The perchlorate anion (ClO
4–
) is an anthropogenic contaminant of increasing concern in water supplies, and has been shown to disrupt thyroid activity. Most perchlorate analyses are currently carried out by ion chromatography (IC) with suppressed conductivity detection (SCD). While this procedure has been demonstrated to provide acceptable performance for analysis of water samples, the determination of perchlorate in high-conductivity aqueous extracts of plant or animal material is not readily accomplished by IC-SCD unless lengthy cleanup protocols are applied. With the addition of electrospray ionization mass spectrometry (ESI-MS) to IC, it was hypothesized that the interference imposed by various ionic species could be significantly reduced without the need for purification; however, the analysis of perchlorate in relatively unpurified extracts of biologically derived homogenates by IC-ESI-MS has not previously been described in the literature. The research presented here represents a comparison of the capabilities of IC-SCD and IC-ESI-MS to detect perchlorate in reagent water and in crude extracts of perchlorate-exposed fish (threespine stickleback, Gasterosteus aculeatus). ESI-MS was found to compare favorably to SCD for the detection of perchlorate in deionized water, and to exceed SCD performance in perchlorate analysis of fish-derived extracts. 相似文献
A method for the complete peptide mapping of the model integral membrane protein bacteri-orhodopsin is demonstrated. Utilizing more effective enzymatic digestion, procedures with capillary liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) and tandem mass spectrometry (MS/MS), all predicted tryptic digestion products were detected, as well as peptides from all previously reported post-translational modifications of bacteriorhodopsin. A significant contribution of chymotryptic-like digestion products was also observed. A characterization of the behavior of hydrophobic integral membrane peptides in a reversed-phase liquid chromatographic separation is also provided. The method reported here offers improved compatibility of the solubilizing reagents with both the chromatography and mass spectrometry, rendering it suitable for high-throughput proteomic applications. 相似文献
Studies of two distinct classes of chromium(III) cage complexes are discussed. The first are compact oxo- and carboxylate cages, made by heating precursors to high temperature under a flow of nitrogen. One of these cages, [Cr12O9(OH)3(O2CCMe3)15], has an S = 6 spin ground state which proves a very interesting subject for study by EPR and MCD spectroscopy. Use of other carboxylates leads to other octa- and dodeca-nuclear complexes. The second class of compounds are homo- and hetero-metallic wheels and chains bridged by fluoride and carboxylates. These include the first heterometallic anti-ferromagnetically coupled ring systems and are being widely studied in areas as diverse as magnetic cooling and quantum information processing. The mechanism by which these unusual cyclic and acyclic structures form is discussed. 相似文献
A combined chemical and biological process for the recycling of flue gas desulfurization (FGD) gypsum into calcium carbonate and elemental sulfur is demonstrated. In this process, a mixed culture of sulfate-reducing bacteria (SRB) utilizes inexpensive carbon sources, such as sewage digest or synthesis gas, to reduce FGD gypsum to hydrogen sulfide. The sulfide is then oxidized to elemental sulfur via reaction with ferric sulfate, and accumulating calcium ions are precipitated as calcium carbonate using carbon dioxide. Employing anaerobically digested municipal sewage sludge (AD-MSS) medium as a carbon source, SRBs in serum bottles demonstrated an FGD gypsum reduction rate of 8 mg/L/h (109 cells)-1. A chemostat with continuous addition of both AD-MSS media and gypsum exhibited sulfate reduction rates as high as 1.3 kg FGD gypsum/m3d. The increased biocatalyst density afforded by cell immobilization in a columnar reactor allowed a productivity of 152 mg SO4-2/Lh or 6.6 kg FGD gypsum/m3d. Both reactors demonstrated 100% conversion of sulfate, with 75–100% recovery of elemental sulfur and chemical oxygen demand utilization as high as 70%. Calcium carbonate was recovered from the reactor effluent on precipitation using carbon dioxide. It was demonstrated that SRBs may also use synthesis gas (CO, H2, and CO2 in the reduction of gypsum, further decreasing process costs. The formation of two marketable products—elemental sulfur and calcium carbonate—from FGD gypsum sludge, combined with the use of a low-cost carbon source and further improvements in reactor design, promises to offer an attractive alternative to the landfilling of FGD gypsum.
A molecular level understanding of the photoreactivity of self-assembled monolayers (SAMs) becomes increasingly important as the spatial resolution starts to be limited by the size of the resist and the spatial extent of the photochemical reactions in photoresist micropatterning. To this end, a number of surface characterization techniques were combined to understand the reactive agents, reactive sites, kinetics, and reaction pathways in the UV photoreactivity of octadecylsiloxane (ODS) SAMs. Quantitative analysis of our results provides evidence that ground state atomic oxygen is the primary reactive agent for the UV degradation of ODS SAMs. UV degradation, which follows zero-order kinetics, results in the scission of alkyl chains instead of the siloxane headgroups. Our results suggest that the top of the ODS SAMs is the preferential reactive site. Using a novel, highly surface sensitive technique, fluorescence labeling of surface species, we identified the presence of submonolayer quantities chemical functional groups formed by the UV degradation. These groups are intermediates in a proposed mechanism based on hydrogen abstraction. 相似文献
A simple analysis of the competition between the alternative channels of atom and excitation transfer in collisions of metastable rare-gas atoms with halogens is presented. The intervention of potential surfaces correlating with highly excited Rydberg states lying just below the limit of the molecular cation as well as those which correlate with the anion provides a qualitative rationale for much current experimental data. 相似文献
Thin film technology takes more and more importance in the development of biomedical devices dedicated to functional neurostimulation. Our research about the design of implant neurostimulating electrode is oriented toward thin film cuff electrodes based on a polyimide substrate covered by a chromium/gold/Pt film. The chromium/gold sputtered film serves as adhesion layer and current collector whereas platinum acts as an electrochemical actuator. The electrode surface has been designed to obey safe stimulation criteria (i.e. chemically inert noble metal, low electrode-electrolyte impedance, high electrochemical reversibility, high corrosion stability). The electrochemical behaviour of such platinum electrodes has been assessed and compared to a foil of platinum. Extensive in vitro characterisations of the both electrode types were carried out using AFM, SEM and electrochemical techniques. The role of enhanced surface roughness enabling high double layer capacitances to be achieved was clearly highlighted. The obtained results are discussed, with particular reference to thin film electrodes stability under in vitro electrical stimulation in NaCl 0.9% (physiological serum). Therefore, these thin film devices showed reversible PtOH formation and decomposition making them potentially attractive for the fabrication of implant stimulation cuff electrodes. 相似文献
Upon reduction with alkali metals, single-wall carbon nanotubes (SWNTS) are shown to form polyelectrolyte salts that are soluble in polar organic solvents without any sonication, use of surfactants, or functionalization whatsoever, thus forming true thermodynamically stable solutions of naked SWNTs. 相似文献
Anthanthrene (1) derivatives substituted at the 4,10 and 6,12 positions (2-6) were synthesized as promising candidates for organic light emitting diodes (OLEDs). The emission of these compounds can be manipulated in the blue region (lambda(max) = 437-467 nm) through structural modifications. Photophysical and electrochemical properties (phi(F) = 0.20-0.47; tau(F) = 2.97-6.06 ns; HOMO-LUMO energy gap = 2.25-2.56 eV) as well as geometry optimized structures of 1-6 are reported. 相似文献