Membrane Introduction Mass Spectrometry (MIMS): A Versatile Tool for Direct,Real‐Time Chemical Measurements

Membrane introduction mass spectrometry (MIMS) is a direct, continuous, on‐line measurement technique. It utilizes a membrane to semi‐selectively transfer analyte mixtures from a sample to a mass spectrometer, rejecting the bulk of the sample matrix, which can be a gas, liquid or solid/slurry. Analyte selectivity and sensitivity are affected by optimizations at the membrane, ionization and the mass spectrometer levels. MIMS can be roughly classified by the acceptor phase that entrains analyte(s) to the mass spectrometer after membrane transport, either a gaseous acceptor phase (GP‐MIMS) or condensed acceptor phase (CP‐MIMS). The aim of this article is to provide an introduction to MIMS as a technique and to explore current variants, recent developments and modern applications, emphasizing examples from our group, the Applied Environmental Research Laboratories as well as selected work from others in this emerging area. Also provided is a synopsis of current and future directions for this versatile analytical technique. Copyright © 2014 John Wiley & Sons, Ltd.     

ANALYZING THE RED-SHIFT CHARACTERISTICS OF AZULENIC,NAPHTHYL, OTHER RING-FUSED AND RETINYL PIGMENT ANALOGS OF BACTERIORHODOPSIN*

Prompted by the near infrared-absorbing properties of some of the azulenic bacteriorhodopsin (bR) analogs, we have analyzed their absorption characteristics along with 11 new related ring-fused analogs and the corresponding Schiff bases (SB) and protonated Schiff bases (PSB). The following three factors are believed to contribute to the total red shift of each of the pigment analogs (α_RS): perturbation of the basic chromophore (SB shift, ΔSB), protonation of the SB (PSB shift, PSBS) and protein perturbation (the opsin shift, OS). For each factor, effects of structural modifications were examined. For the red-shifted pigments, percent OS has been suggested as an alternate way of measuring protein perturbation. Computer-simulated chromophores provided evidence against any explanation involving altered shapes of the binding pocket as a major cause for absorption differences. Implications of the current bR results on preparation of further red-shifted bR and possible application to visual pigment analogs are discussed.     

Search for elastic muon-neutrino electron scattering

One possible event of the process ν^?_μ + e^? → v^?_μ + e^? has been observed. The various background processes are discussed and the event interpreted in terms of the Weinberg theory. The 90% confidence limits on the Weinberg parameter are 0.1 < sin²θ_W < 0.6.     

Observation of neutrino-like interactions without muon or electron in the gargamelle neutrino experiment

Events induced by neutral particles and producing hadrons, but no muon or electron, have been observed in the CERN neutrino experiment. These events behave as expected if they arise from neutral current induced processes. The rates relative to the corresponding charged current processes are evaluated.     

A semi‐quantitative approach for the rapid screening and mass profiling of naphthenic acids directly in contaminated aqueous samples

We report the use of a direct sampling, online analytical approach for the determination of acid extractable naphthenic acids in complex aqueous samples, known as condensed phase membrane introduction mass spectrometry (CP‐MIMS). The technique employs a capillary hollow fibre semi‐permeable membrane probe configured for immersion into a pH adjusted sample. A continuously flowing methanol acceptor phase transfers naphthenic acids to an electrospray ionization source, operated in negative ion mode, whereupon they are analysed by mass spectrometry as [M–H]^? ions. High‐resolution mass spectrometry is used to characterize the influence of sample pH on membrane transport of multiple components of complex naphthenic acid mixtures. We demonstrate the use of CP‐MIMS for semi‐quantitative analysis of real‐world samples using selected ion monitoring and full scan mass spectra at unit mass resolution. The technique has also been employed to continuously monitor the temporal evolution in the mass profile and concentrations of individual naphthenic acid isomer classes in heterogeneous solutions during adsorption processes. Copyright © 2015 John Wiley & Sons, Ltd.     

Renewable energy investments under different support schemes: A real options approach

This paper adopts a real options approach to analyze investment timing and capacity choice for renewable energy projects under different support schemes. The main purpose is to examine investment behavior under the most extensively employed support schemes, namely, feed-in tariffs and renewable energy certificate trading. We consider both multiple sources of uncertainty under each support scheme and uncertainty with respect to any change of support scheme, and we obtain both analytical (when possible) and numerical solutions. In a Nordic case study based on wind power, we find that the feed-in tariff encourages earlier investment. Nevertheless, as investment has been undertaken, renewable energy certificate trading creates incentives for larger projects. In our baseline scenario and taking the fixed feed-in tariff as a base, the revenue required to trigger investments is 61% higher with renewable certificates. At the same time, investment capacity is 61% higher.     

Spectroscopic diagnostics of temperature-controlled trench etching of silicon

Ernission from the plasma species CCl, CN, CO, N₂, and Si was monitored during trench etching of silicon with a CHCl,₃/ N, chemistry. The temperature of the backside of the wafer was recorded simultaneously. The emission response to experimentally induced perturbations of the plasma was found to be particularly informative. One such perturbation was a sudden change of the wafer temperature through control of the He pressure under the wafer. The other perturbation involved a drastic change of the N₂, flow rate. Our results confirm the mechanism of control of the trench profile through the temperature-dependent rate of deposition of polymers on the sidewalls during etch. Further, N₂, which certainly plays a crucial role in this chemistry, may engage in a surface reaction producing CN radicals; our data are consistent with this surface reaction. Finally, an algorithm was constructed for real-time monitoring of the selectivity of .silicon to the oxide mask; selectivity is shown to be very sensitive to the presence of N₂.     

LMTO Band Structure Calculations of ThCr2Si2-Type Transition Metal Compounds

The electronic structures of ThCr₂Si₂-type compounds were studied by means of self-consistent LMTO band structure calculations. Different bonding interactions in SrRh₂P₂are analyzed and their dependence on the electron count are discussed in terms of the formal substitution of elements. The overall bonding situation can be characterized as an interplay between covalent, metallic, and ionic interactions, although metal–metal bonding plays an important role. Particularly, the evolution of the interlayer bonding between the nonmetal atoms by changing the transition metal is examined in more detail. It turns out that the shortening of the interlayer bonds by filling thedshell of the transition metal is due to an increasing occupation of nonmetal bonding states which are pushed up to the vicinity of the Fermi level by antibonding metal–nonmetal interactions. The band structures of superconducting LuNi₂B₂C and nonsuperconducting SrRh₂P₂are compared and their similarities are pointed out. A van Hove singularity, generated by metal–metal interaction, coincides with the Fermi level in LuNi₂B₂C and lies about 0.2eV higher in SrRh₂P₂. By doping, it should be possible to induce superconductivity in SrRh₂P₂and related compounds.