The apparatus function of quantitative differential thermal analysis,including heat convection and radiation

The apparatus function, i.e. the response of the equipment to a heat pulse, is derived for DTA instruments where, besides heat conduction, convection and radiation are considered. The solution of the heat-balance equation is described by a superposition of two exponential functions, which leads to the dependences of the calibration factor and the time constants on the heat capacity, the heating rate and the temperature. For the experimental determination, the relations are transformed into expressions which can easily be obtained from the calibration measurements.

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Zusammenfassung Die Apparatefunktion, das ist die Reaktion der Anordnung auf einen Heizimpuls, wird für eine Differential-Thermo-Anlage abgeleitet, wobei neben Wärmemeitung auch -Konvektion und-Strahlung zugelassen sind. Die Lösung der Wärmebilanzgleichung wird durch die Überlagerung zweier Exponentialfunktionen beschrieben, wobei sich die Anhängigkeiten des Gerätefaktors und der Zeitkonstanten von der Wärmekapazität, der Heizrate und der Temperatur ergeben. Zur experimentellen Bestimmung werden die Ausdrücke zu leicht aus den Kalibrierungsmessungen zugänglichen Größen aufbereitet.

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— , , , . , , . , .

     

Zur gas-chromatographischen Analyse strahlenchemischer Reaktionsprodukte

Zusammenfassung Strahlenschemische Reaktionsprodukte sind für die gaschromatographische Analyse als komplizierte Mischungen zu betrachten. Große Flüchtigkeits- und oft extreme Konzentrationsunterschiede zwischen den Komponenten erschweren die Analyse und erfordern die Anwendung spezieller Methoden und Techniken der Probenvorbereitung und-aufgabe sowie der Trennung und Bestimmung nur der wirklich interessanten Komponenten. Doppelsäulentechniken unter Einbeziehung von heartcutting, backflushing und trapping in geschlossenen, automatisch steuerbaren Apparaturen spielen dabei eine wichtige Rolle.

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Gas chromatographic analysis of reaction products from chemical irradiation

Summary The products of chemical irradiation can be regarded, from the gas chromatographic point of view, as being complex mixtures whose analyses are made difficult by the large differences in volatility and concentration of the various components. Special techniques must be used in the sample preparation and introduction as well as in the exclusive separation and determination of the components of particular interest. An important rôle in this process is played by double column techniques with heartcutting, backflushing and trapping in an automatically controlled closed system.

     

Studies of copper-modified V?Mo oxide catalyst for acrolein oxidation to acrylic acid

Modification of a V–Mo oxide catalyst by copper improves its catalytic properties due to the formation of a variable composition V–Cu–Mo–O phase with varying the ratio Mo/Me (Me=V+Cu).

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T–Cu–Mo–O, Mo/Me, Me=V+Cu.

     

Reduction of benzylideneaniline over supported Pd catalysts

In this work we have carried out a study on the liquid phase hydrogenation of benzylideneaniline, using dihydrogen over various supported Pd catalysts. Benzyl-ideneaniline reduction can be classified as insensitive to the catalyst structure. On the other hand, no compensating effect has been observed in performing the reaction over different supported Pd catalysts.

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Pd , . . Pd , .

     

Identifiability of first order reaction systems

The question of the possibility to determine all the unknown parameters of kinetic models is considered. A simple algebraic condition for structural identifiability in first order reaction systems is given.

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. .

     

Kinetics of thermal dehydration of Ba(ClO3)2 · H2O

The kinetics of thermal dehydration of microcrystalline powders and single-crystals of barium chlorate monohydrate were studied by differential scanning calorimetry. The computer elaboration of thermal data showed that a single kinetic law could not account for the whole decomposition; moreover, different laws had to be used for powders than for single-crystals, whose reaction appeared diffusion-limited towards the end of the dehydration. Optical microscopy was extensively used as an independent source of information to clarify some of the thermal results and to gain a deeper insigth into the possible reaction mechanism.

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Zusammenfassung Die Kinetik der thermischen Dehydratisierung mikrokristalliner, Pulver und einzelner Kristalle von Bariumchlorat Monohydrat wurde mittels Differential-Abtastkalorimetrie untersucht. Die Computerverarbeitung der thermischen Angaben zeigte, dass für die vollständige Zersetzung nicht ein einziges kinetisches Gesetz gültig ist, sondern, dass für Pulver, bzw. für einzelne Kristalle, deren Reaktion gegen Ende der Dehydratisierung als diffusionsbegrenzt erscheint, verschiedene Gesetze eingesetzt werden müssen. Als unabhängige Informationsquelle wurde die optische Miskroskopie weitläufig eingesetzt um einige thermische Ergebnisse zu klären und eine tiefere Einsicht in den möglichen Reaktionsmechanismus zu gewinnen.

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Résumé La cinétique de la déshydratation thermique du chlorate de baryum monohydraté en poudres microcristallines et en monocristaux, a été étudiée par analyse calorimétrique différentielle (DSC). L'évaluation des données thermiques par ordinateur a montré qu'une seule loi cinétique n'était pas applicable à l'ensemble de la décomposition; de plus, dans le cas des poudres, on doit appliquer des lois différentes de celles des monocristaux dont la réaction paraît être limitée, vers la fin de la déshydratation, par la diffusion. La microscopie optique a été largement utilisée comme source indépendante d'information afin de clarifier certains résultats thermiques et d'acquérir une connaissance plus profonde du mécanisme probable de la réaction.

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. , , , . , , .

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The authors are indebted to Prof. Enzo Ferroni for helpful advice and to C.N.R. for financial support.     

Competitive hydrogenation of binary olefin mixtures in the liquid phase

The effect of a series of alcohol solvents on the selectivity of the competitive catalytic hydrogenation of 1-hexene and 2-methyl-3-butene-2-ol on Pt/SiO₂ catalyst has been investigated. With increasing molecular mass of the alcohol, the rate of hydrogenation of 1-hexene becomes relatively preferred; the same was observed also with branched alcohols compared with those having a straight chain. Systems were found in which the degree of coating of the platinum catalyst with copper affected (or did not affect) the selectivity of the competitive hydrogenation of pairs of olefinic substrates.

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— — 1- 2--3--2- Pt/SiO₂ . 1-, . , ( ) .

     

An improved method for the determination of the input applied to a linear system by deconvolution of the output. Application in thermokinetics

A simplified deconvolution procedure which can be used to remove the distortion, due to thermal lags, from calorimetric data is described and tested. The procedure is based on the state function theory. Noise in the deconvoluted data can be abated by smoothing the experimental data and by a careful choice of the data-sampling frequency. The method is adaptable to on-line processing by means of a microprocessor.

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Zusammenfassung Ein vereinfachtes Dekonvolutionsverfahren, das sich zur Behebung von infolge thermischer Lag-Erscheinungen auftretenden Zerrungen kalorimetrischer Daten eignet, wird beschrieben und getestet. Das Verfahren beruht auf der Theorie der Zustandsfunktion. Geräusche der Dekonvolutionsdaten können durch Ausgleichen der Versuchsdaten und durch sorgfältige Wahl der Datennahme-Frequenz gedämpft werden. Die Methode kann mittels eines Mikro-Verarbeiters zur on-line Verarbeitung eingesetzt werden.

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Résumé Une procédure simplifiée de déconvolution qui peut être utilisée pour éliminer des courbes calorimétriques, la distorsion causée par l'inertie thermique du calorimètre, est décrite et testée. La procédure est basée sur la théorie des variables d'état. Le bruit de fond des courbes corrigées peut être diminué par le lissage des données expérimentales et par le choix d'une fréquence d'échantillonnage appropriée. La méthode peut être adaptée au traitement en ligne des données au moyen d'un microprocesseur.

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, , ** . . ** . ** on-line.

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The authors gratefully acknowledge the assistance of Dr. J. Van Bokhoven, Chemisch Laboratorium TNO, Rijswyk, the Netherlands, during the experimental part of this work.     

Nature of ethylene complexes on the surface of Ag/SiO2 as evidenced by13C NMR data

The formation of -complexes of C₂H₄ with Ag⁺ on oxidized Ag/SiO₂ catalysts is shown by¹³C NMR. These complexes are similar in nature to those of olefins with silver in solution.

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¹³C , Ag/SiO₂ - C₂H₄ Ag⁺, - .

     

Sensitivity of the solution of kinetic differential equation systems to the variations in the initial state exemplified by liquid-phase chain oxidation of hydrocarbons

The influence of the initial states on the solution of the system of differential equations for the chain mechanism of liquid phase hydrocarbon oxidation has been studied.

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, .

     

Estimation of silanol groups in silica-based packings for liquid chromatography from gas chromatographic retention of cyclohexane and benzene

Summary Gas chromatographic retention of cyclohexane and benzene on microcolumns packed with silica-based materials for liquid chromatography has been investigated to elucidate the relationship with the surface properties of the packing materials. Differences in capacity factors (k) for these two hydrocarbons were related to the surface area of the packing materials. For untreated silica gels, the k value increased with increasing total surface area of the column employed and measurement of k for chemically-bonded stationary phases allowed estimation of accessible residual silanol groups.     

Quantum chemical studies of ethylene addition to organoaluminium compounds

In terms of the MINDO/3 method, the surface potential energy of ethylene addition to AlH₃ and Al(CH₃)₃ has been calculated.

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MINDO/3 AlH₃ Al(CH₃)₃.

     

Total chromatographic optimization (TOCO) II. Precision and efficiency of analysis

Summary A chromatographic system set at an operating condition takes its own precision and efficiency which are numerically described by the information called FUMI and the information flow , respectively. Optimization for a variable such as mobile phase composition draws a line in the - space. This paper demonstrates that optimization of different variables displays different patterns of lines in the - space. The variables examined here are mobile phase composition, column length, flow rate (velocity) and detection wavelength (or the amount of internal standard). Clear difference in the analytical roles of the variables can be known from the - plots.     

Liquid chromatography of cyclodextrins with indirect photometric detection of phenolphthalein inclusion complexes

Summary - and -cyclodextrin (CD) separated by liquid chromatography have been indirectly detected by depression of the background absorbance at a visible wavelength by means of inclusion complexation with phenolphthalein. The background signal was generated by phenolphthalein in an alkaline medium. Octadecyl-bonded poly(vinylalcohol) packings were employed as the stationary phase, which allowed the use of alkaline mobile phases, and eliminated post column mixing of reagents. The detection limits for - and -CD were 0.1–0.5 M at a signal to noise ratio of 3. -CD could not be measured by the present detection principle.     

The GC separation of C2-naphthalene isomers using cyclodextrins and crown ethers

Summary The twelve structural C₂ isomers of naphthalene are resolved on a single capillary column using , , or cyclodextrin as the stationary phase. A change in elution order is seen upon going from to and then cyclodextrin which can be related to the size of the cyclodextrin cavity and the stereochemical fit of the isomer. A crown-ether column and a liquid-crystal column were found to be unable to separate all of the isomers.     

Activation of ruthenium on silica hydrogenation catalysts

Activation of RuCl₃-impregnated silica by nitrogen-hydrogen tratment at high temperature, up to 700 °C, is superior to calcination of the material prior to reduction. Sintering hardly occurs. In addition, activity measurements, based on the liquid phase hydrogenation of benzene, and thermogravimetric analysis suggest a favorable (chemical) interaction between ruthenium and silica.

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, RuCl₃ 700°C . . , , () .

     

Total chromatographic optimization (TOCO) I. Simultaneous optimization of many variables in liquid chromatography

Summary The following chromatographic variables are totally optimized based on the recently developed information theory of optimization: mobile phase composition, column length, flow rate, wavelength, and the amount of internal standard. The optimal internal standard is selected from among six candidates. Two types of optimal conditions (- and -optimals) are proposed: the -optimal is defined as the most precise analysis (the maximal ) while the -optimal is the most efficient (rapid) analysis (the maximal ). The observation times for the determination of an antipyretics mixture (three components) in liquid chromatography are ca. 50 s for the -optimal and ca. 8 min for the -optimal. The reliability of the - and -optimals is verified by experiments.     

Studies on water retention and water release from some protein systems

The hydrogen-bond properties (WBI index), water retention and water release from the protein-water systems gluten-water, soya protein- water and casein-water, have been investigated using differential scanning calorimetry in the temperature range 223–423 K. The proteins were characterized by their isoelectric point, contents of carboxyl groups and sulfur-containing groups, and readiness of undergo chloromethylation. It was concluded that the marked difference in water-release behaviour is chiefly explained by conformational differences and charge effects.

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Zusammenfassung Wasserstoffbrückenbindugseigenschaften (WBI-Index), Wasserretention und Wasserabgabe von Protein-Masser-Systemen — Gluten-Wasser, Sojaprotein-Wasser und Casein-Wasser — wurden im Temperaturbereich von 233–423 K mit einem Scanning-Kalorimeter untersucht. Die Proteine wurden durch ihren isoelektrischen Punkt, den Gehalt an Carbonylgruppen und Schwefel enthaltenden Gruppen und durch ihre Reaktivität in der Chlormethylierung charakterisiert. Es wurde gefolgert, dass der ausgesprochene Unterschied im Wasserabgabeverhalten in erster Linie auf strukturelle Unterschiede und Ladungseffekte zurückzuführen ist.

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223–423 K , , — , — — . , , . , .

     

New model of the hydroxylating enzyme system of liver microsomes: NADH-riboflavine-hemoglobin-O2

The kinetics of aniline hydroxylation to p-aminophenol by the NADH-riboflavine-hemoglobin-O₂ system has been investigated in a phosphate buffer (pH 6.8) at 37°C. At optimal concentrations of the model system components the rates of aniline oxidation are comparable with those of the enzymatic hydroxylation of aniline by rat liver microsomes. Possible paths of aniline hydroxylation in the system NADH-riboflavine-hemoglobin-O₂ are discussed.

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37°C pH 6,8 - .---O₂. . .---O₂.

     

Interaction of cyclodextrins with drugs. Chromatographic investigation using a cyclodextrin bonded-phase and its application to chiral separations

Summary The interaction between cyclodextrin and the drug (1R,2S,3S,4S)-(5Z)-7-(3-((phenylsulfonyl)amino)bicyclo[2.2.1]hept-2-yl)hept-5-enoic acid ((+)-S-145), was studied using -, -, and -cyclodextrin bonded-phase columns. Retention behavior of (+)-S-145 on these columns revealed that the strength of inclusion was -cyclodextrin. Interaction between -cyclodextrin and (+)-S-145 was found to increase as the proportion of carboxylic ion in the (+)-S-145 molecule increased. Comparison of binding capacities of these bondedsilica gels obtained by frontal analysis and surface coverage indicated that availability of the immobilized - and -cyclodextrin was 20–25%. The synthesized -cyclodextrin bonded-phase column was superior to that of commercial columns in terms of chiral separation of (±)-S-145. A typical usage of the -cyclodextrin column is discussed for separation of (±)-S-145 in plasma samples.