Polarographic determination of pilocarpine using the catalysed pre-wave of nickel(II)

On the basis of a detailed study of the pilocarpine-induced nickel(II) pre-wave using various polarographic techniques, an electrode process mechanism is proposed in which the formation of a catalytic complex between aquo-nickel(II) and veronalate-nickel(II) on the one hand and unprotonated pilocarpine adsorbed on the electrode surface on the other is followed by the reduction of nickel(II) in the complex and the release of the catalytic ligand. The pre-peak recorded by differential-pulse polarography in the system 1 × 10^?3 M Ni(II)-1 × 10^?2 M sodium veronal, nitric acid (pH 8.5) (with ionic strength maintained at 0.2 with sodium nitrate) can be used for quantitative determination of pilocarpine at concentrations in the range 2.5 × 10^?7-8 × 10^?6 M.     

Study of the microstructure of tetrahydrofuran-3,3 dimethyloxetane copolymers by 13C-NMR spectroscopy.

The microstructure of tetrahydrofuran (A)-3,3 dimethyloxetane (B) copolymers was studied by ¹³C-{¹H}-NMR spectroscopy. Only the methyl carbons corresponding to the 3,3 dimethyloxetane unit appear as a singlet, whereas the other carbons present a more complicated spectral pattern than it would be expected if ? effects were negligible. The assignment of the resonance signals allowed the determination of the values of the probabilities of the different triads, which were in good agreement with those obtained from the reactivity ratios.     

Solubility product relations in the rare earth hydrous hydroxides

The solubility products for some rare earth hydroxides and their temperature dependence have been shown. Greater solubility is shown for larger atomic radii and for lower temperature.     

Electroviscous Effect in Dilute Suspensions of Alumina

A study on the electroviscous effect of alumina suspensions has been made. At the low volume fraction of the particles studied here only a first-order effect was detected. Ubbelohde-type capillary viscometers have been used. A simple method to determine the hydrodynamic constant k(1) has been proposed. The experimental primary electroviscous coefficients corresponding to different electrolyte concentrations have been compared with two different theoretical approachs (I. G. Watterson, and L. R. White, J. Chem. Soc. Faraday Trans. 2 77, 1115 (1981); F. J. Rubio-Hernández, E. Ruiz-Reina, and A. I. Gómez-Merino, J. Colloid Interface Sci. 206, 334 (1998)) and the results suggest that the presence of a dynamic Stern layer plays a certain role in this effect. Copyright 2000 Academic Press.     

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.     

HPLC-Electrochemical detection with graphite-poly (tetrafluoroethylene) electrode Determination of the fungicides thiram and disulfiram

The suitability of composite graphite-poly(tetrafluoroethylene) (Teflon) electrodes as amperometric indicator electrodes in HPLC detection is demonstrated. The determination of the fungicides thiram and disulfiram in the presence of ziram has been chosen as an analytical problem. The optimization of working conditions, such as the choice of the organic solvent used in the mobile phase as well as its percentage, the potential applied to the composite electrode, and the time elapsed between mixing the carbamates and the injection, has been accomplished by using the wall-jet flow-cell configuration. The effect of the acetonitrile percentage used in the mobile phase on the retention of thiram, disulfiram, ziram and phenol was evaluated. Resolution up to the baseline can be achieved with 45% acetonitrile. The sensitivity of the determination of thiram and disulfiram in the presence of a constant concentration of ziram is slightly better when using a wall-jet cell; however, the background current is higher, as well as the baseline noise and the time necessary to achieve stabilization of the baseline before the injection. Lower limits of detection for both fungicides, as well as a better repeatability, were obtained when using a thin-layer flow cell configuration. As an application, the determination of thiram in spiked apple samples, at a level of 0.5 mg thiram kg(-1) apple, has been carried out with a mean recovery of 97 +/- 3% for a significance level of 0.05.     

Über Reaktionen von Nitrosophenolen, 4. Mitt.: Reaktion von Nitrosonaphtholen mit Naphtholen

Zusammenfassung Die Reaktion von 1-Nitroso-2-naphthol mit 1-und 2-Naphthol sowie die Reaktion von 2-Nitroso-1-naphthol mit 2-Naphthol in Äthanol und in Äther bei Anwesenheit von HNO₃ gibt 5H-Dibenzo[a,j]phenoxazon-(5) (I), 5H-Dibenzo[a,j]phenoxazon-(5)-14-oxid (II), 5H-Dibenzo[a,h]phenoxazon-(5) (III) sowie 5H-Dibenzo[a,h]phenoxazon-(5)-14-oxid (IV). Es wurde ein Reaktionsmechanismus vorgeschlagen und die Konstitution der hergestellten Verbindungen spektrophotometrisch und potentiometrisch bestimmt.

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The reaction of 1-nitroso-2-naphthol with 2-and 2-naphthol and the reaction of 2-nitroso-1-naphthol with 2-naphthol in ethanol or ether in the presence of nitric acid have been studied. The main reaction products isolated were the dibenzophenoxazones I–IV. The reaction mechanism for their formation is proposed.

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Mit 4 Abbildungen     

The effect of mechanical activation on the thermal decomposition of chalcopyrite

Experimental results on the influence of preliminary mechanical activation on the thermal decomposition of chalcopyrite are presented and discussed. The following experimental facts were found: