Effect of plasmatron excitation conditions on the determination of traces

Optimal analysis conditions can be selected and errors caused by variations in the excitation conditions can be decreased or corrected based on the results of studying the temperature distribution along the plasma torch height and correlations between the analytical signal Y and the correcting signal Z that follows the temperature variation in the plasma torch. The obtained correlations can be used to create automated feedback between the spectrum recording system and the mode control system of the plasmatron.     

Chromatographic studies of corrosion sites in metallic materials

Many types of corrosion phenomena are controlled by the ionic composition of a small volume of solution at the surface. Localized corrosion and atmospheric corrosion are two examples in which < 1 μl of solution can cause dramatic damage. Ion chromatographic (IC) techniques have been used to analyze these solutions in order to gain a better understanding of the mechanisms which govern them. Two examples are presented. The presence of minor alloying elements at localized corrosion sites in two aluminum alloys has been demonstrated, indicating non-stoichiometric dissolution of the alloy during localized corrosion. In addition, IC analysis allowed the determination of the species responsible for the atmospheric corrosion failure of electrical connectors, including their likely origin.     

Synthesis and properties of enamines of the phenanthridine series

We have synthesized secondary and tertiary enamines, derivatives of 1,2,3,4,4a,5,6,10b-octahydrophenanthridine, and we have considered the Z,E-isomerism of the enaminoesters.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1374–1377, October, 1993.     

Kinetic study of the metalation of a polystyrene model compound by the secondary butyllithium-N,N,N′,N′-tetramethylethylene diamine complex

2.5-Diphenyl hexane, a model compound of polystyrene was metalated by a complex of secondary butyllithium and N,N,N′,N′-tetramethylethylene diamine in heptane. At various times, the lithiated dimer was quenched with deuterated methanol. The deuterated compound was examined by mass spectrometry and from the deuterium content, the degree of lithiation was determined. The effects of the concentration of styrene units, secondary butyllithium and diamine on the lithiation were studied at 20 C and ?20 C. The overall rate of metalation was first order with respect to the styrene units concentration and half-order with respect to sec. butylithium-TMEDA complex concentration. The kinetic results were explained by the presence at 20 C of the 1 4 complex (1 sec. BuLi 4 TMEDA) and at ?20 C of the 1–2 complex (1 sec. BuLi 2 TMEDA).     

Isolation and separation of transplutonium and rare-earth elements in unusual oxidation states on ion exchangers in inorganic acid solutions

The behaviour of transplutonium and rare-earth elements on anion and cation exchangers in solutions of H₃PO₄ and H₂SO₄ in the presence of oxidants (KBrO₃, PbO₂, (NH₄)₂S₂O₈) and in HCl solutions in the presence of reducing agents [Zn(Hg), Eu²⁺] depending on acid concentration as well as on oxidant content and nature in solution or in resin and other factors has been studied. Effective methods of Bk(IV), Ce(IV), Am(VI), Eu(II) and Md(II) separation from trivalent TPE and REE, as well as continuous methods of isolation of isotopically pure radionuclides²⁵⁰Bk,¹⁴⁴Pr by using ion exchangers and inorganic acid solutions have been developed.     

High-performance size-exclusion chromatographic determination of the potency of biosynthetic human growth hormone products

A new high-performance size-exclusion chromatography method has been developed for the determination of potency of human growth hormone products. This method has been extensively validated and shown to correlate well with the hypophysectomized rat bioassay which has been used traditionally. The method is much more precise than the traditional bioassay and thus provides more reliable means of producing consistent biosynthetic human growth hormone batches.     

9-Alkylideneazafluorenes

A number of tertiary aza-9-fluorenols were obtained from 4- and 2-azafluofenones and were subjected to dehydration in order to synthesize the previously unknown 9-methyleneazafluorenes. The corresponding 9-methyleneazafluorenes and their polymers were obtained simultaneously in relatively stable form from both pyridine-ring-substituted and -unsubstituted 4-aza-9-fluorenols and from 1,3-diphenyl-2-aza-9-fluorenol. On the basis of an analysis of the mass spectrum of the polymer obtained from 9-methylene-4-azafluorene it was concluded that it is evidently isolated in the form of two dimers — dispiro [bis (4-aza-9-fluorene)-1, 3-cyclobutane] and the analogous product of dispiro addition with a 1,2-substituted cyclobutane ring. Condensation of the corresponding azafluorenes with benzaldehyde gave their 9-benzylidene derivatives in the form of geometrical isomers, the structures of which were established on the basis of the PMR spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1234–1240, September, 1978.     

Anwendung der Streustrahl-Methode zur Bestimmung der Elemente in Mineral?lprodukten mit Hilfe der R?ntgenfluorescenz-Spektral-Analyse am Beispiel der Bleibestimmung in Ottokraftstoffen

Zusammenfassung In einem relativ einfach durchzuführenden Verbundverfahren wird Selen im Sauerstoff-strom innerhalb 15 min bei 1100–1150°C quantitativ aus den Metall- bzw. Metalloxidschmelzen verdampft und in einer mit flüssigem Stickstoff gekühlten Vorlage aufgefangen. Das aus der Vorlage mit einer definierten Menge verdünnter HNO₃ in Gegenwart von Ni-Nitrat gelöste Selen läßt sich direkt durch AAS mit dem Graphitofen (FAAS) äußerst nachweisstark und zuverlässig bestimmen. Die Nachweisgrenze (elektrodenlose Entladungslampe) liegt bei 3×10^–11 g Se. Der Verfahrensverbund erlaubt mit Probenmengen 10 g in Ag und Au Se-Gehalte 0,05 ppb,inCu 0,1 ppb,in Bi 0,2 ppb und in Pb 10 ppb zu erfassen. Für draht-, stab- und spanförmige Proben erhält man für Se-Gehalte von 2–0,002 ppm Variationskoeffizienten zwischen 3 und 6%. Die Vollständigkeit der Se-Verdampfung aus den Matrices Cu, Ag, Au und Bi wurde ebenso wie die Richtigkeit des Gesamtverfahrens durch systematische Untersuchungen belegt.

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Determination of se by furnace atomic absorption spectrometry (FAAS) in the ppb-range in Cu, Cu alloys, Ag, Au, Pb and Bi after volatilization in an oxygen stream

Summary Selenium is evaporated in a multi-stage procedure within 15 min from metals or metal oxides fused at temperatures of 1100–1150°C under a stream of oxygen and is trapped in a receiver cooled with liquid nitrogen. The condensed SeO₂ is dissolved with a definite volume of diluted HNO₃ in the presence of Ni-nitrate and determined with high sensitivity and reliability by FAAS (electrodeless discharge lamp). The detection limit of the FAAS was found to be 3 · 10^–11 g of Se. The multi-stage procedure allows to detect Se levels 0.05 ppb in Ag and Au, 0.1 ppb in Cu, 0.2 ppb in Bi, and 10 ppb in Pb, respectively, with sample weights 10 g. For wire, rod, and chip samples the coefficients of variation are found to be between 3 and 6% for Se contents of 2 to 0.002 ppm. The quantitative evaporation of Se from Cu, Ag, Au, and Bi as well as the accuracy of the whole procedure have been checked systematically.

Die Arbeit wurde durch Mittel der DFG in dankenswerter Weise unterstützt.     

Further applications of endocyclic enamine-enone annulations : The total syntheses of rac-Sceletium alkaloid A4 and 3'-demethoxy sceletium alkaloid A4

The total synthesis of rac-sceletium alkaloid A₄1a and of its 3'-demethoxy analogue 1b via the annulation of endocyclic enamines 4a–b is presented. The Michael acceptor 5a is a useful synthon for the two-step synthesis of 2,3-disubstituted pyridines from Δ²-pyrrolines.     

Photoelectron spectra of polyunsaturated [4,4,2]propellanes

The photoelectron spectra of the six propellanes 1 to 6 have been recorded. Those bands which correspond to ejection of an electron from a π-orbital have been assigned, using the concept of through bond and through space interaction. Homoconjugative interaction between the π-systems of the two butadiene moieties of 6 is of the same order as that of the π-orbitals in norbornadiene.