Synchronization of signal sampling with liquid pulsation in systems with peristaltic pumps

Method and electronic circuitry are described for synchronization of analytical signal sampling with pulsation of liquid flow in systems with a peristaltic pump. The technique is illustrated for cathodic stripping voltammetry of manganese.     

Acidity and activity of H-mordenite in m-xylene isomerization

The dependence of the activity of H-mordenites prepared from a natural mordenite on the nature and strength of the acid groups present was studied. The superior catalytic activity and stability of the H(Ag)–MOR zeolite compared with other H-forms is explained on the basis of NH₃ adsorption and IR measurements.

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H-, . H(Ag)–MOP H- NH₃ .

     

Maßanalytische Bestimmung von Merkapto-Benzthiazol im Wärmeaustauscher eines Reaktors

Zusammenfassung Eine volumetrische Methode zur Bestimmung geringer Mengen Merkapto-Benzthiazol in der Kühlflüssigkeit von Reaktoren wurde ausgearbeitet. Es wird in ammoniakalischem Medium mit ammoniakalisehem Silbernitrat titriert. Das Merkapto-Benzthiazol bildet mit Silberionen einen weißen, flockigen Niederschlag. Der Endpunkt der Titration wird mit Hilfe der Dead-stop-Indikation bestimmt. Er wird durch eine sprunghafte Stromstärkeerhöhung (Pt-Pt-Elektrode, 500 mV und 10^–7 A Empfindlichkeit des Galvanometers) angezeigt. Die Methode wird durch Triäthanolamin, Glykol, geringe Mengen von Chlorid und Phosphat nicht gestört.

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Summary A volumetric method has been developed for determining slight amounts of mercapto-benzthiazol in the cooling liquid of reactors. It is titrated in ammoniacal medium with ammoniacal silver nitrate. The mercapto-benzthiazol yields a colorless flocculent precipitate with silver ions. The endpoint of the titration is found by the dead stop indication. It is signalled by a sudden jump in the current strength (Pt-Pt-electrode, 500 mV and 10^–7 amp sensitivity of the galvanometer). The method is not impaired by triethanolamine, glycol, slight amounts of chloride, nor by phosphate.

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Résumé On a mis au point une méthode volumétrique pour le dosage de faibles quantités de mercaptobenzothiazole dans le liquide de refroidissement des réacteurs. On titre en milieu ammoniacal par le nitrate d'argent ammoniacal. Le mercaptobenzothiazole forme un précipité blanc, floconneux avec les ions argent. On détermine le point d'équivalence du titrage par la méthode du «dead stop end point». Il se trouve signalé par une augmentation brusque de l'intensité (électrodes Pt-Pt, 500 mv et 10^–7 A de sensibilité du galvanomètre). La triéthanolamine, le glycol, de petites quantités de chlorures et de phosphates, ne gênent pas.

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Vorgetragen beim Symposium für analytische Chemie in Graz, 29. September bis 1. Oktober 1965.     

Pattern of separatrices and intrinsic reaction coordinates for degenerate thermal rearrangements

A structurally stable model of the standard adiabatic gradient field of the potential energy surface for certain pericyclic reactions is derived.These reactions are not subjected to the principles of orbital isomerism or to the Woodward-Hoffmann rules.Use is made of a principle established by Ariel Fernández and Oktay Sinanolu which precludes direct meta-IRC connections between transition states.It is shown that Jahn-Teller isomers of the singlet biradicals involved in the process are not interconvertible since the biradical configuration is not a transition state but a critical point with Hessian matrix with two negative eigenvalues.The topological features of the PES obtained by combinatorial methods are in full agreement with earlier results obtained from MINDO calculations.     

Derivatives of carbohydrazide,thiocarbohydrazide and diaminoguanidine as photometric analytical reagents. III

Summary An absorption method for the collection of acid and condensable volcanic gases is described. A Cd(OH)₂ suspension allows the simultaneous sampling of sulfide and sulfur dioxide. A complete scheme for chemical analysis of H₂O, CO₂, H₂S, SO₂, HCl and HF is presented.The method is relatively simple and accurate and requires only simple equipment. Moreover, separate samples of the condensable part of the volcanic gas may be used for analysis of trace elements.

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Probenahme und Analyse vulkanischer Gase

Zusammenfassung Eine Absorptionsmethode zur Probenahme saurer und kondensierbarer Vulkangase wurde beschrieben. Eine Cd(OH)₂-Suspension ermöglicht die gleichzeitige Probenahme von H₂S und SO₂. Ein Analysenschema für die chemische Analyse von H₂O, CO₂, H₂S, SO₂, HCl und HF wurde angegeben. Das Verfahren ist relativ einfach und genau; es erfordert nur eine einfache Ausrüstung. Proben des kondensierbaren Anteils der Gase dienen zur Bestimmung der Spurenanteile.

     

On-line coupling of supercritical fluid extraction with high-performance liquid chromatography for the determination of explosives in vapour phases

An investigation into the selectivity of an iminodiacetic acid (IDA) modified silica gel column for transition and heavy metal ions using non-chelating inorganic eluents has been carried out. A number of eluent parameters were investigated to determine the exact retention mechanism taking place and to control selectivity. The parameters studied were eluent ionic strength and the nature of the inorganic salt used, eluent pH and eluent temperature. The results obtained showed how despite certain metal ions exhibiting similar stability constants with the bonded IDA groups, careful control of each of the above parameters, in particular eluent chloride ion concentration and eluent temperature, could result in large changes in selectivity. Optimal conditions for the isocratic and gradient separation of Mg(II), Ca(II), Mn(II), Cd(II), Co(II), Zn(II) and Pb(II) were determined. An isocratic method using a 0.035 M KCl, 0.065 M KNO3 (pH 2.5) eluent was successfully applied to the determination of Mn(II), Cd(II), Co(II) and Zn(II) at concentrations between 20 and 121 microg/l in a freshwater certified reference material (NIST 1640).     

Kinetik der Entstehung des Zinktartrats

Zusammenfassung Aus potentiometrischen Daten wurde die Konstante der Entstehungsgeschwindigkeit des Zinktartrates bei 18° berechnet. Ihr durchschnittlicher Wert beträgt 1,3·10² mol·min^–1 und der Wert der Zerfallsgeschwindigkeitskonstante beläuft sich im Durchschnitt auf 7,5·10^–2 mol·min^–1.     

Effect of selenium oxidation state on cadmium translocation in chamomile plants

Syntheses and spectral characteristics of cadmium(II) compounds (CdSeO₄, CdSeO₃, and Cd(NCSe)₂(nia)₂) containing selenium in oxidation states (VI), (IV), and (-II) are described. In Cd(NCSe)₂(nia)₂, nicotinamide (nia) and selenocyanate anions are bonded to Cd atom as N-donor monodentate ligands. Nicotinamide is coordinated through the ring nitrogen atom. The effects of these selenium compounds as well as Cd(NCS)₂(nia)₂ on the growth and Cd accumulation in roots and shoots of hydroponically cultivated chamomile plants (cultivar Lutea) were studied. In the applied concentration range (12–60 μmol dm⁻³) Cd(NCS)₂(nia)₂ affected neither the length nor the dry mass of roots and shoots. Other compounds applied at 24 μmol dm⁻³ and 60 μmol dm⁻³ significantly reduced dry mass of roots and shoots. Selenium oxidation state in the cadmium compounds affected Cd accumulation in plant organs as well as Cd translocation within the plants, which was reflected in the values of bioaccumulation (BAF) and translocation factors (S/R). Cd amount accumulated by shoots was lower than that in the roots. The highest BAF values determined for Cd accumulation in shoots were obtained with CdSeO₄. Substitution of S with Se in the Cd(NCX)₂(nia)₂ (X = Se or S) caused an increase of Cd translocation into the shoots. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Structural characterization of CeO(2)-ZrO(2)/TiO(2) and V(2)O(5)/CeO(2)-ZrO(2)/TiO(2) mixed oxide catalysts by XRD, Raman spectroscopy, HREM, and other techniques

Structural characteristics of CeO(2)-ZrO(2)/TiO(2) (CZ/T) and V(2)O(5)/CeO(2)-ZrO(2)/TiO(2) (V/CZ/T) mixed oxide catalysts have been investigated using X-ray diffraction (XRD), BET surface area, Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HREM) techniques. The CeO(2)-ZrO(2) (1:1 mole ratio) solid solution was deposited over a finely powdered TiO(2) support by a deposition precipitation method. A nominal 5 wt % V(2)O(5) was impregnated over the calcined (773 K) CZ/T mixed oxide carrier by a wet impregnation technique. The obtained CZ/T and V/CZ/T samples were further subjected to thermal treatments from 773 to 1073 K to understand the dispersion and temperature stability of these materials. In the case of CZ/T samples, the XRD results suggest the formation of different cubic and tetragonal Ce-Zr-oxide phases, Ce(0.75)Zr(0.25)O(2), Ce(0.6)Zr(0.4)O(2), Ce(0.5)Zr(0.5)O(2), and Ce(0.16)Zr(0.84)O(2) in varying proportions depending on the treatment temperature. With increasing calcination temperature from 773 to 1073 K, the intensity of the lines pertaining to cubic Ce(0.6)Zr(0.4)O(2) and Ce(0.5)Zr(0.5)O(2) phases increased at the expense of cubic Ce(0.75)Zr(0.25)O(2), indicating more incorporation of zirconia into the ceria lattice. The TiO(2) was mainly in the anatase form whose crystallite size also increased with increasing treatment temperature. A better crystallization and more incorporation of zirconia into the ceria lattice was noted when CZ/T was impregnated with V(2)O(5). However, no crystalline V(2)O(5) could be seen from both XRD and RS measurements. In particular, a preferential formation of CeVO(4) compound and an intense tetragonal Ce(0.16)Zr(0.84)O(2) phase were noted beyond 873 K. The HREM results indicate, in the case of CZ/T samples, a well-dispersed Ce-Zr-oxide of the size approximately 5 nm over the bigger crystals ( approximately 40 nm) of TiO(2) when treated at 873 K. The exact structural features of these crystals as determined by digital diffraction analysis of experimental images reveal that the Ce-Zr-oxides are mainly in the cubic fluorite geometry and the TiO(2) is in anatase form. A better crystallization of Ce-Zr-oxides ( approximately 8 nm) over the surface of bigger crystals of TiO(2) was noted at 1073 K. A further enhancement in the crystallite size and zirconia-rich tetragonal phase was noted in the case of V/CZ/T samples. Further, the structure of CeVO(4) formed was also clearly identified in conformity with XRD and RS results.     

Extraction distribution of microamounts of cesium in the two-phase water-HCl-nitrobenzene-dibenzo-18-crown-6-hydrogen dicarbollylcobaltate system

Summary Extraction distribution of microamounts of cesium in the water-HCl-nitrobenzene-dibenzo-18-crown-6(L)-hydrogen dicarbollylcobaltate has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺, CsL⁺and CsL_2,⁺are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.