Some investigations on stability and precision of an HR-ICP-MS

Over a period of 4 months long- and short time stability (precision) of a high resolution inductively coupled plasma mass spectrometer (HR-ICP-MS) was investigated using an ELEMENT (Finnigan MAT, Germany) instrument. By using a special torch design, significant improvements could be achieved. Without changing any electrical parameters of the mass spectrometer, the long time stability over a time period of 4 months was measured as about ± 15% for ¹¹⁵In for all three steps of resolution (300, 3000, 7500). The short time stability over a period of 2–8 h was measured as about ± 10% (at maximum), also nearly independent of the resolution. The main result was the near independence of the stability from the mass-spectrometer itself, but a strong dependence on the sample introduction system, the ICP-torch and the cones. Received: 18 February 1997 / Revised: 16 June 1997 / Accepted: 19 June 1997     

The Synthesis and Dimerization of Transient 1-Silabutadienes

3-Methyl-1-tris(trimethylsilyl)silyl-2-butenol(1) ( 6 ) and (E)-3-Phenyl-1-tris(trimethylsilyl)silyl-2-propenol(1) ( 7 ) were prepared by the reaction of tris(trimethylsilyl)silyllithium ( 5 ) with 3,3-dimethylacrolein and (E)-cinnamaldehyde, resp. The alcohols 6 and 7 proved to be suitable precursors for the generation of the transient 1-silabutadienes (Me₃Si)₂Si = CHCH = CR¹R² 8 and 9 ( 8 : R¹ = R² = Me; 9 : R¹ = H, R² = Ph) following the principle of the modified Peterson reaction. Thus, 6 and 7 after deprotonation with excess MeLi in ether at low temperatures eliminated trimethylsilanolate and gave 8 and 9 , which were trapped by the excess organolithium reagent undergoing nucleophilic 1,2- or 1,4-addition reactions. In the absence of scavengers, e.g. when 8 and 9 were generated by treatment of 6 and 7 with stoichiometric quantities of MeLi in ether, the 1-silabutadienes dimerize in a [2 + 2] head-to-head fashion to give the 1,2-disilacyclobutanes 17 and 18 , resp., besides polymeric material. Treatment of the alcohol 6 with MeLi in tetrahydrofuran caused a 1,3-Si,O-trimethylsilyl shift affording the alkoxysilane (Me₃Si)₂SiH? CH(OSiMe₃)CH = CMe₂ 19 .     

Pathfollowing methods in nonlinear optimization III: Lagrange multiplier embedding

This paper deals with Lagrange multiplier methods which are interpreted as pathfollowing methods. We investigate how successful these methods can be for solving “really nonconvex” problems. Singularity theory developed by Jongen-Jonker-Twilt will be used as a successful tool for providing an answer to this question. Certain modifications of the original Lagrange multiplier method extend the possibilities for solving nonlinear optimization problems, but in the worst case we have to find all connected components in the set of all generalized critical points. That is still an open problem. This paper is a continuation of our research with respect to penalty methods (part I) and exact penalty methods (part II).     

The relative configuration of flavipucine

The relative configuration of the antibiotic flavipucine as inferred from a differential rearrangement reaction was confirmed by ozonolysis to a crystalline oxidoester amide identical with a specimen of this same compound prepared by synthesis.     

Microstructure development and properties of the AlCuFe quasicrystalline coating on near-α titanium alloy

A protective quasicrystalline AlFeCu coating was deposited on TIMETAL 834 substrate by nonreactive magnetron sputtering in order to improve resistance of the alloy to oxidation. Microstructure characterisation of the substrate and the coating was performed by analytical scanning- and transmission electron microscopy as well as X-ray diffractometry. Depending on annealing temperature and time, the deposited coating (2.7 μm thick) has a different microstructure. The coating in Specimen 1 (annealed 600 °C/4 h in vacuum) consisted of two zones: outer, composed of Al₅Fe₂ and Al₂Cu₃ phases and inner, in which only quasicrystalline ψ phase was present. The coating in Specimen 2 (annealed 600 °C/4 h + 700 °C/2 h in vacuum) was fully quasicrystalline and consisted of icosahedral ψ phase.Both coatings exhibit higher microhardness than the substrate material. It was established that the applied surface treatment essentially improves oxidation resistance of the alloy tested at 750 °C during 250 h in static air. Sample weight gain was 60% lower than in the case of uncoated sample. Oxide scale spallation occurred for uncoated alloy while the coated one did not show any spallation. It was found that the very brittle scale formed during oxidation on the uncoated alloy was consisting of TiO₂, while that on the coated one consisted mainly of α-Al₂O₃.     

Thermal Ionization and Inductively Coupled Plasma Mass Spectrometry: Potential for Application to Studies on the Biokinetics of Molybdenum in Humans

Abstract

The use of stable isotopes as tracers in biokinetic investigations provides a means to obtain important metabolic data directly in humans without exposing the subjects to undue risks. In this work, three types of mass spectrometers are compared with regard to the determination of the abundances of stable isotopes of molybdenum in natural and enriched aqueous samples. The data show a good response of thermal ionization mass spectrometry (TIMS) and of high-resolution inductively coupled plasma mass spectrometry (ICPMS) to the isotopic enrichment of the samples, whereas conventional quadrupole ICPMS shows an unsatisfactory reproducibility of the results. Moreover, only TIMS can achieve an accuracy of better than 1% for the obtained isotopic ratios. Although a tedious procedure for the preparation of the biological samples is required and less sensitivity is achieved as compared to ICPMS, TIMS still seems to be method of choice for the accurate assessment of isotope ratios as required in multitracer studies on human biokinetics of trace metals.     

D-homosteroids Boat conformation of the D-ring

Chemical evidence is cited in support of the boat conformation of ring-D in certain D-homosteroids. The interconversion of ketolic isomers ostensibly by methyl migration is presented.     

Die ɛ-Störung linearer und quadratischer Optimierungsaufgaben und ihre Anwendung auf das Hildreth-Verfahren

Zusammenfassung Durch eine -Störung in der Diagonalen der quadratischen Form kann man eine lineare oder quadratisch semidefinite Optimierungsaufgabe zu einer streng definiten quadratischen Aufgabe machen, so daß Lösungsverfahren, die die Formmatrix als nichtsingulär voraussetzen müssen, anwendbar werden. Bekanntlich konvergiert die Lösungx der -gestörten Aufgabe für 0 gegen den Lösungsvektorx ^m von minimalem Betrag der ursprünglichen Aufgabe. Wir zeigen darüber hinaus, daß im linearen Fall immer und im eigentlich quadratischen in gewissen Fällen schon für 0<<* die beiden Lösungenx undx ^m übereinstimmen. Im linearen Fall ist die obere Grenze * durch die Lösung eines linearen Ungleichungssystems gegeben.Im zweiten Abschnitt wenden wir dasHildreth-Verfahren mittels der -Störung auf lineare und quadratisch semidefinite Aufgaben an, diskutieren Konvergenz- und Genauigkeitsfragen und kommen zu dem Schluß, daß man in der Praxis sowohl bei Rechnung von Hand als auch bei maschineller Rechnung zu befriedigenden Ergebnissen kommt.

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Summary Linear and quadratic semidefinite programming problems may be transformed into strongly definite quadratic problems by means of an -perturbation of the quadratic form so that procedures which presuppose the matrix of the form to be nonsingular, may be applied. As is well known, the solutionx of the -perturbated problem converges to the solutionx ^m of minimal length of the original problem as 0. We show that always in the linear case and in the quadratic case under certain circumstances, both solutionsx andx ^m are equal if 0 <<*. In the linear case, the upper limit * is given by the solution of a system of linear inequalities.In the second part of this paper we apply the method ofHildreth to linear and quadratic semidefinite programming problems by the -perturbation. We discuss questions of convergence and exactness, and conclude that in practice calculation by hand as well as by computer leads to satisfying results.

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Der Verfasser ist Herrn Prof. Dr.W. Vogel, Bonn, für einen Hinweis zu Dank verpflichtet.

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Vorgel. v.:H. P. Künzi