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.     

Electronic and crystalline structure of Si/SiO2 interface modified by ArF excimer laser

The native oxide layers on Si(100) surface were irradiated under UHV conditions by an ArF excimer laser pulses with energy density varied between melting and evaporating thresholds. The resulting changes were studied by LEED, AES and UPS. The increase of the energy density up to evaporation threshold results in the recrystallisation of native oxide layer. The pulses with energy densities just above the evaporation threshold ablate the top layer leaving an ordered and atomicaly clean surface. The observed (1x1) surface reconstruction is probably stabilised by strains introduced during rapid melting and quenching of the topmost layers. The surface electronic structure is dominated by random satisfaction of dangling bonds swearing a well defined surface states observed on (2x1)Si(100) surface.     

Investigations of benzimidazole derivatives

3-(1-Methyl-2-benzimidazolyl)acrylic acid was obtained by the reaction of 1,2-dimethylbenzimidazole with chloral and subsequent hydrolysis of the condensation product. The hydrochloride of the chloride of this acid and its esters and amides were synthesized. The methyl and ethyl esters of the acid were synthesized by the Wittig reaction. The IR and UV spectra of the compounds obtained are presented.See [9] for Communication XXIV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1566–1568, November, 1970.     

Determination of zinc in high purity bismuth by thermal neutron activation

A neutron activation analysis for the determination of zinc in bismuth was developed. After irradiating the samples for 44 days at 4·10¹¹n/cm²/sec, zinc was separated quantitatively by hexone extraction and precipitation as quinaldate. The sensitivity of the method was estimated as 0.05 p.p.m. No zinc could be detected in the high purity bismuth samples. An addition method of analysis showed that the precision was 1.2%.     

M?glichkeiten und Grenzen der Identifizierung von Stoffen aus ihrem Verhalten bei der isothermen Eluierungsgaschromatographie

Zusammenfassung Es wird vorgeschlagen, für die Identifizierung von Stoffen Verteilungskoeffizienten zu verwenden und diese mit Hilfe der GLC in einem einfachen Verfahren, das auch die Kontrolle der Meßbedingungen erlaubt, zu bestmimen. Dieser Vorschlag kombiniert ein relatives Meßverfahren mit der Bestimmung absoluter Größen. Der Meßgenauigkeit, die für die Identifizierung von entscheidender Bedeutung ist, wurde besondere Aufmerksamkeit gewidmet und dabei herausgestellt, daß sie im allgemeinen durch die Trennleistung der Säule begrenzt wird. Für die Auswertung der Ergebnisse bei der Verwendung von Säulen mit verschiedenen stationären Phasen wurde ein Verfahren erprobt, bei dem die an den verschiedenen Säulen gemessenen Verteilungskoeffizienten miteinander kombiniert werden. Es wurde eine Tabelle der Verteilungskoeffizienten von etwa 80 Kohlenwasserstoffen bei 50,0° C mit Squalan und Dinonylphthalat als stationären Flüssigkeiten angefertigt. An Hand dieser Tabelle wurde die Identifizierung der C₅–C₇-Kohlenwasserstoffe eines Crackproduktes durchgeführt.

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Summary It is recommended to use partition coefficients for the identification of compounds and to determine these by a simple gas-chromatographic procedure, which allows the control of the measuring conditions.This recommendation combines a relative method of measurement with the determination of absolute quantities. The accuracy of the measurement, which is decisive for the identification, was investigated and it was found that the accuracy in most cases will be limited by the resolving power of the column. For the evaluation of the results obtained with columns with different stationary phases a method was tested in which the partition coefficients measured on two different columns were combined. A table of partition coefficients of 80 hydrocarbons at 50,0° C on squalane and dinonylphthalate as stationary phases was compiled. On the basis of this table the identification of the C₅-C₇ hydrocarbons in a crack product was carried out.

     

Synthesis and Structure of the New Ammonium Indium Phosphate (NH4)In(OH)PO4

A new ammonium indium phosphate (NH₄)In(OH)PO₄ was prepared by hydrothermal reaction in the In₂O₃-NH₄H₂PO₄-NH₃/OH system (T=200°C, autogenous pressure, 7 days). The formula (NH₄)In(OH)PO₄ was determined on the basis of chemical and thermal analysis (TG/DSC), X-ray powder diffraction and IR-spectroscopy. (NH₄)In(OH)PO₄ crystallizes in the tetragonal system with space group P4₃2₁2 (No. 96); a=9.4232(1) Å, c=11.1766(1) Å, V=992.45(2) ų; Z=8. The crystal structure was refined by the Rietveld method (R_w=6.35%, R_p=5.10%). The second-harmonic generation study confirmed that structure of (NH₄)In(OH)PO₄ does not have a center of symmetry. The cis-InO₄(OH)₂ octahedra form helical chains, parallel to the c-axis. The In-O-In bonds are nearly equidistant. The chains are interconnected by phosphate tetrahedra and create tunnels containing the NH₄⁺ ions along the c-axis. (NH₄)In(OH)PO₄ is isostructural with RbIn(OH)PO₄.     

Phthalocyanines and related compounds: XXXVIII. Synthesis of symmetric taurine- and choline-substituted phthalocyanines

Procedures have been developed for the synthesis of a series of metal complexes derived from water-soluble anionic and cationic octa-4,5-carboxyphthalocyanine-taurine and choline conjugates.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1907–1911.Original Russian Text Copyright © 2004 by Mikhalenko, Soloveva, Lukyanets.For communication XXXVII, see [1].This revised version was published online in April 2005 with a corrected cover date.     

Quantitative estimation of the α-effect in the reactions yielding phosphorus-containing thiosemicarbazides

The α-effect in the reactions of O,O-diaryl phosphorohydrazidothioates with phenyl isothiocyanate in benzene at 25°C was quantitatively evaluated from the kinetic data. The probable reaction mechanism was suggested, and the causes of the α-effect in these reactions are discussed. An approximate linear correlation is observed between the α-effect in the reactions of O,O-diaryl phosphorohydrazidothioates with phenyl isothiocyanate, basicity constants of the hydrazides, and σ^p constants of the substituents at the P atom. The value of the α-effect is largely determined by the structure of the transition state.     

Mechanism and kinetics of CO hydrogenation on metals

An antibatic relation has been established between the catalytic activities r of metals in relation to hydrogenation of CO and the selectivity in relation to methane . A mechanism is proposed for the reaction which makes it possible to interpret the observed kinetic relationships, the sequences of activities and selectivities, and also the relation between r and .Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 549–553, September–October, 1985.     

Isoscalar factors for tetragonal,orthorhombic, monoclinic and triclinic shubnikov point groups

The relations between isoscalar factors for corepresentations of antiunitary magnetic point groups are discussed in the case of associated corepresentations. The tables of the isoscalar factors for the single- and double-valued corepresentations of all tetragonal, orthorhombic, monoclinic, and triclinic Shubnikov point groups are given. Some peculiarities of the calculation method of the isoscalar factors for corepresentations are considered.