Determination of pentachlorophenol residues in wine and corks by solvent extraction methodology and specific gas chromatography detection

Summary A gas chromatographic methodology with selective detection is presented for the analysis in wines and corks of pentachlorophenol residues, which are suspected to be the most likely precursors of some off-flavours described in several wine samples. After derivatisation, pentachlorophenol acetate residues were monitored by electrolytic conductivity detection and/or mass spectrometric detection in the selective ion mode at m/z 264 and 266. Recoveries varied from 80 to 96% for wine samples fortified with 5 to 100 g l^–1 and from 83 to 91% for corks (fortified at 25 to 100 g kg^–1). The proposed methodology allowed for a determination limit of g l^–1 for wine and 10 g kg^–1 for corks.     

Diacetylenic Derivatives of Fe2(CO)6(μ-EE′): Spectroscopic Investigations of Fe2(CO)6{μ-EC(H) = C(C≡ CMe)E′} (E = E′, E ≠ E′; E, E′ = S, Se, Te)

The diacetylenic adducts, Fe₂(CO)₆{-EC(H) = C(C CMe)E} (E = E, E E; E, E = S, Se, Te) (1–8) have been obtained from the room temperature stirring of Fe₂(CO)₆(-EE) with HC CC CMe in methanol solvent containing sodium acetate. Compounds 1–8 have been characterized by IR and multinuclear NMR (¹H, ¹³C, ⁷⁷Se, and ^l25Te) spectroscopy. Trends in the chemical shifts of ⁷⁷Se and ¹²⁵Te NMR spectra of Fe₂(CO)₆{-EC(H) = C(C CMe)E} with a variation of EE are discussed.     

Determination of nitrate in natural waters by flow-injection analysis

Summary Nitrate was determined in natural water samples by flow-injection spectrophotometry. It was reduced to nitrite with copperized cadmium and the nitrite thus produced reacted with p-aminoacetophenone and m-phenylenediamine. The limit of detection was about 1.5 g l^–1 for sample injections of 650 l. The sampling rate was about 40 samples h^–1 and the relative standard deviation was above 1% for 0.1–0.3 mg l^–1 nitratenitrogen. Nitrite present in the sample was determined separately and subtracted.

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Nitratbestimmung in natürlichen Wässern mit Hilfe der Fließinjektions-Analyse

Zusammenfassung Nitrat wird bei dieser Methode mit Hilfe einer Cu/Cd-Reduktionssäule zu Nitrit reduziert, das mit p-Aminoacetophenon und m-Phenylendiamin zur Reaktion gebracht wird. Die gebildete Verbindung wird spektral-photometrisch gemessen. Die Nachweisgrenze beträgt etwa 1,5 g/l bei injizierten Probevolumina von 650 l. Der Probendurchsatz beträgt 40/h. Die relative Standardabweichung liegt über 1% bei 0,1–0,3 mg/l Nitrat-Stickstoff. Vorhandenes Nitrit wird gesondert bestimmt und abgezogen.

     

Kinetic analysis of thermogravimetric data. XI thermal decomposition of some metal dithionates

A thermal analytical study of Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba and Zn dithionates is reported. The decomposition of the dithionate ion is endothermic in the case of the Na, K, Rb, Cs and NH₄ salts, but exothermic with Li, Mg, Sr, Ba and Zn. Kinetic parameters have been derived from the TG curves by means of the Coats-Redfern method. The validity of a linear kinetic compensation law is reported for the loss of crystal water and separately for the decomposition of the dithionate ion.

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Zusammenfassung Es wird über eine thermoanalytische Untersuchung der Dithionate von Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba und Zn berichtet. Die Zersetzung des DithionatIons ist im Falle von Na, K, Rb, Cs und NH₄-Salzen endotherm, im Falle von Li, Mg, Sr, Ba und Zn hingegen exotherm. Die kinetischen Parameter wurden aus den TG-Kurven mittels der Coats-Redfern-Methode abgeleitet. Es wird über die Gültigkeit eines linearen kinetischen Kompensationsgesetzes für den Verlust von Kristallwasser berichtet und gesondert für die Zersetzung des Dithionat-Ions.

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Résumé On présente les résultats d'une étude par analyse thermique des dithionates de Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba et Zn. La décomposition est endothermique dans le cas des sels de Na, K, Rb, Cs et ammonium tandis qu'elle est exothermique dans le cas des sels de Li, Mg, Sr, Ba et Zn. Les paramètres cinétiques sont déduits des courbes TG par la méthode de Coats-Redfern. La validité d'une loi de compensation cinétique linéaire est étudiée pour la perte de l'eau d'hydratation ainsi que pour la décomposition de l'ion dithionate.

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Li, Na, K, Rb, Cs,. NH₄, Mg, Ca, Sr, Ba Zn. [ Na, K, Rb, Cs NH₄ , Li, Mg, Sr, Ba Zn . - . .

     

Effect of carbon support on the hydrogen sorption of platinum

The hydrogen sorption of carbon-supported platinum catalysts, studied by the potentiodynamic method, differs significantly from that of unsupported platinum. The difference depends on the preparation method and on the nature of the support. Possible explanations are suggested as (i) some kind of interaction between metal and support atoms during impregnation, (ii) high dispersity (amorphous structure) and (iii) hydrogen spillover onto the carbon support.

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Pt/C, . . (I) , (II) ( ), (III) .

     

Monolayer vanadia on titania systems from alkoxide precursors. Part III. Activity in secondary alcohol oxidation

The activity of V⁵⁺ ion monolayer supported on anatase, rutile, and anatase-rutile mixed carrier and of bulk V₂O₅ was examined in isopropyl alcohol and cyclohexanol oxidation. Catalysts exhibited remarkable activity in ketone formation. At higher temperatures benzene was the predominant product of cyclohexanol reaction.

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V⁵⁺, , - V₂O₅, . . .

     

Chemical behaviour of helium muonide just after muon catalyzed fusion

Chemical behaviour of a helium muonide atom /He^o/ can be understood on the analogy of its hydrogen homologues, muonium /Mu/, deuterium /D^o/ and tritium /T^o/. In muon catalyzed fusion /CF/, a small fraction of negative muon in the fusion cycle sticks to helium to give proton-like He⁺ which easily picks up one electron forming He^o. The energy of He⁺ at birth is about 3.5 MeV being in a similar situation to the case of a hot tritium atom produced by /n, p/ or /n, / reaction. The reaction cross section and rate of He^o reactions are estimated.     

Mono and dinuclear cationic rhodium(I) and iridium(I) complexes with sulphur donor and group Vb ligands

Summary Rhodium(I) and iridium(I) mixed complexes of the formulae [M(diolefin)LL]ClO₄, [M(diolefin)L₂L]ClO₄, [(diolefin)LIr(-L)₂IrL(diolefin)](ClO₄)₂, [(diolefin)LM(-L-L)ML'(diolefin)](ClO₄)₂, [(diolefin)Rh{-(L-L)}₂Rh(PPh₃)₂](ClO₄)₂ and [(diolefin)LIr{-(L-L)}₂IrL (diolefin)](C1O₄)₂, (L=monodentate sulphur ligand, L-L=bidentate sulphur ligand, L=group Vb ligand; M=Rh, diolefin=1,5-cyclooctadiene (COD) or 2,5-norbornadiene (NBD); M=Ir, diolefin=COD) are described.Author to whom all correspondence should be directed.     

Luminescence of the pyrene/N,N-diethylaniline triplet exciplex in methanol at room temperature

Fluorescence, whose spectral and magnetic properties permit its assignment to the luminescence of a triplex exciplex, has been discovered at times 3 sec after photoexcitation in the luminescence spectrum of the pyrene+N,N-diethylaniline system in methanol at 600 nm by the method of nanosecond stroboscopic fluorometry.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 25, No. 5, pp. 623–626, September–October, 1989.     

Solution structures and dynamic behaviour of some iron chalcogen derivatives

Summary ¹³C-n.m.r. spectra of (-SR)₂Fe₂(CO)₆, (-SR)₂Fe₂(CO)₅P(n-Bu)₃ and (-X)₂Fe₂(CO)₆ (X=S or Se) show that the solid state structure is maintained in solution. N.m.r. evidence indicates that two isomeric species, not separable by means of the usual physicochemical methods, are present for (-SPh)₂Fe₂(CO)₆ with an overwhelming predominance of theanti form. The phosphine substitutes a COtrans to the iron-iron bond. For any of the iron chalcogen derivatives examined, variable temperature¹³C-n.m.r. spectra show that carbonyl exchange occur in one step. The energy barrier for the exchange of carbon monoxide in the phosphine derivative is lower than that in the unsubstituted complex.