Application of programmed temperature decomposition to the study of solid decomposition reactions taking place through the prout and tompkins mechanism

A method has been developed to allow kinetic analysis of the Prout and Tompkins mechanism of solid decomposition reactions using a single TG diagram obtained in a linear heating program. On the other hand, provided that the nickel formate decomposition follows such a mechanism, this reaction has been used for checking the kinetic equation obtained.     

Biological fluid screening and confirmation of bile acids by use of an integrated flow-injection-LC-evaporative light-scattering system

Summary An integrated flow-injection-liquid chromatographic system is presented for the screening of biological fluids for bile acids, and for subsequent confirmation. It is based on the use of a flow-injection configuration with an evaporative light-scattering detector (ELSD), for routine screening for the total concentration of the analytes, followed by the individual determination, by liquid chromatography, of only those samples for which the total concentration is close to or above the normal level in healthy individuals. Bile acids are extracted from human serum and urine withn-hexane under acid conditions. After phase separation the organic layer is evaporated to dryness under a stream of nitrogen and redissolved in weakly alkaline solution (pH 8). The aqueous phase is then passed through a miniaturized Amberlite XAD-7 column for preconcentration and clean up, and eluted with acetonitrile-methanol, 65∶35 (v/v). The effluent is introduced directly into the ELSD for determination of the total bile-acid content of the sample. For confirmatory analysis another aliquot of the sample is processed in the screening module and the effluent from the adsorbent column is then directed to the chromatographic column to obtain the bile acid profile of the sample. Good agreement was obtained in the analysis of urine and serum samples by both procedures.     

Optimization of a microwave-assisted derivatization-extraction procedure for the determination of chlorophenols in ash samples

A procedure for the determination of 17 chlorophenolic compounds in ash samples obtained from the incineration of waste materials is described. Analytes were simultaneously derivatized with acetic anhydride in presence of triethylamine (TEA), and extracted from the sample in a mixture of n-hexane acetone using a microwave system equipped with closed extraction vessels. Influence of five experimental parameters (volume of TEA and acetic anhydride, extraction time and temperature, as well as the volume of n-hexane acetone) on the yield of the derivatization-extraction procedure was systematically studied using a uniform experimental design at four levels, followed by a conventional factorial design at two levels. Under optimal extraction conditions, recoveries from 72 to 94% were obtained for a spiked ash sample with a carbon content of 8.7%. Quantification limits of the proposed procedure ranged from 2 to 5 ng/g using GC-MS as detection technique. The proposed method was applied to the determination of chlorophenols in three ash samples obtained from different incineration plants. Total chlorophenol contents of 423 and 135 ng/g were found in two of these samples.     

Influence of the Co2 pressure on the kinetics of thermal decomposition of manganese carbonate

Kinetic analysis has been performed on TG and DTG diagrams of the forward reaction MnCO₃ MnO + CO₂, recorded at different pressures of CO₂ ranging form 2.6. 10^–4 Pa to 26.6 kPa. The results obtained show that this reaction follows a first-order kinetic law, independently of the CO₂ pressure used in carrying out the experiments. On the other hand, the activation energy increases on increase of the CO₂ pressure, from 117 kJ/mol up to an asymptotic value of 292 kJ/mol at about 26.6 Pa. This finding cannot be explained by considering the influence of the reverse reaction of formation of MnCO₃, for under the described experimental conditions the ratio to zero. A mechanism that takes into account the adsorption of CO₂ on the phase boundary has been proposed in order to interpret the results.

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Zusammenfassung Die kinetische Analyse der Reaktion MnCO₃ MnO + CO₂ in Richtung des oberen Pfeiles wurde an Hand von TG und DTG Diagrammen durchgeführt, welche bei verschiedenen CO₂-Drucken im Bereich von 2.6·10^–4 bis 26.6 kPa aufgenommen wurden. Die erhaltenen Ergebnisse zeigen, daß diese Reaktion einem kinetischen Gesetz erster Ordnung folgt, unabhängig von dem zur Durchführung der Experimente angewandten CO₂-Druck. Andererseits nimmt die Aktivierungsenergie mit steigendem CO₂-Druck von 117 kJ/mol bis zu einem asymptotischen Wert von 292 kJ/mol bei etwa 26 660 Pa zu. Dieses Ergebnis kann unter Berücksichtigung der Umkehrreaktion der MnCO₃-Bildung nicht erklärt werden, da unter den beschriebenen Versuchsbedingungen das Verhältnis , sehr nahe zu Null ist. Um die Ergebnisse zu deuten wurde ein Mechanismus vorgeschlagen, welcher die Adsorption des CO₂ an der Phasengrenzfläche berücksichtigt.

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MnCO₃ n + + ₂, ₂ 2.6 · 10^–4 26.6 . , , ₂ . , , ₂, 117 / 292 / 26.6 . , . . ₂ .

     

Computer kinetic analysis of simultaneously obtained TG and DTG curves

The computer kinetic analysis of simultaneously obtained TG and DTG curves of CaCO₃ decomposition has been carried out. Ten different kinetic equations have been tested to decide the mechanism which drives the reaction. Either a two-thirds kinetic equation (phase boundary process) or a Jander equation (diffusion process) satisfactorily describe the kinetic data of both decomposition curves. From these results we conclude there is no chance of differentiating between these two mechanisms by only the kinetic analysis of TG and DTG curves separately.A better approach to the problem is possible if the kinetic analysis is performed on simultaneous TG and DTG curves, together with an isothermal one. This procedure might be a valid way to establish the mechanisms of thermal decomposition reactions by means of kinetic methods without additional information.

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Zusammenfassung Es wurde die kinetische Analyse simultan erhaltener TG- und DTG-Kurven der Zersetzung von CaCO₃ mittels Computer durchgeführt. Zehn verschiedene kinetische Gleichungen wurden zur Ermittlung des reaktionssteuernden Mechanismus erprobt. Die kinetischen Daten beider Zersetzungskurven können entweder durch eine Zwei-Drittel kinetische Gleichung (Phasen-Grenzflächenprozess) oder eine Jander-Gleichung (Diffusionsprozess) befriedigend beschrieben werden. Aus diesen Ergebnissen wird gefolgert, dass keine Möglichkeit besteht diese beiden Mechanismen ausschliesslich durch die kinetische Analyse der TG- und DTG-Kurven von einander zu unterscheiden. Eine bessere Annäherung an das Problem ist durch die kinetische Analyse simultaner TG- und DTG-Kurven gemeinsam mit einer isothermen Kurve möglich. Dieser Vorgang erscheint als ein möglicher Weg zur Unterscheidung der Mechanismen thermischer Zetsetzungsreaktionen an Hand kinetischer Methoden ohne Zusatzliche Information.

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Résumé L'analyse cinétique des courbes TG et TGD obtenues simultanément lors de la décomposition de CaCO₃ a été effectuée à l'aide d'un ordinateur. Dix équations cinétiques différentes ont été examinées pour établir le mécanisme moteur de la réaction. L'équation cinétique de type 2/3 (processus d'interface) ou l'équation de Jander (processus de diffusion) décrivent toutes deux de maniÊre satisfaisante les données cinétiques déduites des courbes TG et TGD. De ces résultats on conclut qu'il n'est pas possible de distinguer ces deux mécanismes en s'appuyant exclusivement sur l'analyse cinétique des courbes TG et TGD.Une meilleure approche du problÊme est possible si l'on effectue l'analyse cinétique des courbes TG et TGD simultanées en mÊme temps que celle d'une courbe isotherme. Ce procédé peut Être un bon moyen pour élucider le mécanisme des réactions de décomposition thermique à l'aide de méthodes cinétiques, sans informations supplémentaires.

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The authors' thanks are due to Dr. Delia Balbontin for her assistence with the computer, and Dr. I. Carrizosa for his helpful discussions.     

Some considerations regarding the determination of the activation energy of solid-state reactions from a series of isothermal data

It has been demonstrated that the kinetic data on solid-state reactions show a good fitting to the expressiong(α)=kt, regardless of the nature of theg(α) function previously assumed for performance of the calculations. Moreover, the activation energy value obtained from the Arrhenius law is quite independent of the kinetic function assumed.     

Oxidation of bis(4-toluenesulphonyl-L-serinato)copper(II) to bis(formylglycine)copper(II)

Summary Oxidation of L-serine occurs on degradation of bis(L-serinato)copper(II) and at the same time copper is reduced.     

Use of Emanation Thermal Analysis in Characterisation of Nanosized Hematite Prepared by Dry Grinding of Goethite

Hematite nanoparticles of narrow size distribution were prepared by grinding of goethite. Intermediate and final products of grinding were characterised by different techniques, including the less-common emanation thermal analysis (ETA). ETA was shown to be a useful technique for characterising processes of surface annealing, initial sintering and growth of hematite particles under in situ conditions of thermal treatment. A good agreement was found between results of ETA, TG, XRD, IR spectrometry, transmission electron microscopy and scanning electron microscopy, used for characterisation of thermal behaviour of the goethite samples ground for varying time (0–70 h). This revised version was published online in August 2006 with corrections to the Cover Date.