vorschlag für ein lokales, kumuliertes Schadensmaß abgeleitet, das es ermöglicht das Versagensverhalten von Kompositen im inhomogenen spannungsfeld zu modellieren. Das Schadensmaß berücksichtigt die Akkumulation innerer, stochastischer schäden und eine damit verbundene Lastumverteilung auf ungeschädigte, tragende Volumenelemente. Als ein Anwendungsfall wird das Versagensverhalten von Biegebalken untersucht. Zum anderen wird nachgewiesen, daß lokale Schädigungen im Bereich der Rißpitze zum Verschwinden singulärer Spannungsfelder an der Rißfront führen.
Reibmodelle für elastomere und thermoplastische Werkstoffe und ihre Implementierung in Finite‐Elemente‐Codes
Authors: Hauk S. , Freitag E. , Hornberger K.
Published: May 2005

Bei der Entwicklung von dynamischen Dichtungen ist neben der Erfüllung der Dichtfunktion die Minimierung von Reibungsverlusten zu berücksichtigen. Moderne berechnungs‐ und simulationsunterstüzte Dichtungsentwicklungen müssen deshalb eine exakte Modellierung des Reibverhaltens integrieren. Im Fall der Polymerreibung zeigt der Reibkoeffizient signifikante Abhägigkeiten von Kontaktnormalspannung, relativer Gleitgeschwindigkeit und Temperatur. Diese Können mit dem klassischen Coulomb‐Reibmodell nicht beschrieben werden. Weiterführende Reibmodelle sind bisher noch nicht in kommerziellen FE‐Codes erhältlich, so daß deren Formulierung und Implementierung durch den Benutzer erfolgen muß.

Im vorliegenden Beitrag werden Berechnungsergebnisse vorgestellt, in denen das polymere Reibverhalten mit Hilfe geeigneter Modelle abgebildet und mit experimentellen Resultaten verglichen wird. Ferner werden Berechnungen der Kontaktflächenbildung zwischen Polymerprobe und Gegenkörper mit analytisch (Hertz Theorie) und experimentell ermittelten Kontaktflächen verglichen. Hierbei wird der Einfluß verschiedener Diskretisierungen gezeigt.
Messung elastischer Wellen in Stahl‐ und Gesteinsstäben mit Hilfe des magnetoelastischen Effektes
Authors: Hecker R. , Schulz R. K.
Published: May 2005

An Stahl‐ und Eisenerzstäben werden die durch einen Stoß ausgelösten elastischen Dehnwellen mit Hilfe eines Sensors gemessen, der den magnetoelastischen Effekt ausnutzt. Detektiert wird dabei die Änderung des magnetischern Flusses. Die theoretische Beschreibung der Ausbreitung elastischer Längswellen in Stäben erfolgt mit Hilfe der eindimensionalen Dehnwellengleichung. Die Übereinstimmung mit der Theorie wird exemplarisch durch Untersuchungen an Stahlstäben mittels Dehnungsmeßstreifen verifiziert. Danach werden die Signale von drei Eisenerzstäben (Magnetit, Hämatit, Siderit) aufgenommen. Bei den Gesteinen Magnetit und Hämatit lassen sich mit dem magnetoelastischen Aufnehmer Induktionsspannungen messen, während beim Siderit keine Signale aufgezeichnet werden konnten. Das bedeutet, daß für die Änderung des magnetischen Flusses nicht der Eisengehalt, sondern die Art der äußeren magnetischen Erscheinungsform der Proben entscheidend ist.

Der magnetoelastische Effekt bietet somit die Möglichkeit die durch eine Stoßbelastung in ferro‐ bzw. ferrimagnetischen Materialien ausgelösten mechanischen Wellen berührungslos mit Hilfe eines magnetoelastischen Sensors zu erfassen.
Zum Einfluß von Si und P auf das Verzinkungsverhalten Von Baustählen
Authors: Katzung W. , Rittig R.
Published: May 2005

Es wurde das Verzinkungsverhalten von 40 aktuellen Baustählen in Abhängigkeit vom komplexen Einfluß des Si‐/P‐Gehaltes bei den in der Feuerverzinkungsindustrie üblichen Bedingungen (440/450/460 °C, 5/10/15 min Tauchdauer) untersucht. Eine spürbare Wirkung von P auf das Schichtdickenwachstum von Stählen mit 0,01 bis 0,40 % Si beginnt bei > 0,020 % P. Der Einfluß von P ist um so größer je kleiner der Si‐Gehalt der Stählen und je niedriger die Temperatur der Schmelze ist. Bei Stählen mit ≤ 0,12 % Si verschiebt ein erhöhter P‐Gehalt die Schichtdickenmaxima in dem Temperaturbereich von 440 bis 450 °C, wie das sonst für Stähle > 0,12 % bis 0,28 % Si mit < 0,020 % P typisch ist. Zinküberzüge von Stählen mit kritischem P‐/Si‐Gehalt (0 bis 0,20 % Si/> 0,020 % P) sind in der Regel instabiler. Bei erhöhter Tauchdauer und o. g. Temperatur kann es zu einem Abschwimmen der ξ‐Phase in die Zinkschmelze kommen. Auch bei Sandelin‐Stählen im kritischsten Si‐Bereich (0,07 bis 0,10 %) mit < 0,020 % P konnte das bei 15 min Tauchdauer festgestellt werden. Es ist möglich, die Schichtdicke der Zinküberzüge durch Zulegieren kleiner Al‐Gehalte zur Zinkschmelze (< 0,03 %) zu reduzieren. Die Ursache dieses Effektes von Al unterhalb der Konzentration, die für die bekannte Hemmwirkung durch Ausbildung einer dünnen Fe2Al5 ‐bzw. Al‐haltigen δ11‐Schicht auf der Stahloberfläche erforderlich ist, wird auf die Instabilität der ξ‐Phase, die anteilig in die Zinkschmelze abschwimmt, Zurückgeführt.
PACVD‐Beschichtung von Druckgußwerkzeugen unter ökonomischen und ökologischen Gesichtspunkten
Authors: Pfohl C. , Gebauer‐Teichmann A. , Rie K.‐T.
Published: May 2005

Der heutige Stand der Technik in Aluminiumdruckguß erfordert den Einsatz von Formtrennmitteln. Zu deren Nebenwirkungen gehört aber eine Verschlechterung der Oberflächenqualität des Gußteils. Formtrennmittel beeinträchtigen die Arbeitsplatzqualität und sind unter ökologischen Gesichtspunkten als bedenklich zu betrachten. Um den Einsatz von Trennmitteln zu vermeiden und gleichzeitig die Standzeit der Druckgußwerkzeuge zu erhöhen, wurden nitridische, karbidische und boridische Schichten auf Titanbasis mittels DC‐Plus‐PACVD abgeschieden und im Hinblick auf ihren Einsatz im Aluminiumdruckguß optimiert. Durch die Beschichtung konnte bei gleichzeitiger Steigerung der Qualität der abgegossenen Teile die notwendige Trennmittelmenge um 97% reduziert werden. Die Standzeit der beschichteten Druckgußkerne im Vergleich zu unbeschichteten erhöhte sich durch die Beschichtung um über das 300‐fache.
On the sintering with rigid inclusions
Authors: Boccaccini A. R.
Published: May 2005

The sintering of porous matrices containing rigid, i.e. non‐densifying, inclusions is discussed on the basis of the composite sphere model of Scherer. Recognizing that internal stresses are generated by the presence of the non‐densifying inclusions, a new equation for the densification rate of the composite is proposed. It takes into account three contributions: (i) the free densification strain rate, which is independent of the stresses present, (ii) the strain rate due to the microscopic effect of the stresses on the sintering mechanism and (iii) the macroscopic deformation strain rate induced by the stresses. This result indicates that the presence of rigid inclusions may generate higher internal stresses in the densify ing compact than those calculated by the original Scherer's approach.
Herstellung Keramischer Schichten auf Leichtmetallen mittels plasmachemischer Verfahren in Elektrolyten
Authors: Kurze P.
Published: May 2005

Magnesiumwerkstoffe werden immer mehr in der Industrie insbesondere in der Automobilindustrie eingesetzt.

Die spezifischen Eigenschaften dieses Materials werden beschrieben. Ein neues Verfahren zur Oberflächenbeschichtung ‐Magoxid‐Coat‐zur Verbesserung des Korrosions‐ und Verschleißschutzes der Magnesiumwerkstoffe wird vorgestellt.

Beispiele für Anwendungen werden gegeben.
Schallemissionsmessungen beim Rißfortschritt in Stahl unter statischer Belastung
Authors: Lysak M. W. , Je Andrejkiw O. , Skalskyj W. R.
Published: May 2005

Zur Bewertung des Rißfortschritts in Abhängigkeit des Spannungsintensitätsfaktors KI in Dreipunktbiegeproben aus dem hochfesten Stahl 38 ChN3MFA durch Parameter der Schallemission (SE) wurde ein geeignetes Verfahren entwickelt und erprobt. Die Schallemissionsdaten gestatten die Erfassung von Rißstart und Rißfortschritt. Mit zunehmender Annäherung von KI an KIC wurde eine rasche Zunahme an neugebildeter Rißfläche beobachtet.
Anwendung der Fehlstellentheorie nach Weibull zur Berechnung des statistischen Größeneinflusses bei Dauerschwingbeanspruchung
Authors: Friederich H. , Kaiser B. , Kloos K. H.
Published: May 2005

An Proben unterschiedlicher Durchmesser aus vergütetem Stahl 42 CrMo 4 wurden bei Raumtemperatur einstufige Versuche bei Axial‐ und Umlaufbiegebeanspruchung durchgeführt. Die experimentell ermittelten dauerfest ertragbaren Nennspannungsamplituden wurden berechneten Werten gegenübergestellt.

Hiermit konnte gezeigt werden, daß das Fehlstellenmodell nach Weibull in der von Heckel angewandten Form bei gleicher Datenbasis anderen Ansätzen hinsichtlich der Genauigkeit der Schwingfestigkeitsberechnung überlegen ist.
Anwendung des Fehlstellenmodells auf die Dauerfestigkeit des Stahls 100Cr6 im bainitischen Zustand
Authors: Bomas H. , Linkewitz T. , Mayr P.
Published: May 2005

As Proben des hochfesten Stahls 100Cr6 im bainitischen Zustand wird der Einfluß von Kerben und Belastungsart auf die Dauerfestigkeit aufgezeigt. Das Verhalten der Proben, die so geschliffen waren, daß an der Oberfläche Druckeigenspannungen vorlagen, kann mit einer räumlich darstellbaren Schwingfestigkeitshypothese und dem Fehlstellenmodell, angewandt auf Volumenfehler, quantitativ beschrieben werden. Hieraus ergibt sich die Möglichkeit, für jede Nennspannungsamplitude örtliche Bruchwahrscheinlichkeiten und Gesamtbruchwahrscheinlichkeiten sowie Anrißort und Dauerfestigkeit vorherzusagen. An ungekerbten Zug‐Druck‐Proben wurde der Zusammenhang zwischen der Überlebenswahrscheinlichkeit und der Größenverteilung der bruchauslösenden Einschlüsse nachgewiesen.
Corrosion of Zinc in acetic acid derivatives: Glycollic, mercaptoacetic and cyanoacetic acids and glycine
Authors: Abd El‐Rahman H. A. , Gad‐Allah A. G. , Tamous H.
Published: May 2005

The corrosion behaviour of zinc in glycollic, mercaptoacetic and cyanoacetic acids and glycine was studied by weight loss, pH‐monitoring and polarization measurements. The rate of corrosion was found to be a first order with respect to hydrogen ion activity and strongly dependent of the acid type. The abnormal behaviour in cyanoacetic acid at < 0.5 M was attributed to the hydrolysis of the acid during the corrosion and formation of malonic acid as confirmed by FT‐IR spectroscopy. Morphological investigation of the corroded surfaces showed localized corrosion in cyanoacetic and glycollic acids which increased as the acid concentration or corrosion time increased. The FT‐IR analysis indicated also the formation of zinc glycollate and zinc thioglycollate as the corrosion products of zinc in glycollic and mercaptoacetic acids, respectively (Scheme 1a+b).
Untersuchung der Verbindungseigenschaften an laserstrahlgefügten Brillengestellen
Authors: Dorn L. , Jafari S. , Hofmann F.
Published: May 2005

Bei der Fertigung von hochwertigen Brillengestellen aus nichtrostenden Stählen gewinnt der Einsatz der Laserstrahlfügeverfahren im Vergleich zu konventionellen Verfahren zunehmend an Bedeutung. Im Rahmen einer Studie sollte festgestellt werden, welches der beiden Verfahren Löten und Schweißen die in der Praxis gestellten Anforderungen an Brillengestelle besser erfüllt. Hierzu wurden Profile aus Cr‐Ni‐Stahl, wie sie in der Praxis wegen ihrer besonderen Langzeitstabilität gegenüber Korrosion eingesetzt werden, mittels Laserstrahl gefügt. Zur Charakterisierung der metallurgischen Eigenschaften der Fügeverbindungen wurden die Qualitätsmerkmale der Proben hinsichtlich mechanischer Eigenschaften (Härte, Festigkeit und Verformbarkeit) sowie die Gefügeausbildung untersucht. Im Hinblick auf die geforderte gute Verformbarkeit der Verbindungen konnte für die geschweißten Proben ein Vorteil gegenüber dem Laserstrahllöten nachgewiesen werden.
Plasmasensorik in gepulsten PACVD‐Plasmen
Authors: Klümper‐Westkamp H. , Mehner A. , Hoffmann F. , Mayr P.
Published: May 2005

Langmuirsonden werden seit langem als grundlegendes Plasmadiagnosesystem zur Bestimmung lokaler Plasmaparameter wie Elektronen‐ und Ionendichte, Elektronentemperatur oder Plasmapotential benutzt. Die Erfahrungen mit Langmuirsonden haben gezeigt, daß Modifikationen der Sondenoberfläche durch Verunreinigungen oder durch Beschichtung zu signifikanten Veränderungen im Sondensignal führen können [5 – 16].

Durch den Einsatz dieses Sensors sollen insbesondere jene Vorgänge, die zu einer lokalen oder generellen Verschlechterung der technologischen Schichteigenschaften führen, bereits in der Phase der Schichtentstehung erkannt und durch Variation der Prozeßparameter während der Schichtabscheidung vermieden werden. Eine solche sensorkontrollierte Prozeßsteuerung könnte den industriellen Einsatz der PACVD‐Technik auf eine breitere Basis stellen, da die gewünschten technologischen Schichteigenschaften bereits während des Prozesses über eine geeignete Prozeßführung beeinflußt werden können.
Entwicklungstrends in der Scheibenbremstechnologie für Schienenfahrzeuge
Authors: Zeuner T. , Ruppert H. , Engels A.
Published: May 2005

Developing trends in disc brake technology for rail application

The substitution of conventional ferrous materials by light‐alloy solutions gives the opportunity for significant reduction of the rotating masses in the bogie and by that a decrease of energy consumption. The potential of conventional Al‐cast‐alloys is not suitable to solve this. Castable MMC‐materials are a high‐promising alternative. Under economic pressure MMC‐solutions need not to be only superior but also cost effective. And due to the low ductility of those particulate reinforced materials there is a need for new concepts.

Locally optimised disks consist of a ductile carrier [body] with wear resistant rubbing surfaces. This led to several prototype disk brakes manufactured by different casting processes.

This paper gives an overview about the state‐of the‐art and newly developed manufacturing routes and materials, metallic and non‐ metallic, for rail disk brake application.
The use of polar modifiers in microbore supercritical fluid chromatography combined with inductively coupled plasma spectrometry
Authors: Fujimoto Chuzo , Yoshida Hiroyuki , Jinno Kiyokatsu
Published: May 2005

An interface developed for detection of microbore supercritical fluid chromatographic (SFC) effluents with an inductively coupled plasma (ICP) spectrometer is described. The effect of modifiers on chromatographic peak intensity was investigated with respect to reproducibility, nebulizing gas flow rate, and viewing height. With 8.0 mol % methanol and 7.3 mol % acetonitrile in carbon dioxide, the interface allowed the total effluent from the microbore column to be introduced into the plasma without degrading the performance of the system. The applicability and usefulness of the SFC‐ICP system are demonstrated using standard mixtures.
Direct introduction of aqueous eluents for on–line coupled liquid chromatography–capillary gas chromatography
Authors: Cortes Hernan J. , Pfeiffer Curt D. , Jewett Gary L. , Richter Bruce E.
Published: May 2005

The on‐line introduction of relatively large volumes of reversed‐phase (aqueous) eluents into a capillary GC column without severe distortion of components eluting at temperatures close to the solvent boiling point is described. The technique, which utilizes an uncoated inlet (retention gap), is based on complete evaporation of the solvent prior to reaching the stationary phase and introduction of components with a dispersion equivalent to that given by a micro‐LC system. Studies of the evaporation within the retention gap, accomplished by introduction of a nonvolatile dye and visual examination of the resulting band patterns, indicated minimum retention gap lengths necessary to prevent liquid solvent from reaching the capillary GC column when aqueous eluents are used. The determination of N‐Serve' (2‐chloro‐6‐[trichloro methyl]pyridine) in corn extract is described.
Supercritical fluid chromatography–supersonic jet spectroscopy: I. Microcolumns and direct expansions
Authors: Simons John K. , Sin Chung Hang , Zabriskie Norman A. , Lee Milton L. , Goates Steven R. , Fields Steven M.
Published: May 2005

Direct supersonic expansions of the eluent from a supercritical fluid chromatograph have been investigated as a means of attaining high selectivity in laserinduced fluorescence detection of polycyclic aromatic hydrocarbons. The direct expansion method appears impractical for capillary SFC, but it works well for microbore, packed‐column supercritical fluid chromatography. Perylene and benzo[a]pyrene were selectively detected at limits of 0.5 ng and 40 ng, respectively, in standard mixtures and coal tar samples.
High‐speed gas chromatography using an on‐column thermal desorption modulator
Authors: Liu Zaiyou , Phillips John B.
Published: May 2005

A short, narrow‐bore (50 μm) column with an on‐column thermal desorp‐ tion modulator provides a technically simple and reliable method to generate high‐ speed gas chromatograms. A thermal desorption modulator prepared on the column but operated at a lower temperature functions as a sample introduction device. The modulator portion of the column extends outside of the oven and is at room temperature. A sample stream flows continuously into the modulator and through it into the column. Retained sample is released from the modulator by an electricaliy generated temperature pulse and carried into the column as a concentration pulse analogous to a sharp injecfion. Because the modulator is part of the column, no external injector is needed, and the volume of the concentration pulse is automatically appropriate for the column diameter. A series of chromatograms can be generated from a continuously flowing sample stream by applying a series of temperature pulses to the modulator. The narrow‐bore column is highly efficient and generates chromatograms with total retention times as short as 1 s. Chromatographic efficiency reaches the column's the oretical limit at very high carrier gas linear velocity. Measured terminal band lengths are shorter than the length of the modulator because the thermal gradient between modulator and column focuses bands as they enter the column. Band durations are less than the modulator thermal pulse duration because sample substances are released from the modulator stationary phase and carried onto the column during a small part of the temperature ramp.
New nitrophenyl‐ and nitromethoxyphenyl‐substituted methylpolysiloxane stationary phases for capillary column gas chromatography
Authors: Juvancz Zoltan , Pulsipher Michael A. , Schirmer Michelle M. , Johnson R. Scott , Markides Karin E. , Bradshaw Jerald S. , Lee Milton L.
Published: May 2005

Nitrophenyl‐, nitrophenylethyl‐, dinitrophenylethyl‐, and methoxynitrophen‐ ylethyl‐substituted polysiloxanes (25‐50% substitution) have been synthesized and evaluated as stationary phases in capillary column gas chromatography. Phases with 25% substitution and with ethylene spacers between the phenyl substituents and the polysiloxane backbone were found to provide high efficiencies, moderate thermal stabilities, and useful selectivities. Without flexible hydrocarbon spacers, the station‐ ary phases exhibited poor efficiencies. The 50% substituted phases generally provided narrower operational temperature ranges and lower efficiencies, and they were more difficult to immobilize by free radical crosslinking. Several methods of immobilization were evaluated, and a dynamic procedure with dicumylperoxide (DCP) was found to produce the best results for these nitrophenyl‐containing phases. The enhancements in polarity resulting from the resonances of the nitrophenyl substituent groups pro‐ vided unique selectivities for specific applications involving aromatic compounds. The dinitrophenyl‐containing phases showed, in addition, selectivity based on charge transfer complex formation.
Resolution of optical isomers of 2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucopyranosyl isothiocyanate (GITC)–derivatized DL‐amino acids by micellar electrokinetic chromatography
Authors: Nishi Hiroyuki , Fukuyama Tsukasa , Matsuo Masaaki
Published: May 2005

Resolution of isomers of 2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucopyranosyl isothiocyanate (GITC)–derivatized DL‐amino acids was accomplished using micellar electrokinetic chromatography with sodium dodecyl sulfate (SDS) solutions. These solutes were not separated by the usual capillary zone electrophoresis. Of 21 DL‐amino acids, optical resolution was recognized in 19 under the neutral and alkaline conditions; aspartic acid and glutamic acid have an additional carboxyl group. Simultaneous resolution of more than ten GITC derivatized DL‐amino acids was achieved within 40 min with the addition of 0.2 M SDS. The diastereomers of aromatic, heterocyclic, and basic DL‐amino acids were successfully separated owing to their effective solubilization into the SDS micelle, although a few peaks of the derivatives coeluted.
Analysis of cis‐platinum using a microcolumn with a β‐cyclodextrin stationary phase and electrochemical detection
Authors: Dolezel Petr , Kourilova Dana , Krejci Milos , Smolkova‐Keulemansova Eva
Published: May 2005

A simple method for determining chemotherapeutically active cis‐platinum using a β‐cyclodextrin stationary phase on a silica gel carrier (β‐CD‐sil) is described. Retention of CDDP is considerably influenced by the content of acetonitrile in the mobile phase. With an electrochemical detector in oxidation mode, the minimal detectable amount of CDDP was determined to be 1.6 · 10−11 mol, and the minimal detectable concentration in the sample was 5 ppm (5 m̈g/mL). The method was used to determine CDDP concentration in the samples of body fluid (ascites).
Preliminary examination of the photoionization detector for microbore column supercritical fluid chromatography
Authors: Onuska Francis I. , Terry Ken A.
Published: May 2005

A photoionization detector (PID) has been evaluated for its applications in supercritical fluid chromatography using microbore columns. The PID is a nondestructive detector which is sensitive to the concentration of the analyte. Thus, maximum sensitivity is obtained at low flow rates. The PID dynamic range in supercritical fluid chromatography is approximately 104, which is much smaller than in gas chromatography. Although the PID appears to complement the flame ionization detector (FID) in many respects, it should be considered of limited value in environmental trace analyses due to the large cell volume. The PID can be used with both conventional and microbore packed columns; however, the detector used in this study is not suitable in its present design for capillary SFC.
Preparation and separation properties of open tubular columns with immobilized Carbowax 20M for LC
Authors: Janák Karel , Horká Marie , Krejčí Miloš
Published: May 2005

Open tubular columns (3‐5 m × 23‐50 μm i.d.) were coated with Carbowax 20M (0.07‐0.2 μm film thickness) and immobilized with pluriisocyanates (Desmodur N or Desmodur L), a method which is simple, rapid, and reproducible. The concentration of cross‐linking agent and the preparation conditions were optimized with respect to stability and separation properties of the immobilized film under liquid chromatography (LC) conditions. Properties of columns in LC systems are strongly dependent on the degree of immobilization and slightly dependent on the type of Desmodur used as a cross‐linking agent. The degree of immobilization must exceed 90% for successful application in LC. Such columns displayed good long‐term stability, especially when immobilized with Desmodur L. Using water as the mobile phase, the LC system behaved as a reversed phase system. Capacity ratio and temperature strongly affected the separation efficiency.
Optimization of pH in the electrophoretic separation of 2‐, 3‐, and 4‐methylpyridines
Authors: Wren Stephen
Published: May 2005

The 2‐, 3‐ and 4‐substituted methylpyridines were used to investigate the theoretical and experimental relationships between pH and separation in free solution capillary electrophoresis. Separation was improved by the use of a cationic surfactant to suppress electroosmotic flow. The electrophoretic mobilities of the 3‐ and 4‐isomers were examined and found to be linearly dependant upon calculated charge.
Polymerization of formic acid on porous glassy carbon surface
Authors: Engel Tina M. , Olesik Susan V.
Published: May 2005

While using porous glassy carbon (PGC) as a stationary phase for supercritical fluid chromatography (SFC), irreversible modifications of the PGC surface were observed when using 3% formic acid in supercritical carbon dioxide mobile phase at mild operating conditions. Scanning electron microscopic and energy dispersive X‐ray spectroscopic analyses indicated the formation of a polymer coating on the PGC surface. The coating may be formed from a polymerization reaction of the formic acid modifier catalyzed by the presence of the carbon surface. Those using carbon‐based stationary phases should be aware of this reaction when using formic acid as a modifier for SFC.
Combined two‐dimensional GC/MS/matrix isolation FT‐IR with a versatile sample introduction system
Authors: Rodriguez Pedro A. , Eddy Cynthia L. , Marcott Curtis , Fey Monica L. , Anast John M.
Published: May 2005

A versatile sample introduction system or injector/trap (I/T), described in this paper, is a stand‐alone, computer‐controlled, cryogenic concentrator with provisions for solvent venting and inert sample transfer. The I/T is designed to provide a common interface between the column and a variety of sampling modules.

Modules to perform thermal desorption and pyrolysis, as well as modules for remote sampling (pre‐traps) have been developed. Large volumes of either gaseous or liquid samples can be introduced by means of pre‐traps packed with suitable substrates. Pretraps packed with Tenax TA allowed quantitative recovery of compounds as volatile as n‐decane (n‐C10) when contained in a 1‐mL volume of pentane. The introduction of a 1–mL sample makes it possible to reach a detection limit of ca. 100 ppt,

ppt, ppb, ppm refer to parts‐per‐trillion (1012), billion (109), and million (106), respectively.

with an FID, for compounds with boiling points ≥n‐C9.

The capability to do trace analyses with the I/T is enhanced by interfacing it to a twodimensional gas chromatograph (2D/GC) equipped with a mass‐selective detector (MSD) and a matrix isolation fourier transform infrared spectrometer (MI FT‐IR). The resulting instrumentation greatly facilitated the identification of organic compounds present at ppbconcentrations in perfume samples.
Preparation of reversed phase open tubular liquid chromatographic columns from borosilicate glass
Authors: Claire Robert L. St. , Dohmeier Daniel M. , Jorgenson James W.
Published: May 2005

The preparation of open tubular liquid chromatographic columns with small inner diameters (≤ 20 μm) from Pyrex 7740 borosilicate glass is described. The surface area of the inner wall of the capillary is increased by etching with a series of acidic and basic solutions. Dimethyloctadecylchlorosilane is then reacted with the column wall to create a bonded stationary phase layer. The resulting columns exhibit good retention and high efficiency. The effects of each step in the etching process are examined and the silanization reaction is optimized.
4‐(Methylsulfonyl)phenyl‐containing polysiloxane stationary phase for capillary column gas chromatography
Authors: Juvancz Zoltan , Schirmer Michelle M. , Johnson Deborah F. , Markides Karin E. , Bradshaw Jerald S. , Lee Milton L.
Published: May 2005

A new polar polysiloxane stationary phase for capillary column gas chromatography containing 4‐(methylsulfonyl)phenyl substitution was synthesized and compared to a cyanophenylpolysiloxane, OV‐225. The sulfonylphenylpolysiloxane phase was useful and stable over a wide temperature range from 70°C to 320°C, and it exhibited similar overall polarity to OV‐225. However, because of the specific chemical properties of the 4‐(methylsulfonyl)phenyl group, this phase demonstrated unique selectivities for certain classes of compounds including basic nitrogen heterocycles and polychlorinated biphenyls.
Polymeric coatings in packed fused silica micro‐LC columns
Authors: Ghijs Marleen , Sandra Pat
Published: May 2005

Different polymer‐coated stationary phases have been evaluated in micro‐LC: Nucleosil‐100‐5‐C1‐PMSC18 (C18‐substituted polymethylsiloxane, C1‐deactivated with trimethylsilylenolate) and Nucleosil‐100‐5‐C1‐PMSCN (cyanopropyl‐substituted polymethylsiloxane, C1‐deactivated) in the reversed phase mode and Nucleosil‐100‐5‐PEG (polyethylene glycol‐coated) in the normal phase mode.

Fused silica tubing of 320‐μm i.d. was slurry packed with suspensions optimized for each packing material. The micropacked columns were studied for efficiency and selectivity. The silanol activities of the polymer coated phases were compared to monomeric phases for the reversed phase mode and to silica for the normal phase mode.
Chemical analysis of bis(5‐amidino‐2‐benzimidazolyl) methane in the arthritic rat knee using microdialysis and microcolumn liquid chromatography
Authors: Claire Robert L. St. , Brouwer Kenneth R.
Published: May 2005

Microcolumn liquid chromatography and microdialysis were coupled together to study the distribution of an IV administered drug into the knee joint of a rat with acute arthritis. Dialysate from microdialysis probes located directly within the intraarticular region and in the surrounding muscle was delivered at a flow rate of 0.25 μL min−1 directly into a microcolumn LC system. A 0.5‐mm i.d. microcolumn and fluorescence detector were utilized. An in vitro model was developed to estimate the drug concentration in the dialysate. Differences in drug distribution between the intra and extraarticular knee regions were detected, and the potential utility of this technique in the pharmacokinetic evaluation of site‐specific drugs was demonstrated.
Examination of variables affecting the performance of isoelectric focusing in uncoated capillaries
Authors: Mazzeo Jeff R. , Krull Ira S.
Published: May 2005

The effects of different variables on protein separation by isoelectric focusing in uncoated capillaries were investigated. Four model proteins were used to study the effects. The variables included applied electric field, column length, % methyl cellulose, % tetramethylethylenediamine (TEMED), and buffer concentration. Methyl cellulose showed a bimodal effect on the separation performance in terms of migration time and peak width. It was determined that the optimal %TEMED and applied field depended strongly on each other. Furthermore, longer column lengths led to better resolution at constant field and % TEMED. Using a grid, the applied electric field and % TEMED were optimized concurrently at a fixed column length.
(S) ‐TroloxTM methyl ether, a powerful derivatizing reagent for the determination of the enantiomeric purity of chiral alcohols by GC and SFC with achiral columns
Authors: Walther Wiley , Vetter Walter , Netscher Thomas
Published: May 2005

The enantiomers of aliphatic alcohols are transformed by a new chiral reagent (S)‐Trolox methyl ether to their diastereomeric esters which are separated by capillary GC or SFC on achiral columns. The applicability of this reagent and its superiority to the hitherto known reagents are demonstrated by selected examples.
Temperature‐programmed microcolumn liquid chromatography/mass spectrometry
Authors: Yoo Jong Shin , Watson J. Throck , McGuffin Victoria L.
Published: May 2005

A temperature‐programmed microcolumn liquid chromatography/mass spectrometry (LC/MS) system has been developed as a practical alternative to conventional solvent‐programmed LC/MS. Good reproducibility of solute retention was achieved in a specially modified oven that permitted linear temperature programming between 40 and 100°C at rates of 0.1 to 0.5°C min−1. Through theoretical modelling studies performed under isocratic and isothermal conditions, the optimum separation under temperature‐programmed conditions was rapidly and accurately predicted. This method enabled the complete resolution of saturated and unsaturated fatty acids in a fish oil dietary supplement with identification from their characteristic fragmentation patterns under electron‐impact MS conditions. The mass spectra from the LC/MS system correlated very well with those from a standard reference library to facilitate spectral searching methods.
Optimization of the eluent delivery system for micro size‐exclusion chromatography
Authors: Alexandrov Maxim L. , Belenkii Boris G. , Gotlib Vladimir A. , Kever Jeno E.
Published: May 2005

The problems of microcolumn size‐exclusion chromatography and its instrumentation are considered. It is shown that the reproducibility of retention times of a micro‐gel chromatograph depends on the stability of eluent delivery by a syringe micropump. It is possible to increase this stability and to suppress the relaxation processes related to the changes in hydrodynamic column resistance and in the solvent temperature in the pump chamber.

In order to suppress instability when columns of 0.5‐mm inner diameters are used, the volume of the eluent delivery system should be as small as possible (Vp ⩽ 1 mL) and the system should be thermostatted at ΔT 〈P∞(α/β)δ where P ∞ is the pressure under conditions of constant pump pressure, α and β are the coefficients of thermal expansion and compressibility of the liquid, and δ is the permissible retention time error (ΔtR/tR).
Refractometric detector for a microcolumn high‐performance size‐exclusion and micro gel chromatograph
Authors: Alexandrov Maxim L. , Belenkii Boris G. , Gotlib Vladimir A. , Kever Jeno E.
Published: May 2005

It is shown that an interference‐polarizing refractometric detector makes it possible to use microcolumn size‐exclusion chromatography (MSEC) columns with inner diameters of 0.2 to 0.5 mm and ensures a detection limit (at a signal to noise ratio of 3) of 8 × 10−8 refractive index units.

Taking into account the above requirements, a micro‐gel chromatograph with a refractometric (interference‐polarizing) detector was developed. Teflon columns gave reproducibilities (the mean square deviation at the 95% confidence level) of retention times and signal amplitudes of 0.2% and 0.5%, respectively, which ensures reproducibilities of molecular weight determinations within about 2 to 4%. Examples of polymer and protein analyses carried out on this chromatograph are given. It is suggested that a micro‐gel chromatograph can be developed for fused‐silica capillary columns with inner diameters of 0.2 mm. This would permit analysis of approximately 10 pg of polymer.
Capillary GC analysis of biogenic amines, their precursors and catabolytes after fast derivatization with ethyl chloroformate
Authors: Hušek Petr
Published: May 2005

Six aromatic biogenic amines, three aromatic amino acid precursors, four aromatic hydroxycarboxylic acid catabolytes, and two aromatic glycols were analyzed by capillary GC after derivatization. Instantaneous derivatization was performed by reaction with ethyl chloroformate in a medium of aqueous acetonitrile containing ethanol and pyridine. After extraction of the derivatives into chloroform, the sample was ready for analysis.
Separation of C60 and C70 fullerenes on methoxyphenylpropyl bonded stationary phases in microcolumn liquid chromatography
Authors: Jinno Kiyokatsu , Saito Yoshihiro , Chen Yung‐Lin , Luehr Gary , Archer Jim , Fetzer John C. , Biggs Wilton R.
Published: May 2005

Chromatographic separation of C60 and C70 fullerenes was performed with phenylpropyl and three different methoxyphenylpropyl bonded phases in microcolumn liquid chromatography. The results indicate that the 3,4‐dimethoxyphenylpropyl phase possesses the best resolving power among the evaluated phases, producing a separation factor of 1.87 for C70 and C60 using n‐hexane as the mobile phase. This observation could be explained by examining the energy minimized conformations of the bonded phases and their associative interactions with the fullerene molecules.
Direct chiral resolution of amino acid derivatives by capillary electrophoresis
Authors: Okafo George N. , Camilleri Patrick
Published: May 2005

A mixture of sodium deoxycholate and β‐cyclodextrin has been used to resolve the enantiomers of the 1‐cyano‐2‐substituted‐benz[L]isoindole and dansyl derivatives of a variety of amino acids. The enantiomers of CBI‐histidine and glutamic acid were resolved with this system unlike the case of γ‐cyclodextrin in combination with SDS reported in the literature. Dansyl derivatives have been generated in situ to provide information about the migration behavior of dansylic acid, a major by‐product in the dansylation.
Fullerene‐linked particles as LC chromatographic media and modification of their electron donor/acceptor properties by secondary chemical reactions
Authors: Stalling David L. , Guo Congyuan , Kuo Kenneth C. , Saim Said
Published: May 2005

Fullerenes (C60 and C70) linked to small silica or polymer particles provide novel chromatographic stationary phases with electron donor/acceptor surface interactions that may parallel those of aromatic carbons. Separations of fullerenes and aromatic compounds frequently encountered as environmental contaminants were investigated using LC microcolumns containing either particles prepared from BrHC60 linked to amino‐silica (Spherisorb‐NH2, Phenomenex) or porous polymers containing ca. 12% fullerene by weight. The polystyrene divinylbenzene (PSDVB)‐C60/70H column had greater capacity (k') than the SiNHC60/70H column. Toluene and polycyclic aromatic hydrocarbons (PAHs), naphthalene, anthracene, pyrene, and perylene, were retained in the order of increasing ring number; nitro‐substituents increased retention; and chlorinated‐dibenzo‐p‐dioxins and ‐dibenzofurans were more strongly retained than their parent compounds. PCB congeners with no chlorine in the ortho, ortho'‐positions are co‐planar and are strongly retained; for these isomers, retention increased with higher chlorination. We demonstrate that surface‐linked fullerenes can also accommodate further chemical modification through the addition of 2‐(4‐nitrophenyl)ethyl or ‐NHCH2CH2NH2 moieties to yield altered electron donor/acceptor affinity. Separations appear to be derived primarily from aromatic electron induced dipole‐dipole or electron‐pair donor or acceptor interactions (charge transfer complexes). Except for the fullerenes, surface interactions with compounds are largely suppressed with methylene chloride as the mobile phase.
Band broadening during mobile phase change in unified chromatography (GC‐SFC)
Authors: Tong Daixin , Bartle Keith D.
Published: May 2005

Band broadening brought about by changing the mobile phase from the GC mode to the SFC mode in unified chromatography is discussed. Its origin is shown to result from several factors: the replaceable volume of the tubing and valves in front of and following the column; the volume, internal diameter, and film thickness of the open tubular column; the initial pressure of the supercritical mobile phase; and the column temperature. Improvements to restrict band broadening were achieved by optimizing the system and its operating conditions.
Polymeric hollow fibers for capillary electrophoresis
Authors: Liu Peter Z. , Malik Abdul , Kuchar Marvin C. J. , Vorkink William P. , Lee Milton L.
Published: May 2005

In this paper, polymeric hollow fibers prepared from polypropylene and polybutylene terephthalate were used as CE columns. Surface modifications with polyacrylamide greatly improved the performance of the capillaries. Separations of substituted pyridines, model proteins and standard ribonucleotides were demonstrated. The column efficiency for model proteins was over 200,000 theoretical plates. Comparisons of electroosmotic flow, UV absorption properties, heat dissipation, and diameter variation between fused silica capillaries and polymeric hollow fibers were made. The practical potential of small diameter polymeric hollow fibers as CE columns was evaluated.
Preparation and evaluation of an on‐line preconcentrator for capillary electrophoresis
Authors: Hoyt Arthur M. , Beale Stephen C. , Larmann John P. , Jorgenson James W.
Published: May 2005

The preparation and performance of an on‐line preconcentrator for capillary electrophoresis (CE) is described. Borosilicate glass microspheres were dry‐packed into the fused silica column terminus and sintered in place with a micro electric are developed for this application. Reversed‐phase LC packing material was slurry‐packed onto this frit, in lengths of 1‐3 mm. An additional frit of borosilicate beads behind the preconcentrator was used to fix the packed bed in place. The performance of the packed bed preconcentrator for the enhancement of UV and fluorescence detection limits was evaluated. Construction of the micro electric are device, the packing procedures, and practical applications are described.
Preparation of long packed capillary columns using carbon dioxide slurries
Authors: Malik Abdul , Li Wenbao , Lee Milton L.
Published: May 2005

A new, reproducible method is described for the preparation of highly efficient fused silica packed capillary columns using pressure programmed liquid or supercritical carbon dioxide to carry the packing material into the capillary. The method allows facile preparation of long, uniformly packed capillary columns capable of producing over 240,000 theoretical plates in SFC. Columns of up to 10 meters in length were prepared using LC packing materials of different chemical nature and particle size. The new method does not require a separate step for preparing the slurry, and it is free from the drawbacks inherent in conventional slurry‐packing methods. The lower viscosity and surface tension of carbon dioxide compared to conventional slurry‐forming liquids, as well as the use of ultrasonic vibration and pressure programming in the packing process, provide favorable conditions for achieving packing uniformity over greater column lengths than is achievable by other packing techniques. Proper restrictors and appropriate decompression rates during the use of these columns in SFC were found to be very important in achieving optimum column performance. In comparison to the use of open tubular columns, higher effciencies, greater sample capacities, and faster analysis speeds can be obtained. These advantageous features make the newly developed columns suitable for trace analysis, separation of very complex mixtures, and analysis of difficult‐to‐separate solutes.
Correlation of resolution with frictional coefficients and pKavalues in capillary electrophoresis of four diuretics: Determination of electric field strength and electroosmotic velocity
Authors: Jumppanen Juho H. , Sirén Heli , Riekkola Marja‐Liisa , Söderman Olle
Published: May 2005

Under ideal conditions in capillary zone electrophoresis, the frictional coefficients (f) and pKavalues of the analytes can be used to predict their separation under various conditions. These parameters can also be used to determine whether or not the separation depends solely on electrophoretic mobilities. Moreover, marker compounds with known electrophoretic mobilities can be used in ideal systems to yield information on pKavalues or on frictional coefficients for molecules at infinite dilution that cannot be studied by more widely used techniques. Fourier transform pulse gradient spin‐echo nuclear magnetic resonance spectroscopy is a standard method for measuring diffusion coefficients, from which the frictional coefficients were obtained. The good correlation between measured values of f and the observed elution times of four diuretics at pH 10.6 (20°C, CAPS 0.06 M) proved that the separation was based on the electrophoretic mobilities only. To be able to study the system accurately, the field strength and electroosmotic flow were measured empirically by using acetazolamide and clopamide as markers. The electric field strength in the electrolyte was found to be approximately 20% lower than expected. Simple equations are presented, which allow the measurement of these two quantities with the help of two compounds of known electrophoretic mobilities. To yield reliable results, the compounds should have electrophoretic mobilities differing by a factor of 2 or more.
Micro‐FFF: Theoretical and practical aspects of reducing the dimensions of field‐flow fractionation channels
Authors: Giddings J. Calvin
Published: May 2005

The value of miniaturizing field‐flow fractionation (FFF) channels is examined based on theoretical and experimental evidence. While FFF and chromatography are dynamically similar, the dimension analogous to capillary or particle diameter in chromatography is the Brownian excursion distance (ℓ), a "soft" dimension controlled by field strength and thus subject to significant reduction by increasing the field strength. Optimization of the “hard” channel dimensions (length, breadth, thickness) is a more complex matter involving diverse factors including sample dilution and detectability, clog‐free operation, edge effects, relaxation time, compatibility with pump and detector systems, and only in some cases the influence of these dimensions on the achievable ℓ.
Buckminsterfullerene as a stationary phase in liquid chromatography
Authors: Jinno Kiyokatsu , Fukuoka Katsunori , Fetzer John C. , Biggs Wilton R.
Published: May 2005

Buckminsterfullerene C60 was used as a stationary phase for the microcolumn liquid chromatographic separation (LC) of various aromatic compounds. Carbonaceous material prepared by a general soot production process was extracted with toluene, purified using several chromatographic processes, and then packed into fused silica capillary columns for chromatographic evaluation. The performance and separation characteristics were examined. The results indicate that the C60 fullerene can be useful as an LC stationary phase and offers a unique shape selectivity for aromatic compounds as compared to conventional octadecylsilica phases.
Application of capillary electrophoresis to the quality control of pharmaceutical formulations: Effect of area correction on quantitation of antitussives
Authors: Korman Milos , Vindevogel Johan , Sandra Pat
Published: May 2005

The application of capillary electrophoresis for assaying the drug content of pharmaceutical formulations has been studied. Correction of area for migration times has been found useful in those cases where environmental conditions lead to increased migration time variability. From the results, the feasibility of single‐point calibration with an external standard was shown and experimentally verified.