Reproducibility of glass open tubular columns in a production environment — Two years of experience

Summary The problems associated with the preparation of glass open tubular (capillary) columns are well documented in the literature. These problems are even more evident if column production is done on a routine basis, in a production environment. On the other hand, from the point of the user who wants to rely on a supplier, the reproducible quality of the columns is crucial. Here quality does not only mean efficiency but also refers to the reproducibility of the average liquid film thickness (capacity ratio) and the relative retention, as well as the tube treatment influencing the polarity of the column tube. In a paper published one year ago [1] our investigation concerning the reproducibility of the column manufacturing process was reported. The present paper continues this investigation. Four different columns will be considered: two types of OV-101 columns with thin and thick liquid film as well as columns prepared with Carbowax 20M and DEGS liquid phases. The consistency of their characteristics and efficiency will be investigated. Column characteristics include the capacity ratio which is directly related to the thickness of the liquid phase film. Column efficiency is investigated with help of the HETP and peak resolution. The effective and theoretical plate numbers are compared and the incorrectness of the assumption that the former is better suited for column testing is demonstrated. Relative retention reproducibility of even difficult peak pairs shows the consistency of column wall treatment. Finally, the consistency and performance of shorter columns obtained by the breaking of long columns will be discussed.Paper presented at the Second International Symposium on Glass Capillary Chromatography, Hindelang, Allgäu, Federal Republic of Germany, May 2–6, 1977.     

Stéréochimie des réactions de substitution des alcoxygermanes par les organolithiens et par les réactifs de Grignard

The reactions of organolithium reagents and Grignard reagents with optically active alkoxygermanes R₃GeOR′ have been studied [R₃GeOR′ = ()-i-PrPhNpGeOCH₃, ()-i-PrPhNPGeOMen and ()-MePhNpGeOMen]. Saturated reagents (e.g. butyllithium) give retention of configuration at germanium whilst unsaturated reagents (e.g. allyl- or benzyllithium) lead to inversion.     

Synthese und Konfiguration von Methylestern der diastereomeren (±)-3-Amino-2,3-diarylpropansäuren,der (±)-3-Amino-2,3-diarylpropanole und ihrer Derivate

Zusammenfassung Durch Umsetzung von Hydramiden mit am aromatischen Ring m,p-dialkoxysubstituierten Arylessigsäureestern in Gegenwart von wasserfr. AlCl₃ entstehen Gemische aus Estern der (±)-erythro- und (±)-threo-3-Amino-2,3-diarylpropansäuren. Bei der Umsetzung von Piperonalhydramid mit dem Methylester der Homoveratrumsäure konnte lediglich daserythro-Diastereomere isoliert werden.Die diastereomeren Ester wurden zu den jeweiligen (±)-erythro- und (±)-threo-3-Amino-2,3-diaryl-1-propanolen reduziert, die als N,O-Dibenzoylderivate charakterisiert wurden. Ihre relativen Konfigurationen und die der zugehörigen Ester wurden auf Grund der IR-Spektren der diastereomeren Aminopropanole bestimmt. Die NMR-Spektren eines Diastereomerenpaares von Aminopropanolen bestätigen die ihnen chemisch zugeordneten Konfigurationen und ermöglichen den Nachweis auch ihrer bevorzugten Konformationen.

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Synthesis and configuration of methyl esters of the diastereomeric (±)-3-amino-2,3-diarylpropanoic acids, the (±)-3-amino-2,3-diaryl-1-propanols and their derivatives

Reaction of hydramides with m,p-dialkoxysubstituted arylacetates in the presence of anhydrous AlCl₃ generally leads to mixtures of the esters of the (±)-erythro- and (±)-threo-3-amino-2,3-diarylpropanoic acids. However, in the reaction of piperonal hydramide with methyl homoveratrate, only the correspondingerythro-diastereomer was obtained.Reduction of the diastereomeric esters gives the corresponding (±)-erythro- and (±)-threo-3-amino-2,3-diaryl-1-propanols, which can be characterized as N,O-dibenzoyl derivatives. Relative configurations of both alcohols and esters were determined by means of their IR spectra. Configurations were confirmed for one pair of diastereomeric amino alcohols by means of NMR spectra and preferred conformations deduced.

     

l-Leucanthemit als Inhaltsstoff von Gymnospermae

Zusammenfassung Die Bildung und das Vorkommen von Cycliten inThuja occidentalis wurden mit Hilfe der Methode der Photoassimilation in einer Atmosphäre von¹⁴CO₂ untersucht. Nebenmyo-Inosit, Sequoyit,d-chiro-Inosit undd-Pinit wurde auchl-Leucanthemit (l-1,2,4/3-Cyclohexentetrol), ein Cyclit, der bisher nur als Inhaltsstoff mehrerer Angiospermae bekannt ist, nachgewiesen. Das Vorkommen vonl-Leucanthemit konnte auch inPinus austriaca sichergestellt werden. Methoden zur Isolierung vonl-Leucanthemit ausThuja occidentalis wurden ausgearbeitet.

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The formation and the occurrence of cyclitols inThuja occidentalis has been studied, using the method of photoassimilation in an atmosphere of¹⁴CO₂. Besidesmyo-inositol, sequoyitol,d-chiro-inositol, andd-pinitol, alsol-leucanthemitol (l-1,2,4/3-cyclohexentetrol), a cyclitol which so far has only been found in Angiospermae, was identified. The occurrence ofl-leucanthemitol could also be established inPinus austriaca. Methods have been elaborated which permit the isolation ofl-leucanthemitol fromThuja occidentalis.

     

Photometric titrations. VIII

Summary Cadmium and zinc can be determined in one solution in the following manner. The sample is adjusted to p_H 9.4 with an ammonia-ammonium chloride buffer so that the total ammonia concentration is 0.01–0.03M. Zincon is added to attain a concentration of 0.06–0.18 mg/ml. The titration is performed photometrically at about 620 nm with EGTA as the titrant. The titration curve obtained shows two breaks which are related to the consecutive titration of cadmium and zinc. The influence of calcium impurities in the reagents used has been studied and a pre-titration method is proposed to deal with small calcium blanks. Calcium may also be added to the sample in order to obtain a titration curve which shows three breaks, which are related to the consecutive titration of cadmium, calcium, and zinc.

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Zusammenfassung Cadmium und Zink lassen sich nebeneinander in einer Lösung bestimmen. Man bringt die Probe durch Zusatz von Ammoniak-Ammoniumchlorid-Puffer auf p_H 9,4, so daß die totale Ammoniakkonzentration 0,01- bis 0,03-m ist. Pro ml werden 0,06 bis 0,18 mg Zincon zugesetzt, dann wird mit EGTA [Äthylenglykol-bis-(-aminoäthyläther)-N,N,N,N-tetraessigsäure] bei etwa 620 nm photometrisch titriert. Die Titrationskurve zeigt zwei Knickpunkte, die der aufeinanderfolgenden Titration von Cadmium und Zink entsprechen. Der Einfluß von Calcium-Verunreinigungen in den verwendeten Reagenzien wurde untersucht und eine Vortitration zur Bestimmung kleiner Calcium-Blindwerte vorgesehlagen. Man kann auch der Probe Calcium zusetzen und erhält dann eine Kurve mit drei Knickpunkten, entsprechend den aufeinanderfolgenden Titrationen von Cadmium, Calcium und Zink.

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Résumé On peut doser le cadmium et le zinc sur une seule solution de la manière suivante. On ajuste le p_H de l'échantillon à 9,4 par un tampon ammoniaque-chlorure d'ammonium de façon que la concentration totale en ammoniaque soit de 0,01–0,03M. On ajoute de la zincone jusqu'à l'obtention d'une concentration de 0,06–0,18 mg/ml. On effectue un dosage speetrophotométrique à 620 nm en utilisant l'EGTA comme agent titrant. La courbe de titrage montre deux points anguleux correspondant à la teneur en cadmium et en zinc. Après avoir étudié l'influence du calcium à l'état d'impuretés dans les réactifs utilisés, on propose une méthode de prétitrage pour faire les essais à blanc avec de petites quantités de calcium. On peut également ajouter du calcium à l'échantillon afin d'obtenir une courbe de titrage avec trois points anguleux relatifs aux titrages consécutifs du cadmium, du calcium et du zinc.

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See reference 1 for paper VII of the series.

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Dedicated to Prof.A. A. Benedetti- Pichler on the occasion of his 70th birthday.     

A study of thermal decomposition of the solid-layered fluorocarbon,poly(carbon monofluoride)

Isothermal-thermogravimetric analyses were used to obtain kinetic data on the CF_x decomposition. Weight of samplevs. time curves were obtained for compounds having stoichiometries CF_0,61, CF_0.96, CF_1.08, and CF_1.12 for several different temperatures over the range 450–650° and in both a nitrogen atmosphere and in vacuum. A small percentage of fluorine in the atmosphere was shown to strongly inhibit thermal decomposition.These experimental results were fit to various theoretical models and it was found that a satisfactory fit was obtained by use of the Avrami equation, -In(1–)=(kt)ⁿ, where is the extent of reaction,k is an apparent rate constant, andn is an apparent reaction order. The valuen=2.0 was indicated which corresponds to planar growth of the decomposed phase.This information was combined with analytical data for the gaseous and solid products of decomposition to formulate a detailed mechanism.

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Zusammenfassung Isotherm-thermogravimetrische Analysen wurden durchgeführt um kinetische Daten über die Zersetzung von CF_x zu erhalten. Probengewicht-Zeit-Kurven wurden für Verbindungen mit stöchiometrischen Verhältnissen von CF_0.61, CF_0.96, CF_1.08 und CF_1.12 bei verschiedenen Temperaturen im Bereich von 450° bis 650°, in Stickstoff sowie im Vakuum aufgenommen. Ein geringer Prozentsatz an Fluor in der Atmosphäre wirkte stark inhibierend auf die thermische Zersetzung.Diese Versuchsergebnisse wurden verschiedenen theoretischen Modellen angepasst und es wurde gezeigt, dass mit Hilfe der Avrami-Gleichung -In (1–)=(kt)ⁿ eine befriedigende Anpassung möglich ist, wobei =Ausmaß der Reaktion, k=scheinbare Geschwindigkeitskonstante undn=scheinbare Reaktionsordnung ist. Der angedeutete Wertn=2.0 entspricht einer planaren Zunahme der zersetzten Phasen.Diese Information wurde mit analytischen Daten der gasförmungen und festen Zersetzungsprodukte kombiniert um einen Mechanismus in allen Einzelheiten zu formulieren.

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Résumé La TG isotherme a été utilisée pour obtenir des données cinétiques sur la décomposition de CF_x. Les courbes donnant le poids de l'échantillon en fonction du temps ont été energistrées à différentes températures, entre 450 et 650°, en atmosphère d'azote et sous vide, sur des composés de composition CF_0.61, CF_0.96 et CF_1.08. Un faible pourcentage de fluor dans l'atmosphèere s'est avéré inhiber considérablement la décomposition thermique.Ces résultats expérimentaux ont été confrontés à divers modèles mathématiques. On a trouvé un ajustement satisfaisant à l'aide de l'équation d'Avrami, -In (1–)=(kt)ⁿ, où es l'avancement de la réaction,k une constante de vitesse apparente etn un ordre de réaction apparent. La valeurn=2.0 correspond à une croissance dans le plan de la phase décomposée.Cette information a été combinée avec des données analytiques sur les produits de décomposition gazeux et solides, afin de formuler un mécanisme détaillé.

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- CF_x. — CF_0.61, CF_0.96, CF_1.08 F_1.12 450°–650°, , . . , -1(1–)= (kt)ⁿ, — , k — , n — . n=2, . , .

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Abstracted in part from the Ph. D. thesis of Peter Kamarchik, Jr. Rice University, Houston, Texas, May, 1976.

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This work was supported financially by the National Science Foundation, the U.S. Army Research Office (Durham), the National Aeronautics and Space Administration, and the Robert A. Welch Foundation. Liquid helium was provided under a grant from the Office of Naval Research.     

Thermal investigations on the crystallization of sorbitol

The melting and crystallization of sorbitol were investigated with the DSC method and thermal microscopy. Sorbitol was found to have two crystalline modifications (confirmed by X-ray diffraction) with different melting points, while rapid cooling of molten sorbitol resulted in an amorphous form. The effect of inoculation on the crystallization of the melt was studied too. Powders of both crystalline modifications were used for this purpose. A new technological process for rapid crystallization of molten sorbitol has been worked out on the basis of the thermal analysis results.     

The biochemistry of cell-adhesion

The proposition is examined that adhesion between cells of animal tissues, and between cells and their extracellular matrix, is brought about by specific molecules present at cell-surfaces. Evidence is surveyed which has begun to emerge from the use of antibodies which inhibit or reverse adhesion. Putative cell-adhesion molecules in cellular slime-moulds and cells of chick and mouse embryos have been identified by their ability to neutralize the adhesion-inhibiting activity of monovalent fragments of polyspecific antibodies. In some instances antibodies have also been used to investigate the role of the cell-adhesion molecules in morphogenetic phenomena. A possible parallel is discussed between the effects of calcium ions on the cell-adhesion molecule uvomorulin from mouse blastomeres, and its effects on certain other cell-adhesion molecules.Although the role of fibronectin in promoting attachment and spreading of cells on artificial substrates and on denatured collagen is firmly established, there is little evidence that this glycoprotein is involved in direct intercellular adhesion. The observation that cells spread on adsorbed fibronectin, whereas binding of individual fibronectin molecules to cells is difficult to demonstrate may merely indicate that fibronectin is a relatively weak ligand for cell-surfaces. It is suggested that rather than being a necessary intermediate in the adhesion of cells to collagen, fibronectin may form matrix in its own right which shares with native collagen the ability to promote cell-attachment and spreading.The long-held view that cell-surface oligosaccharides act as receptors in cell-adhesion appears still to be largely unsubstantiated. However the poorly adhesive properties of cells from many different lines with glycosylation defects strongly suggest N-linked oligosaccharides of glycoproteins are involved in some way as yet not determined.     

Study of isotope exchange reactions by double labelling

This paper presents the method of double labelling in the study of the kinetics of homogeneous isotope exchange reactions. This method was tested by the determination of the Sn(II)−Sn(IV) exchange rate in hydrochloric acid medium. The system was labelled by the tracer^119mSn [initially in the Sn(IV) state]; when the isotope equilibrium was established, Sn(IV) was again labelled by tracer¹¹³Sn. The separation of Sn(II) and Sn(IV) in the given time of exchange was performed by the extraction of Sn(IV)-hydroxyquinolate into chloroform. The specific activities of the separated components were determined from the ratio of¹¹³Sn and^119mSn activities. The exchange rate was calculated from the time dependence of specific activities. The advantage and possibilities of the method of double labelling in the study of isotope exchange are discussed.