Magnetic and crystal structure of copper(II) fluoride

A powder sample of the monoclinic, weak ferromagnet CuF₂ was investigated by neutron diffraction. Using the profile method, the crystal structure was refined and the spin configuration determined. The layer type structure with planar quadratic fluorine coordination of Cu²⁺ (3d⁹) and the magnetic structure are remarkably similar to those of AgF₂. The spin configuration is however different from the magnetic structures of other 3d-fluorides; the magnetic unit cell is doubled with respect to the chemical cell (a_m = 2a, P2₁/c). The ordered magnetic saturation moment corresponds to quenched orbital momentum.     

Thermospray liquid chromatographic—mass spectrometric multi-residue determination of 128 polar pesticides in aqueous environmental samples

Thermospray (TSP) ionization was evaluated with respect to its suitability in the LC-MS determination of a broad range of pesticides. The sensitivity and the selectivity of this method for the determination of 128 pesticides having a wide range of structures and polarities were investigated. An LC separation in combination with postcolumn addition of a volatile salt solution was developed, which permits the analysis of 95 pesticides with a single LC-MS method using reversed-phase gradient caution. The retention data and TSP mass spectra of these compounds are presented. The advantages of TSP postcolumn techniques in comparison with conventional systems are discussed. The application of this method to the analysis of an environmental sample (river water) spiked with eight phenylureas is demonstrated. lie method was evaluated with respect to detection limit, linearity and reproducibility. In addition, a simple method for enhancing the structural information from TSP spectra is reported, which makes use of specific instabilities found with many pesticides. As an example, possibilities for the confirmatory analysis of carbamates are described.     

Preparative mass‐spectrometry profiling of minor concentrated metabolites in Salicornia gaudichaudiana Moq by high‐speed countercurrent chromatography and off‐line electrospray mass‐spectrometry injection

Salicornia species have just been introduced to the European market as a vegetable named ‘samphire’, ‘green asparagus’, or ‘sea asparagus’. Due to its increasing attention, and associated value, minor compounds of Salicornia gaudichaudiana Moq were investigated. The use of countercurrent chromatography and mass spectrometry enabled the search for known, as well as potentially novel natural products. Their identification was achieved based on molecular weights and mass‐spectrometric fragmentation data. Low detection limits enabled the visualization of all compounds with their identification in almost real time close to the preparative countercurrent chromatography experiment. A list of known natural products from Salicornia genus guided the identification process of compounds occurring in Salicornia gaudichaudiana Moq by tandem mass spectrometry fragment comparison. The natural product classes were divided into four groups: chlorogenic acid derivatives; flavonoid derivatives; pentacyclic triterpenoid saponins; and other compounds.     

Isolation and structure determination of a lignan from the bark of Salix alba

A lignan, sisymbrifolin (1) found in the fruits of Solanum sisymbriflolium has been isolated from the bark extract of Salix alba (Salicaceae). Its structure was elucidated by its direct spectrum data of ESI-MS and one- and two-dimensional NMR spectroscopy for the first time.     

Determination of Li, Na, Mg, K, Ca and Fe with ICP-MS using cold plasma conditions

Some important analytes in ICP-MS are interfered by plasma argon or argon species, such as ArO⁺ and ⁵⁶Fe, ⁴⁰Ar and K or Ca. One approach to overcome this interference is the use of reduced forward power and a metal shield inserted between torch and load coil. These so called cold plasma conditions reduce the background caused by argon species and the formerly interfered analytes can be easily detected in the ng/g-range. Other elements in the lower mass region also profit from these conditions even when they are not interfered in normal plasma mode. The limits of detection are improved due to reduced background noise level and enhanced ion transmission. On the other hand, the reduced power fed to the plasma lowers the analytical performance and makes it susceptible to matrix effects. Elements of higher mass generally show higher detection limits compared to normal plasma mode. Received: 30 November 1998 / Revised: 4 February 1999 / Accepted: 8 February 1999     

Iron Precursor Decomposition in the Magnesium Combustion Flame: A New Approach for the Synthesis of Particulate Metal Oxide Nanocomposites

Powders of Fe–Mg–O nanocomposite particles have been grown using a novel chemical vapor synthesis approach that employs the decomposition of a metalorganic precursor inside the metal combustion flame. After annealing in controlled gas atmospheres composition distribution functions, structure and phase stability of the obtained magnesiowüstite nanoparticles are measured with a combination of techniques such as inductively coupled plasma‐optical emission spectroscopy, energy dispersive X‐ray spectroscopy, X‐ray diffraction, and scanning and transmission electron microscopy. Complementary Mössbauer spectroscopy measurements reveal that depending on Fe loading and temperature of annealing either metastable and superparamagnetic solid solutions of Fe³⁺ ions in periclase (MgO) or phase separated mixtures of MgO and ferrimagnetic magnesioferrite (MgFe₂O₄) nanoparticles can be obtained. The described combustion technique represents a novel concept for the production of mixed metal oxide nanoparticles. Adressing the impact of selected annealing protocols, this study underlines the great potential of vapor phase grown non‐equilibrium solids, where thermal processing provides means to trigger phase separation and, concomitantly, the emergence of new magnetic properties.     

N‐Z‐Pro–d‐Leu using synchrotron radiation data from a very small crystal

The crystal structure of the neuroactive artificial dipeptide N‐­benzyl­oxy­carbonylprolyl‐d ‐leucine, C₁₉H₂₆N₂O₅, was solved using synchrotron radiation data collected on a very small crystal (20 × 20 × 380 μm). The mol­ecules form hydrogen‐bonded 2₁ helices. The acid carbonyl group does not participate in strong hydrogen bonds. This is interpreted as a consequence of close‐packing requirements.