Automated and rapid online determination of 15N abundance and concentration of ammonium, nitrite, or nitrate in aqueous samples by the SPINMAS technique

On the basis of the principle of reaction continuous-flow quadrupole mass spectrometry, an automated sample preparation unit for inorganic nitrogen (SPIN) species was developed and coupled to a quadrupole Mass Spectrometer (MAS). The SPINMAS technique was designed for an automated, sensitive, and rapid determination of 15N abundance and concentration of a wide variety of N-species involved in nitrogen cycling (e.g. NH4+, NO3-, NH2OH etc.). In this paper, the SPINMAS technique is evaluated with regard to the determination of 15N abundance and concentration of the most fundamental inorganic nitrogen compounds in ecosystems such as NH4+, NO2-, and NO3-. The presented paper describes the newly developed system in detail and demonstrates the general applicability of the system. For a precise determination of 15N abundance and concentration, a minimum total N-amount of 10 microg NH4+ - N, 0.03 microg NO2- - N, or 0.3 microg NO3- - N has to be supplied. Currently, the SPINMAS technique represents the most rapid and only fully automated all-round method for a simultaneous determination of 15N abundance and total N-amount of NH4+, NO2-, or NO3- in aqueous samples.     

A novel monochromator for experiments with ultrashort X‐ray pulses

Aiming at advancing storage‐ring‐based ultrafast X‐ray science, over the past few years many upgrades have been undertaken to continue improving beamline performance and photon flux at the Femtoslicing facility at BESSY II. In this article the particular design upgrade of one of the key optical components, the zone‐plate monochromator (ZPM) beamline, is reported. The beamline is devoted to optical pump/soft X‐ray probe applications with 100 fs (FWHM) X‐ray pulses in the soft X‐ray range at variable polarization. A novel approach consisting of an array of nine off‐axis reflection zone plates is used for a gapless coverage of the spectral range between 410 and 1333 eV at a designed resolution of E/ΔE = 500 and a pulse elongation of only 30 fs. With the upgrade of the ZPM the following was achieved: a smaller focus, an improved spectral resolution and bandwidth as well as excellent long‐term stability. The beamline will enable a new class of ultrafast applications with variable optical excitation wavelength and variable polarization.     

Microswimmers – From Single Particle Motion to Collective Behavior

Locomotion of autonomous microswimmers is a fascinating field at the cutting edge of science. It combines the biophysics of self-propulsion via motor proteins, artificial propulsion mechanisms, swimming strategies at low Reynolds numbers, the hydrodynamic interaction of swimmers, and the collective motion and synchronisation of large numbers of agents. The articles of this Special Issue are based on the lecture notes of an international summer school, which was organized by the DFG Priority Programme 1726 “Microswimmers – From Single Particle Motion to Collective Behaviour” in the fall of 2015. The minireviews provide a broad overview of the field, covering both elementary and advanced material, as well as selected areas from current research.     

The structure of solid salt eutectics — – Why lamellar or conglomerate?

Using KCl/ZnSO₄ eutectic it has been shown that cooling the melt into a room temperature enclosure forms a lamellar structure, whereas cooling into a heated enclosure (225 °C) forms a conglomerate structure, while an enclosure temperature of 125 °C gave a partially conglomerate structure with some lamellae in process of forming conglomerates.Consideration of the thermal gradients imposed on solidification and consequently the relative time available during which the ions are sufficiently mobile to rearrange their positions, can explain the observation that lamellar structures are formed by higher melting point eutectics, whereas eutectics of lower melting point form conglomerate structures.     

Wurtzitan (Tetracyclo[5.3.1.12,6.04,9]dodecan)

A new synthesis of wurtzitane (13) is described starting from 2-oxo-protoadamant-4-ene (2). The key intermediate ketone 7 was obtained by regiospecific ring expansion of the β-amino alcohol 6. Entry to the wurtzitane system involved solvolysis of the tricyclic unsaturated mesylate 10 (→11).     

Formation of Ad-Layers and Clusters on Condensation of Metal Vapors on Solid Surfaces

Synthesis of organometallic materials can be accomplished in many cases by cocondensation of metal atoms and organic molecules at low temperatures. The reaction kinetics is determined by the competition between metal cluster growth and formation of the organometallic compound. Interesting compounds may contain one or more metal atoms; the latter type could be obtained by reaction between a cluster containing the desired number of metal atoms and an organic molecule. A precise knowledge of the events occurring on condensation of metal atoms and cluster formation can therefore be of value in the control of chemical synthesis. These phenomena have been investigated in connection with the study of the growth of thin metallic films, both experimentally and theoretically. Direct observation of the formation of very small clusters is difficult. The good agreement between experimental results and recent calculations for the development of large clusters, however, allows reliable theoretical conclusions for the first stages of adsorption and cluster formation. The present contribution describes experimental work on film growth and relevant theoretical concepts, and an attempt is made to develop applications to organometallic synthesis.     

Vergleichende Untersuchungen an polarographischen Analysenverfahren

The universal voltammetric instrument, described in part I of this series, is used for comparative studies on the most important polarographic methods, direct current, derivative pulse, simple and phase-sensitive alternating current, double-tone, and harmonic-wave polarography. In general the peak-heights of these methods are influenced in the same measure by the composition of base electrolyte. In single cases characteristic differences are observed.     

Invers-voltammetrische Bestimmung von Chrom(III)

Solutions of Cr(III) salts containing ammonium hydroxide and ammonium salts can be determined after proper pretreatment by inverse voltammetry at carbon paste and glassy carbon electrodes. The determination may be performed, too, with organic solutions of the Cr(III) oxinate. Sensitivity is 5 × 10^?7 M (= 26 ng Cr/ml), standard deviation is in the range of 4–6%.