Evaluation of direct analysis in real time mass spectrometry for onsite monitoring of batch slurry reactions

Batch slurry reactions are widely used in the industrial manufacturing of chemicals, pharmaceuticals, petrochemicals and polymers. However, onsite monitoring of batch slurry reactions is still not feasible in production plants due to the challenge in analyzing heterogeneous samples without complicated sample preparation procedures. In this study, direct analysis in real time mass spectrometry (DART-MS) has been evaluated for the onsite monitoring of a model batch slurry reaction. The results suggested that automation of the sampling process of DART-MS is important to achieve quantitative results. With a sampling technique of manual sample deposition on melting point capillaries followed by automatic sample introduction across the helium beam, relative standard deviation (RSD) of the protonated molecule signals from the reaction product of the model batch slurry reaction ranged from 6 to 30%. This RSD range is improved greatly over a sampling technique of manual sample deposition followed by manual sample introduction where the RSDs are up to 110%. Furthermore, with the semi-automated sampling approach, semi-quantitative analysis of slurry samples has been achieved. Better quantification is expected with a fully automated sampling approach.     

Characterization of the carrot defect in 4H-SiC epitaxial layers

Characterization of the epitaxial defect known as the carrot defect was performed in thick 4H-SiC epilayers. A large number of carrot defects have been studied using different experimental techniques such as Nomarski optical microscopy, KOH etching, cathodoluminescence and synchrotron white beam X-ray topography. This has revealed that carrot defects appear in many different shapes and structures in the epilayers. Our results support the previous assignment of the carrot defect as related to a prismatic stacking fault. However, we have observed carrot defects with and without a visible threading dislocation related etch pit in the head region, after KOH etching. Polishing of epilayers in a few μm steps in combination with etching in molten KOH and imaging using Nomarski optical microscope has been used to find the geometry and origin of the carrot defects in different epilayers. The defects were found to originate both at the epi-substrate interface and during the epitaxial growth. Different sources of the carrot defect have been observed at the epi-substrate interface, which result in different structures and surfaces appearance of the defect in the epilayer. Furthermore, termination of the carrot defect inside the epilayer and the influence of substrate surface damage and growth conditions on the density of carrot defects are studied.     

A study of retention characteristics by functional group analysis using supercritical fluid chromatography

Summary Supercritical fluid chromatography (SFC) has recently been applied to the analysis of agricultural compounds. Studies investigating factors governing retention behavior of the compounds of interest will facilitate SFC method development for new compounds and metabolites. In this study, several compounds containing various functional groups were examined. Initial trends in retention were established; where appropriate, retention behavior was correlated with functional group similarities, differences and regio chemistry of compounds containing the same functional groups. Packed and capillary column SFC were used in these analyses. Results were compared to retention behavior observed under reversed-phase HPLC conditions. In general, the normal phase characteristics of SFC are very desirable in the separation of more polar compounds and metabolites of the agricultural products. Regio chemical effects and additions of methyl, phenyl, nitro, amide, carboxamide, chloro and other functional groups to common base molecules are discussed.

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Untersuchung des Retentionsverhaltens durch Analyse funktioneller Gruppen mit Hilfe der Chromatographie mit überkritischen fluiden Phasen

     

A fluorescent assay for chloride transport; identification of a synthetic anionophore with improved activity

A fluorescent assay based on the chloride-sensitive probe, lucigenin, is developed for monitoring chloride transport into vesicles, and used to compare the effectiveness of three steroid-derived transporters.     

Poly(vinylpyrrolidone)‐stabilized silver nanoparticles for strained‐silicon surface enhanced Raman spectroscopy

Poly(vinylpyrrolidone)‐stabilized silver nanoparticles deposited onto strained‐silicon layers grown on graded Si_1−xGe_x virtual substrates are utilized for selective amplification of the Si–Si vibration mode of strained silicon via surface‐enhanced Raman scattering spectroscopy. This solution‐based technique allows rapid, highly sensitive and accurate characterization of strained silicon whose Raman signal would usually be overshadowed by the underlying bulk SiGe Raman spectra. The analysis was performed on strained silicon samples of thickness 9, 17.5 and 42 nm using a 488 nm Ar⁺ micro‐Raman excitation source. The quantitative determination of strained‐silicon enhancement factors was also made. Copyright © 2011 John Wiley & Sons, Ltd.     

Structure-activity relationships in cholapod anion carriers: enhanced transmembrane chloride transport through substituent tuning

Chloride transport by a series of steroid-based "cholapod" receptors/carriers was studied in vesicles. The principal method involved preincorporation of the cholapods in the vesicle membranes, and the use of lucigenin fluorescence quenching to detect inward-transported Cl-. The results showed a partial correlation between anion affinity and transport activity, in that changes at the steroidal 7 and 12 positions affected both properties in concert. However, changes at the steroidal 3-position yielded irregular effects. Among the new steroids investigated the bis-p-nitrophenylthiourea 3 showed unprecedented activity, giving measurable transport through membranes with a transporter/lipid ratio of 1:250 000 (an average of <2 transporter molecules per vesicle). Increasing transporter lipophilicity had no effect, and positively charged steroids had low activity. The p-nitrophenyl monourea 25 showed modest but significant activity. Measurements using a second method, requiring the addition of transporters to preformed vesicle suspensions, implied that transporter delivery was problematic in some cases. A series of measurements employing membranes of different thicknesses provided further evidence that the cholapods act as mobile anion carriers.     

Dislocations and dislocation reduction in space grown GaSb

The behaviour of dislocations in GaSb crystals grown in space both from a stoichiometric melt (floating zone method, FZ) and a Bi solution (floating solution zone, FSZ) respectively, is studied. Predominantly straight 60° dislocations with Burgers vectors of the type b = a/2 <110> in (111) glide planes are identified. In the 20 mm long FZ single crystal the linear growing out of the dislocations is observed which reduces the dislocation density in the centre of the crystal to values below 300 cm^–2. The Bi incorporation in the FSZ crystal results in a misfit between seed and grown crystal and in a network of misfit dislocations at the interface. Thermocapillary convection during growth as well as the surface tension may be the reasons for the presence of curved dislocations and the higher dislocation density within a 1 – 2 mm border region at the edges of both of the crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies of iron(II) and iron(III) complexes with fac-N2O, cis-N2O2 and N2O3 donor ligands: models for the 2-His 1-carboxylate motif of non-heme iron monooxygenases

Enzymes in the oxygen-activating class of mononuclear non-heme iron oxygenases (MNOs) contain a highly conserved iron center facially ligated by two histidine nitrogen atoms and one carboxylate oxygen atom that leave one face of the metal center (three binding sites) open for coordination to cofactor, substrate, and/or dioxygen. A comparative family of [Fe(II/III)(N(2)O(n))(L)(4-n))](±x), n = 1-3, L = solvent or Cl(-), model complexes, based on a ligand series that supports a facially ligated N,N,O core that is then modified to contain either one or two additional carboxylate chelate arms, has been structurally and spectroscopically characterized. EPR studies demonstrate that the high-spin d(5) Fe(III)g = 4.3 signal becomes more symmetrical as the number of carboxylate ligands decreases across the series Fe(N(2)O(3)), Fe(N(2)O(2)), and Fe(N(2)O(1)), reflecting an increase in the E/D strain of these complexes as the number of exchangeable/solvent coordination sites increases, paralleling the enhanced distribution of electronic structures that contribute to the spectral line shape. The observed systematic variations in the Fe(II)-Fe(III) oxidation-reduction potentials illustrate the fundamental influence of differential carboxylate ligation. The trend towards lower reduction potential for the iron center across the [Fe(III)(N(2)O(1))Cl(3)](-), [Fe(III)(N(2)O(2))Cl(2)](-) and [Fe(III)(N(2)O(3))Cl](-) series is consistent with replacement of the chloride anions with the more strongly donating anionic O-donor carboxylate ligands that are expected to stabilize the oxidized ferric state. This electrochemical trend parallels the observed dioxygen sensitivity of the three ferrous complexes (Fe(II)(N(2)O(1)) < Fe(II)(N(2)O(2)) < Fe(II)(N(2)O(3))), which form μ-oxo bridged ferric species upon exposure to air or oxygen atom donor (OAD) molecules. The observed oxygen sensitivity is particularly interesting and discussed in the context of α-ketoglutarate-dependent MNO enzyme mechanisms.     

Impedance study of polymethyl methacrylate composites/multi-walled carbon nanotubes (PMMA/MWCNTs)

The dielectric behavior of polymethyl methacrylate/multi-walled carbon nanocomposites (PMMA/MWCNTs) was investigated using impedance spectroscopy technique. The composites were prepared using melt mixing with MWCNTs loading ranging from 0.01 to 10 wt%. The experimental results showed that the measured impedance reflects the insulating behavior of the host material (PMMA) with no appreciable effects of the filler less than 8.5 wt%. However, for the sample containing 10 wt%, the calculated value of dc conductivity increases with increasing temperature from 2.0×10⁻⁶ (Ω m)⁻¹ to attain a value of 4.8×10⁻⁶ (Ω m)⁻¹ at 110 °C. The percolation threshold derived from the dielectric data was estimated to be higher than 8.5 wt% and lower than 10 wt%. A temperature dependent electrical relaxation phenomenon was only observed in the sample containing 10 wt% of MWCNTs. The frequency dependence of the ac conductivity data followed a power law.