Identification of low molecular vaporizable components in silicone resins using gas chromatography/mass spectrometry

An experimental set-up for the detection of elemental chlorine in chlorinated hydrocarbons (CHCs) is described based on a miniaturized system, which could be used for on-line monitoring of chlorinated compounds. With an optimized time-resolved detection chlorine from CHCs like CCl₄ can be determined by Laser-Induced-Breakdown-Spectroscopy (LIBS) with g/g-detection limits in the gas phase. The application of a miniaturized Nd : YAG laser resulted only in a minor loss in performance, hence it could be used for designing a rugged and small on-line sensor. In addition, preliminary results for the detection of chlorine via the formation of CuCl in the plasma formed by focussing the laser on a copper surface are reported. Utilizing the luminescence of the CuCl D-system at 440 nm, a tenfold improvement in the detection limits was obtained. It appears that the formation of ad hoc selected, small molecules in a laser plasma could be a promising alternative for the selective and sensitive analysis of gaseous chlorinated and other species.     

A Self‐Improved Water‐Oxidation Catalyst: Is One Site Really Enough?

The homogeneous catalysis of water oxidation by transition‐metal complexes has experienced spectacular development over the last five years. Practical energy‐conversion schemes, however, require robust catalysts with large turnover frequencies. Herein we introduce a new oxidatively rugged and powerful dinuclear water‐oxidation catalyst that is generated by self‐assembly from a mononuclear catalyst during the catalytic process. Our kinetic and DFT computational analysis shows that two interconnected catalytic cycles coexist while the mononuclear system is slowly and irreversibly converted into the more stable dinuclear system: an extremely robust water‐oxidation catalyst that does not decompose over extended periods of time.     

The invisible Majorana bound state at the helical edge

The presence of a Majorana bound state in condensed matter systems is often associated to a zero bias peak in conductance measurements. Here, we analyze a system were this paradigm is violated. A Majorana bound state is always present at the interface between a quantum spin Hall system that is magnetically gapped and a quantum spin Hall system gapped by proximity induced s-wave superconductivity. However, the linear conductance could be either zero or non-zero and quantized depending on the energy and length scales of the barriers. The transition between the two values is reminiscent of the topological phase transition in proximitized spin–orbit coupled quantum wires in the presence of an applied magnetic field. We interpret the behavior of the conductance in terms of scattering states at both zero and non-zero energy.     

Identification of low molecular vaporizable components in silicone resins using gas chromatography/mass spectrometry

Silicone resins can be used as polymeric precursors in the production of ceramic materials. Cohydrolysis of mixtures of trimethylchlorosilane, methyldichlorosilane, vinylmethyldichlorosilane and phenyltrichlorosilane leads to the formation of especially suitable polysiloxanes, but also low-molar mass siloxanes are formed as undesired by-products. The structures of these by-products have been elucidated. Vaporizable components of the matrix have been isolated by distillation, separated using gas chromatography and identified by mass spectrometry in EI (electron impact ionization) and CI (chemical ionization with isobutane) mode. The EI mass spectra of the siloxane oligomers with different numbers of Si-H, Si-phenyl and Si-vinyl groups show characteristic fragments like Me₃Si⁺, ViMe₂Si⁺, Vi₂MeSi⁺, PhMe₂Si⁺, and Ph₂MeSi⁺, which give a first indication to the structure, but generally do not show molecular peaks. A reliable determination of the molar mass has been possible considering the CI-ions and CI-fragments [M+1]⁺, [M−1]⁺, [M−27]⁺ and [M−77]⁺, respectively. The compounds M₂D^Ph,OH and M₃T^Ph have been identified as main components of the investigated siloxane mixture. Besides, numerous linear compounds of the type M₂(D^H)n(D^Vi)_m and M₂T^Ph(D^H)_n(D^Vi)_m M as well as cyclic ones of the structure [MT^Ph(D^H)_n(D^Vi)_m] with n, m=0–3 have been indicated. Received: 3 March 1995/Revised: 25 March 1995/Accepted: 3 April 1995     

Analysis of siloxane pyrolysis products by cryo-GC/FT-IR and GC/MS

On line measurements of infrared and mass spectra of siloxane pyrolysis products separated by gas chromatography are described. The FT-IR absorbance spectra have been recorded from the eluates trapped as small spots on a moving window held at 77 K. Three of the main compounds separated were selected for FT-IR identification performed by comparing the spectra with GC/MS data and by spectral searching using a library of compounds measured under the same conditions.Dedicated to our most honourable teacher Professor Dr. H. Kriegsmann on the occasion of his 70th birthday     

Evaluation of protein loading techniques and improved separation in OFFGEL isoelectric focusing

2-DE proved to be a key technology in protein science since the two orthogonal separation dimensions are capable of protein isoform separation. Recently, Agilent introduced the OFFGEL 3100 fractionator for in solution IEF (off-gel) of proteins with the help of a 12- or 24-well frame. With this instrument also conventional focusing in IPG strips after passive in-tray rehydration can be performed. In this study, two novel IEF applications using the OFFGEL electrophoresis were developed. First, a sample cup was built and a cup-loading method for the OFFGEL device was implemented. Applying proteins via cup resulted in higher reproducibility and less protein loss compared with conventional in-tray rehydration loading. Especially, the recovery of basic and high-molecular-mass proteins seems to be favored by cup loading. These effects are more pronounced with low microgram sample amounts. Second, a 48-well OFFGEL frame was developed, which doubles the resolution of the commercially available 24-well frame. It is capable of separating proteins with small pI differences and shows potential for isoform/PTM separation.     

Supercritical fluid chromatography (SFC) of linear and cyclic components in technical silicone oils

Since technical silicone oils are widely used, high performance analysis and exact quality control are necessary. The quantity of low molecular cyclic components is of special importance for the properties of the oils. Supercritical Fluid Chromatography (SFC) provides a facility for determining such cyclic components. Accurate assignment of linear and cyclic polydimethylsiloxanes is possible by coupling SFC with mass spectrometry (MS) or by using standard materials.     

A Self‐Improved Water‐Oxidation Catalyst: Is One Site Really Enough?

The homogeneous catalysis of water oxidation by transition‐metal complexes has experienced spectacular development over the last five years. Practical energy‐conversion schemes, however, require robust catalysts with large turnover frequencies. Herein we introduce a new oxidatively rugged and powerful dinuclear water‐oxidation catalyst that is generated by self‐assembly from a mononuclear catalyst during the catalytic process. Our kinetic and DFT computational analysis shows that two interconnected catalytic cycles coexist while the mononuclear system is slowly and irreversibly converted into the more stable dinuclear system: an extremely robust water‐oxidation catalyst that does not decompose over extended periods of time.