Potentiometric studies of dithiooxamide with a sulphide-selective membrane electrode

The sulphide-selective electrode is applicable to the determination of dithiooxamide by titration with silver nitrate. The effect of the alkali content of the solutions on the reaction has been studied. The reaction products are silver sulphide, oxalic acid, and nitric acid. If the alkali concentration of the solution is lower than that equivalent to the acid formed during the titration, the amount of sulphide produced by hydrolysis decreases and the equilibrium potential is established more slowly.The determination is rapid and accurate in the presence of 1 M sodium hydroxide.     

Interaction of adenine and thymine with aqueous sugar solutions

The solubility of the nucleic acid bases, adenine and thymine, in aqueous erythritol, xylose, glucose, and sucrose solutions has been studied. The solubility of adenine increases linearly with glucose and sucrose concentration, whereas with the other reagents a nonlinear increase is observed. Below 1.5M reagent concentration, the solubility of adenine increases in the order erythritol < robose, xylose < glucose < sucrose. The solubility of thymine in these solutions, on the other hand, decreases, increases, or does not change depending upon the reagent. The effect of temperature on the solubility of adenine and thymine in sugar solution indicates that the transfer of these molecules from water to sugar solution is exothermic.Presented in part at the VIIth All-India Symposium in Biophysics held at Visva Bharati University during October 1976.     

Adsorption Peculiarities of Carbon Monoxide on Iridium Electrodeposits

The transients of current and open-circuit potential observed at CO adsorption on Ir/Pt electrodes in solutions of sulfuric and hydrochloric acids are shown to adequately agree with those theoretically expected. From voltammetric curves of electrooxidation of chemisorbed CO, the values of its adsorption are estimated by making a proper double-layer correction. It is concluded that CO is preferentially adsorbed in the bridge form. During CO adsorption from sulfuric acid solutions on an electrode with a preliminarily accumulated monolayer of copper adatoms (Cu_ad), small negative current are observed and Cu_ad are displaced by 50%. To explain these results, it is assumed that CO is reduced by copper adatoms.     

Atomic Absorption Assay of Noble Metals in Ores with the Use of Sample Decomposition by Ultrasound

An atomic absorption assay of gold, silver, and palladium in various types of ores is performed with the use of ultrasound at the fire assay stage. It is shown that ultrasound can reduce the temperature and duration of fusion and increase the recovery of noble metals into the lead button.     

Organic synthesis on the microgram scale. V

Summary This paper describes a method for theg synthesis of flavone acetates in a sealed capillary tube. The reaction products are separated and purified on a thin-layer plate. The esters are then hydrolyzed on the plate and the parent flavones regenerated. A simple heating device is used which allows for observation of the reaction.

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Zusammenfassung Beschreibung der Mikrogrammsynthese von Flavonacetaten in einem verschmolzenen Kapillarröhrchen. Die Reaktionsprodukte werden auf einer Dünnschichtplatte getrennt und gereinigt. Dann verseift man die Ester auf der Platte und stellt die freien Flavone dar. Ein einfaches Heizgerät ermöglicht die Beobachtung der Reaktion.

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For part IV of this series see Mikrochim. Acta [Wien]1969, 352.     

A family of multiderivative methods for the numerical solution of the Schrödinger equation

A family of multiderivative methods with minimal phase-lag are introduced in this paper, for the numerical solution of the Schrödinger equation. The methods are called multiderivative since uses derivatives of order two, four or six. Numerical application of the new obtained methods to the Schrödinger equation shows their efficiency compared with other similar well known methods of the literature.Active Member of the European Academy of Sciences and Arts     

Continuous flow thin layer headspace (TLHS) analysis

Summary The paper presents a new method of a continuous isolation and determination of volatile organic halogens (VOX) in drinking waters based on so-called thin layer headspace (TLHS) isolation technique. The liberated volatile compounds are mineralized in an empty quartz tube at 850°C and absorbed in a buffered washing solution. After separation of air the halogen ions are determined potentiometrically in a flow-through cell using a silver/silver choride indicating electrode. The potential of the electrode is a linear function of the halogen ion concentration in the washing solution within the VOX concentration range usually encountered in drinking waters. The estimated detection limit of the method is ca. 0.1 g/l VOX and can be further improved by increasing the concentration factor. The theory of the TLHS isolation method has been further developed and verified. The derived dependences enable a simultaneous determination of the effective partition coefficients in the system, thus enabling calculation of the optimal gas flow rate.Part I and II, see [1, 2]     

Analytical aspects of some organic acids

Summary A direct titrimetric method for the estimation of iron(III) has been developed, which involves the adjustment of concentration of iron(III) andPh, dilution, addition of 1 ml of 2% indicator solution and titration with EDTA (30° to 35° C). It is based on the fact that the iron(III) forms a blue coloured complex which is destroyed at the 11 molar ratio making the end-point of the titration. Quantity of iron(III) as small as 23.2 mg can be titrated accurately when present in a volume of 100 ml. Study of interferences revealed that quite a number of elements like Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, UO₂ ²⁺ and Mn²⁺ does not interfere, whereas much interference is caused by Cu²⁺, Zn²⁺, Pb²⁺, Fe²⁺, Co²⁺, Ni²⁺, ZrO²⁺, V0²⁺, Al³⁺, Cr³⁺, Ti⁴⁺, Ce⁴⁺ and Th⁴⁺. The method proposed for iron(III) is selective and should be of considerable use in many cases.Part III: See Z. analyt. Chem. 167, 332 (1959).     

Wannier-Stark effect on surface states

A recursive Green-function (RGF) technique is used to study the surface states of an electrified solid. The concatenating nature of the method leads to a continued-fraction form of the RGF, which can be expressed as a ratio of Bessel functions. The surface density of states (SDOS), derived from the RGF, reveals a quasi-Stark-ladder distribution of the energy levels at the surface atom. The dependence of the SDOS on the applied field and surface perturbation parameters is discussed.     

Phosphinofenchol or metastable phosphorane? Phosphorus derivatives of fenchol

Not the expected phosphinofenchol 1 but phosphorane 2 is obtained after reaction of 2-lithio(diphenylphosphino)benzene with (-)-fenchone. Surprisingly, ONIOM(B3LYP/6-31G*:UFF) computations of 1 and 2 as well as B3LYP analyses of smaller model systems point to a lower thermodynamic stability of phosphoranes relative to their isomeric alkoxyphosphines. An analogue inherent instability is computed for the methylphosphorane 10, which is also synthesized and characterized by X-ray analysis. Decreasing ring size in cyclic phosphoranes, that is, from five- to four-membered ring systems, destabilizes cyclic phosphoranes even more. This computational prediction is verified experimentally by reaction of lithiomethyl(diphenylphosphine) with (-)-fenchone and subsequent isolation of the corresponding phosphinofenchol. Protonation or alkylation of phosphoranide intermediates can account for the formation of metastable phosphoranes.