Zweij?hrige Erfahrung in der Routineanalyse mit einem C-N-H-Automaten

Zusammenfassung Unsere Erfahrungen bei der Routineanalyse von festen und flüssigen Verbindungen, die z.B. D, F, Cl, Br, J, S, Se, Cr, W, P, Bi, Si, Sn, Pb, Ti, B, Hg, Na, K, Cu, Ag, Au, Fe oder Ni enthalten, mit einem Automaten, der in einem. 10 min-Cyclus die Prozentgehalte von C, N und H. ausdruckt, werden mitgeteilt.

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Summary This paper communicates our experiences in routine analyses of solid and liquid compounds, containing elements such as D, F, Cl, Br, J, S, Se, Cr, W, P, Bi, Si, Sn, Pb, Ti, B, Hg, Na, K, Cu, Ag, Au, Fe or Ni with an automatic instrument which prints out the percentages of C, N and H within 10 minutes.

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Die angegebenen Werte stellen den Standardfehler dar.     

Principle and analytical applications of resonance lonization mass spectrometry

Resonance ionization mass spectrometry (RIMS) is a very sensitive analytical technique for the detection of trace elements. This method is based on the excitation and ionization of atoms with resonant laser light followed by mass analysis. It allows element and, in some cases, isotope selective ionization and is applicable to most of the elements of the periodic table. A high selectivity can be achieved by applying three step photoionization of the elements under investigation and an additional mass separation for an unambiguous isotope assignment.An effective facility for resonance ionization mass spectrometry consists of three dye lasers which are pumped by two copper vapor lasers and of a linear time-of-flight spectrometer with a resolution better than 2500. Each copper vapor laser has a pulse repetition rate of 6.5 kHz and an average output power of 30 W.With such an apparatus measurements with lanthanide-, actinide-, and technetium-samples have been performed. By saturating the excitation steps and by using autoionizing states for the ionization step a detection efficiency of 4 × 10^–6 and 2.5 × 10^–6 has been reached for plutonium and technetium, respectively, leading to a detection limit of less than 10⁷ atoms in the sample. Measurements of isotope ratios of plutonium samples were in good agreement with mass-spectrometric data. The high elemental selectivity of the resonance ionization spectrometry could be demonstrated.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Synthese „anorganischer”︁ Tintenfisch-Moleküle

Inorganic Pode-Type Molecules The reaction of monosubstituated polyethylenglykoles [m = 0—4, R = Cl, OCH₃, OAs(CH₃)₂, OSi(CH₃)₃] with amino compounds (CH₃)_xE[N(CH₃)₂]_y(E = Si, x = y = 2; E = Si, x = 1, y = 3; E = P, x = 0, y = 3; E = As, y = 0, y = 3) results in the formation of pode-type molecules of the formula . The synthesis and rearrangement of these compounds by heating is described.     

Investigation on elemental and isotopic fractionation during 196 nm femtosecond laser ablation multiple collector inductively coupled plasma mass spectrometry

Despite the large number of successful applications of laser ablation, elemental and isotopic fractionation coupled to inductively coupled plasma mass spectrometry (ICP-MS) remain as the main limitations for many applications of this technique in the fields of analytical chemistry and Earth Sciences. A substantial effort has been made to control such fractionations, which are well-established features of nanosecond laser ablation systems. Technological advancements made over the past decade now allow the ablation of solids by femtosecond laser pulses in the deep ultraviolet (UV) region at wavelengths less than 200 nm. Here the use of femtosecond laser ablation and its effects on elemental and isotopic fractionation is investigated. The Pb/U system is used to illustrate elemental fractionation and stable Fe isotopes are used to illustrate isotopic fractionation. No elemental fractionation is observed beyond the precision of the multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) measurements. Without a matrix match between standard and sample, elemental fractionation is absent even when using different laser ablation protocols for standardization and samples (spot versus raster). Furthermore, we found that laser ablation-induced isotope ratio drifts, commonly observed during nanosecond laser ablation, are undetectable during ultraviolet femtosecond laser ablation. So far the precision obtained for Fe isotope ratio determinations is 0.1‰ (2 standard deviation) for the ⁵⁶Fe/⁵⁴Fe ratio. This is close to that obtainable by solution multiple-collector inductively coupled plasma mass spectrometry. The accuracy of the results appears to be independent of the matrix used for standardization. The resulting smaller particle sizes reduce fractionation processes. Femtosecond laser ablation carries the potential to solve some of the difficulties encountered during the two prior decades since the introduction of laser ablation.     

Transaminierungen am dimethylamino-bis-(trifluormethyl)-arsin und -phosphin

The arsines and phosphines (CF₃)₂EN(CH₃)₂ (E= P or As) react with secondary amines with the formation of (CF₃)₂ENR₂ and HN(CH₃)₂. Mechanistic and steric effects associated with these reactions are discussed. The influence of the groups (CF₃)₂E on the E-N-bonding and the reaction is examined.     

Structural and oxidation-state changes at its nonstandard Ni-Fe site during activation of the NAD-reducing hydrogenase from Ralstonia eutropha detected by X-ray absorption, EPR, and FTIR spectroscopy

Structure and oxidation state of the Ni-Fe cofactor of the NAD-reducing soluble hydrogenase (SH) from Ralstonia eutropha were studied employing X-ray absorption spectroscopy (XAS) at the Ni K-edge, EPR, and FTIR spectroscopy. The SH comprises a nonstandard (CN)Ni-Fe(CN)(3)(CO) site; its hydrogen-cleavage reaction is resistant against inhibition by dioxygen and carbon monoxide. Simulations of the XANES and EXAFS regions of XAS spectra revealed that, in the oxidized SH, the Ni(II) is six-coordinated ((CN)O(3)S(2)); only two of the four conserved cysteines, which bind the Ni in standard Ni-Fe hydrogenases, provide thiol ligands to the Ni. Upon the exceptionally rapid reductive activation of the SH by NADH, an oxygen species is detached from the Ni; hydrogen may subsequently bind to the vacant coordination site. Prolonged reducing conditions cause the two thiols that are remote from the Ni in the native SH to become direct Ni ligands, creating a standardlike Ni(II)(CysS)(4) site, which could be further reduced to form the Ni-C (Ni(III)-H(-)) state. The Ni-C state does not seem to be involved in hydrogen cleavage. Two site-directed mutants (HoxH-I64A, HoxH-L118F) revealed structural changes at their Ni sites and were employed to further dissect the role of the extra CN ligand at the Ni. It is proposed that the predominant coordination by (CN),O ligands stabilizes the Ni(II) oxidation state throughout the catalytic cycle and is a prerequisite for the rapid activation of the SH in the presence of oxygen.