Correction in DTA purity determination

An equation for calculating the melted fraction (F) in purity determinations by DTA has been derived, which makes a correction for the thermal lag of the sample cell during the melting process. A set of samples of benzoic acid containing different quantities of anthracene has been tested. There are two peaks in the melting thermograms and the calculated impurity contents in these samples without using the correction are less than those prepared. This binary system is assumed to form an eutectic; its composition and melting point are estimated as X = 0.056 mole fraction of anthracene and T = 117.8°C respectively. Results obtained using naphthalene containing 0.415 mol% of fluorene show that the correction for the thermal lag of sample cell is necessary. In addition, a linear correction in the F calculation for the melting of eutectic and premelting of the main component is also desirable, giving a good straight line of the melting temperature T versus 1/F and a reasonable purity estimation.     

DTA determination of specific heats of liquids

A method is described for conversion of the experimentally measured total heat capacity of a sample of low-boiling liquid, heated in a closed, pressure-proof pan, to its specific heat.     

Non-aqueous determination of inorganic salts

The procedures suggested for the determination of salts in nonaqueous solutions have been limited almost wholly to the analysis of amine salts and salts of the alkali and alkaline earth metals. Other salts are usually assayed by a variety of specific cationic or anionic procedures. By the proposed method, salts of all types can be determined titrimetrically so long as the compound will participate in an anion-exchange reaction. The procedure simply involves acidification of the salt with an excess of a strong acid, addition of a nonaqueous solvent and a differentiating potentiometric titration. Carbonate and hydroxide impurities do not interfere in the analysis and the solubility difficulties experienced in other nonaqueous procedures are not encountered in this method.     

Micro-gasometric determination of water in hydrated salts

Summary The method ofElitsur for gasometric determination of water in hydrated salts by the liberation of hydrogen resulting from the interaction between calcium hydride and hydrated salt in pyridine medium has been made applicable to micro scale by the use of suitable apparatus and procedure.Determinations of water of hydration are reproducible within 0.3% H₂O of the theory.

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Zusammenfassung Das gasvolumetrische Verfahren vonElitsur, das auf der Entbindung von Wasserstoff beim Erhitzen der wasserhältigen Substanz mit Pyridin und Calciumhydrid beruht, wurde durch Wahl eines geeigneten Apparates und eines Vorgehens zur Entfernung von Feuchtigkeitsspuren aus Apparat und Reagensmischung unmittelbar vor Beginn der Bestimmung für die Ausführung im Mikromaßstab geeignet gemacht. Bestimmungen von Kristallwasser können innerhalb 0,3% H₂O vom Sollwert ausgeführt werden.

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Résumé L'emploi d'un appareil et d'une technique convenables a permis d'étendre à l' échelle microanalytique la méthode deElitsur pour le dosage gazométrique de l'eau dans les sels hydratés par dégagement d' hydrogène résultant de leur réaction sur l'hydrure de calcium en milieu pyridinique.Les résultats obtenus sont reproductibles et diffèrent de moins de 0,3% H₂O des résultats théoriques.

     

On the method of bae for the determination of kinetic parameters from DTA curves

The mathematical error in the method proposed by Bae for the determination of kinetic parameters from DTA curves has been corrected. The proposed equation does not contain thermal constants of the apparatus, and can be applied to DTA curves by an iterative method. The results obtained by the application of this equation to experimental DTA curves for the decomposition of sodium bicarbonate compared well with those from isothermal measurements, even when the DTA sample holder assembly was of the isolated cup-type instead of the block-type assembly recommended by Bae.     

A systematic error in the temperature determination of a DTA effect by using the onset point

Journal of Thermal Analysis and Calorimetry - The Committee on Standardization of the ICTA proposed a method for determination of the temperature of a DTA effect. This procedure is easy to perform,...     

Extraction-spectrometric determination of lead in high-purity aluminium salts

Trace amounts of lead were determined in high purity aluminium salts (especially in ammonium aluminium sulfate) using inductively coupled plasma-optical emission spectrometry (ICP-OES) after extractive pre-concentration and matrix separation. Metals were extracted from the aluminium matrix in the form of chelates with ammonium pyrolidine dithoocarbamate into methyl isobutyketone. The organic extract was digested with nitric acid and hydrogen peroxide. The limit of detection for the determination of lead in crystalline ammonium aluminium sulfate was ca. 0.044 mug g(-1). The relative expanded uncertainty of the lead determination was ca. 23% at the level of 0.2 mug g(-1) and ca. 16% at the level of 1.0 mug g(-1). The main uncertainty contribution was associated with repeatability of the whole analytical procedure.     

Application of DTA to the determination of the properties of mixed monolayers on solid surfaces

Journal of Thermal Analysis and Calorimetry - Differential thermal analysis was used as a complementary method to “inverse” gas chromatography in the investigation of phase transition...     

Substoichiometric determination of uranium in phosphate rock

The substoichiometric isotope dilution analysis for U(VI) in a synergic extraction system of an excess amount of a chelating agent HHFA and a substoichiometric amount of neutral ligand TOPO has been developed. A constant but substoichiometric amout of U(VI) can be precisely extracted, and U down to ppm levels can be accurately determined by the present method. This method was applied to the analysis of a phosphate rock.     

Coulometric determination of carbonates in rock samples

Summary A commercially available carbon analyser based on the coulometric alkalimetric titration was adapted for the determination of carbonates in rocks and minerals. Wet decomposition of samples with concentrated phosphoric acid is used. The developed procedure enables the selective determination of carbonates in a broad concentration range in samples containing non-carbonate carbon, sulphides, fluorides, borates and low contents of chlorides.

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Coulometrische Bestimmung von Carbonat in Gesteinsproben

Zusammenfassung Ein handelsüblicher Kohlenstoffanalysator, der auf der coulometrisch-alkalimetrischen Titration beruht, wurde für die Carbonatbestimmung in Gesteinen und Mineralien angepaßt. Der Naßaufschluß der Proben erfolgte mit konz. Phosphorsäure. Das Verfahren gestattet eine selektive Carbonatbestimmung in verschiedenartigen Proben, die Nichtcarbonat-Kohlenstoff, Sulfid, Fluorid, Borat sowie kleinere Mengen Chlorid enthalten.

The author wants to express his thanks to Dr. Z. ulcek CSc. and Mr. M. Huka for valuable advices and discussions during the experimental work.     

Extraction-visible spectrophotometric method for the determination of tetraphenylphosphonium salts

Das empfindliche und relativ einfache Verfahren beruht auf der Extraktion des Tetraphenylphosphonium-Kations mit dem Vanadium(V)-4-(2-pyridylazo)-resorcin-Komplex und Absorptionsmessung der gefärbten organischen Phase bei 560 nm (molarer Extinktionskoeffizient 3,9 · 10⁴ l · mol^?1 · cm^?1). Das Lambert-Beersche Gesetz wird im Bereich von 1 · 10^?6 ?5 · 10^?5 M Tetraphenylphosphonium im Extrakt befolgt. Die relative Standardabweichung beträgt ±2% im Bereich von 10^?5 M und 5–10% im Bereich von 10^?6 M. Die Methode ist empfindlicher und weniger störanfällig als die direkte UV-Methode.     

Determination of water content of hygroscopic lithium salts

Determination of the water content in hygroscopic lithium chloride, lithium bromide, lithium nitrate and lithium sulfate by Karl Fischer reagent (KFR), Hydranal (Eugen Scholz reagent) and by thermal-vacuum drying is discussed. Agreement between the results of the KFR titrations and drying methods is satisfactory whereas the Hydranal titrations gave high values. Only the drying method was suitable for lithium sulfate.     

Simultaneous TG,DTG, DTA and EGA examination of argillaceous rock. Part II

With the new technique described in Part I of this paper, the authors investigated five Silurian shale samples and semiquantitatively determined their sulphate, sulphide, carbonate, illite and chlorite contents.

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Zusammenfassung Mittels der in Teil I beschriebenen Methoden wurden fünf Silurschiefer untersucht und deren Sulfat-, Sulfid-, Karbonat-, Illit- und Chloritgehalt halbquantitativ ermittelt.

     

Cyclodextrin assisted nanophase determination of alkaloid salts

The poor water solubility of the free base and the high dissociation constant (K_a) hinder mainly the assay of alkaloid salts. We have elaborated an enviroment friendly method that can be carried out in aqueous media. The stability difference of the cyclodextrin (CD) complexes of free and protonated bases were used for this purpose. The base is included into the hydrophobic cavity of the CD (which serves as an apolar solvent phase on molecular level) and its solubility in water is increased. Since the base forms more stable inclusion complex than its protonated species, the pK_a is decreased and the potentiometric titration is promoted by this way, too. Six different hydrohalide alkaloid salts have been investigated and the most appropriate CDs were chosen (depending on the size of the molecules and/or substituents). The results of the assays agree well with those obtained by the direct nonaqueous titrations. The stability constants of the inclusion complexes have been also computed.     

Displacement reactions in gypsum and in anhydrite

Displacement reactions between calcium sulfates (gypsum and anhydrite) and aqueous solutions of Ba⁻, Sr⁻ and Pb-salts were investigated by means of TG, DSC,microscopy and x-ray. The reactions can be followed directly by microscopy when cleavage plates of gypsum crystals are used. The first steps of crystallization are in some cases of a topotactical nature. The results presented in this paper deal mainly with the formation of barite, celestite and anglesite by displacement reactions at different temperatures.     

Reaction between carbon fibres and molten silicon: Heat determination using DTA

The highly exothermic reaction between carbon fibres and molten silicon, which is the basis of SiC-Si composite production, was investigated using a Setaram 2000 K thermoanalyser. DTA curves were recorded in 1.3 Pa vacuum and up to 1770 K, i.e. under the conditions of composite production. The results allowed calculation of the heat of the reaction, which ranged from 91 to 115 kJ/mol.     

Analytical determination of impurity anions in ionic salts using the ionizing irradiation

The new radiation method for the determination of impurity anions in insoluble oxysalts is described. The analysis includes: (1) The irradiation of salts containing impurity anions at room temperature, (2) determination of maximum concentrations of impurity paramagnetic centers formed which are close to impurity anion concentration in the range of 10⁻³ up to 10⁻¹ mole%. The method is valid for those anions whose ionization potentials are lower than the corresponding ionization potentials of the matrix.     

The instrument constant in DTA. Theory of sensing units in DTA instruments

Volume-isothermal and surface-isothermal sensing units with a gas-phase thermal barrier are described. Use of the two-point method of DTA with the surface isothermal sensing unit permits experimental determination of the internal heat resistance of the sample holder (of the reaction zone), thereby allowing elucidation of the mechanism (topochemistry) of the reaction and the finding of more exact kinetic data via a novel method of split heat capacities.

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Zusammenfassung Volumen- und oberflÄchenisotherme Me\fühler mit thermischer Gasphasenbarriere werden beschrieben. Bei Verwendung von oberflÄchenisothermen Me\fühlern kann nach der DTA-Zweipunktsmethode der innere WÄrmewiderstand bestimmt werden, wodurch die AufklÄrung des Mechanismus (Topochemie) der Reaktion und die Ermittlung genauerer kinetischer Daten über eine neue SpaltwÄrmekapazitÄts-Methode ermöglicht wird.

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