Background and line interference corrections in quantitative GD-OES – New approaches to an old problem

The origin of radiative background in GD-OES is discussed, in connection with the problem of multi-matrix measurements in depth profile analysis. Backed by some experimental evidence in the form of line scans, it is argued that line emission from sample material and the plasma gas (Ar) make up the dominating contributions to the radiative background. The contribution from Ar, in this work termed Matrix-independent Background (MIB), is investigated in more detail. It is shown that, at constant voltage and current, the Ar emission intensity is nearly constant and independent of the pressure, but somewhat matrix-dependent. It is suggested that the MIB can be expressed as a linear function of the intensity of an Ar reference line. This idea is tested experimentally by making intensity measurements on a large set of calibration standards of varying composition. The results are fitted to a calibration function which allows optional definitions of the MIB. It is shown that with a MIB defined as a linear function of the Ar intensity, the different contributions to the spectral background can be more accurately determined than with the MIB defined as a constant.     

New hardware for radio frequency powered glow discharge spectroscopies and its capabilities for analytical applications

A new radio frequency (rf) hardware is developed for glow discharge spectroscopic methods. The resulting features and its capabilities for analytical applications are discussed. The electrical equipment developed allows to work as quickly, stably, reliably and easily as known from the direct current (dc) mode. Moreover, the rf power measurement has been improved. The hardware has been developed, optimised and tested for glow discharge optical emission spectroscopy (GDOES), but nevertheless it is possible to use it for all procedures applying glow discharge sources.     

Quantitative depth profiling in glow discharge spectroscopies – A new deconvolution technique to separate effects of an uneven erosion crater shape

An algorithm is presented as a concept for the quantification in direct current and radiofrequency glow discharge (GD) modes for GD optical emission spectroscopy. The algorithm is divided into excitation and sputtering part and thus it is possible to distinguish between the different excitation processes and to consider equivalent sputtering crater formations in both modes. Intensity-time profiles are affected corresponding to the method by several effects. One important effect is that sputtering occurs at a single time in different depths because of curved crater bottoms, this is usually called crater effect. The main purpose is to introduce an iterative deconvolution technique which for the quantification numerically takes into account the curved sputtering crater bottom. Input data for the deconvolution technique are the calibrated mass-time profile, the partial densities of the sample constituents and the measured final shape of the sputtering crater. Using a relatively simple model for ion sputtering the deconvolution technique improves iteratively the calculated layer structure by means of information on crater formation. The mathematical handling is illustrated for the quantification of a depth profile of a multilayer sample of ten 100 nm layers. The resulting concentration-depth profile reflects excellently the real elemental distribution of the multilayer system.     

Instrumental neutron activation analysis of Elbe river suspended particulate matter separated according to the settling velocities

Suspended particulate matter in Elbe river water near Hamburg has been separated into different fractions by pouring the samples into special sedimentation tubes called Atterberg cylinders. The fractions are obtained by decanting the water after different settling periods, and by filtrating the decanted part. The analysis is done by neutron activation in the absolute mode, after irradiation periods of 5 min and 3 days. Mean settling velocities of the SPM-mass and the elements determined have been calculated.     

Controlling 6-endo-selectivity in oxidation/bromocyclization cascades for synthesis of aplysiapyranoids and other 2,2,6,6-substituted tetrahydropyrans

A cascade, composed of (i) oxovanadium(V)-catalyzed oxidation of bromide by tert-butyl hydroperoxide and (ii) stereoselective 6-endo-bromocyclization, affords 3-bromo-2-aryl-2,6,6-trimethyltetrahydropyrans from styrene-type tertiary alkenols in synthetically useful yields. (E)-Alkenols add the bromo- and the alkoxy substituent anti-selectively across the double bond, indicating a bromonium ion-mechanism for the ring closure. 6-endo-control of the alkenol cyclization thereby arises from the polar effect of the aryl substituent. Two methyl substituents bound to the alkene terminus are not similarly able to favor 6-endo-cyclization, because strain arising from methyl group repulsion, as the bromonium-activated π-bond and the hydroxyl oxygen approach, directs bromocyclization of tertiary prenyl-type substrates toward tetrahydrofuran formation. A hexasubstituted bromotetrahydropyran prepared from the oxidation/bromocyclization cascade served as starting material for synthesis of racemic aplysiapyranoid A, in a sequence of free radical and polar functional group interconversion.     

Nano and rapid resolution liquid chromatography–electrospray ionization–time of flight mass spectrometry to identify and quantify phenolic compounds in olive oil

The applicability of nanoLC‐ESI‐TOF MS for the analysis of phenolic compounds in olive oil was studied and compared with a HPLC method. After the injection, the compounds were focused on a short capillary trapping column (100 μm id, effective length 20 mm, 5 μm particle size) and then nanoLC analysis was carried out in a fused silica capillary column (75 μm id, effective length 10 μm, 3 μm particle size) packed with C18 stationary phase. The mobile phase was a mixture of water + 0.5% acetic acid and ACN eluting at 300 nL/min in a gradient mode. Phenolic compounds from different families were identified and quantified. The quality parameters of the nanoLC method (linearity, LODs and LOQs, repeatability) were evaluated and compared with those obtained with HPLC. The new methodology presents better sensitivity (reaching LOD values below 1 ppb) with less consumption of mobile phases, but worse repeatability, especially inter‐day repeatability, resulting in more difficulties to get highly accurate quantification. The results described in this article open up the application fields of this technique to cover a larger variety of compounds and its advantages will make it especially useful for the analysis of samples containing low concentration of phenolic compounds, as for instance, in biological samples.     

Snapshot location for POD in control of a linear heat equation

In the present work, we study the approximation of a distributed optimal control problem for a linear heat equation with model order reduction based on Proper Orthogonal Decomposition (POD-MOR). We show that snapshot location for control problems is crucial in model reduction. For the determination of the time instances (snapshot locations) we utilize an a-posteriori error control concept which is based on a reformulation of the optimality system of the underlying optimal control problem as a second order in time and fourth order in space elliptic system. Finally, we present a numerical test to illustrate our approach. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gas Forming Processes within Lignite Mining Dumps

Abstract

Gas analyses of the soil atmosphere of lignite mining dumps yielded increased contents of carbon dioxide. To get information about the potential sources and the carbon dioxide releasing capacity of the dumps, samples of dump material were investigated for their contents and isotopic compositions of organic and inorganic carbon as well as the carbon dioxide in the soil atmosphere. The contents of organic and inorganic carbon were found to vary depending on type of dump material. The isotopic composition of the organic carbon ranges between ?24.5 and ?26.5‰, which is typical for humous materials. The carbonates are found to be of marine origin (δ¹³C: +0.5 to ?1.1‰). By means of the isotope investigations it could be shown that the carbon dioxide in the lignite mining dump arises from these two different sources. Mixing ratios can be calculated using the isotope balance equation. Both reaction paths are associated with oxygen consumption and do not result in an increased gas pressure within the dump.     

Modellrechnungen zur Isotopentrennung durch Multiphotonen-Photodissoziation von Molekülen

Für stoßfreie SF₆-Moleküle werden Mulltiphotonen-Photofragmentierungswahrscheinlichkeiten im intensiven IR-LASER-Feld berechnet einschließlich der Isotopenselektivität derartiger Prozesse in Abhängigkeit von der eingestrahlten LASER-Linie, der Leistungsdichte, dem Impulsprofil und der Temperatur. Über ein quantenmechanisches Modell werden die Rotationsschtwingungsniveaus des SF₆-Moleküls, die Verstimmung zwischen LASER- und Molekülschwin-gungsfrequenz und die intramolekulare Schwingungsrelaxation berücksichtigt.