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Gradient Conditions (gradient + condition)
Selected AbstractsHigh-efficiency peptide analysis on monolithic multimode capillary columns: Pressure-assisted capillary electrochromatography/capillary electrophoresis coupled to UV and electrospray ionization-mass spectrometryELECTROPHORESIS, Issue 21 2003Alexander R. Ivanov Abstract High-efficiency peptide analysis using multimode pressure-assisted capillary electrochromatography/capillary electrophoresis (pCEC/pCE) monolithic polymeric columns and the separation of model peptide mixtures and protein digests by isocratic and gradient elution under an applied electric field with UV and electrospray ionization-mass spectrometry (ESI-MS) detection is demonstrated. Capillary multipurpose columns were prepared in silanized fused-silica capillaries of 50, 75, and 100 ,m inner diameters by thermally induced in situ copolymerization of methacrylic monomers in the presence of n -propanol and formamide as porogens and azobisisobutyronitrile as initiator. N -Ethylbutylamine was used to modify the chromatographic surface of the monolith from neutral to cationic. Monolithic columns were termed as multipurpose or multimode columns because they showed mixed modes of separation mechanisms under different conditions. Anion-exchange separation ability in the liquid chromatography (LC) mode can be determined by the cationic chromatographic surface of the monolith. At acidic pH and high voltage across the column, the monolithic stationary phase provided conditions for predominantly capillary electrophoretic migration of peptides. At basic pH and electric field across the column, enhanced chromatographic retention of peptides on monolithic capillary column made CEC mechanisms of migration responsible for separation. The role of pressure, ionic strength, pH, and organic content of the mobile phase on chromatographic performance was investigated. High efficiencies (exceeding 300,000 plates/m) of the monolithic columns for peptide separations are shown using volatile and nonvolatile, acidic and basic buffers. Good reproducibility and robustness of isocratic and gradient elution pressure-assisted CEC/CE separations were achieved for both UV and ESI-MS detection. Manipulation of the electric field and gradient conditions allowed high-throughput analysis of complex peptide mixtures. A simple design of sheathless electrospray emitter provided effective and robust low dead volume interfacing of monolithic multimode columns with ESI-MS. Gradient elution pressure-assisted mixed-mode separation CE/CEC-ESI-MS mass fingerprinting and data-dependent pCE/pCEC-ESI-MS/MS analysis of a bovine serum albumin (BSA) tryptic digest in less than 5 min yielding high sequence coverage (73%) demonstrated the potential of the method. [source] A Practical Approach to the Design, Monitoring, and Optimization of In Situ MTBE Aerobic BiobarriersGROUND WATER MONITORING & REMEDIATION, Issue 1 2010Paul C. Johnson A paradigm for the design, monitoring, and optimization of in situ methyl tert -butyl ether (MTBE) aerobic biobarriers is presented. In this technology, an oxygen-rich biologically reactive treatment zone (the "biobarrier") is established in situ and downgradient of the source of dissolved MTBE contamination in groundwater, typically gasoline-impacted soils resulting from leaks and spills at service station sites or other fuel storage and distribution facilities. The system is designed so that groundwater containing dissolved MTBE flows to, and through, the biobarrier treatment zone, ideally under natural gradient conditions so that no pumping is necessary. As the groundwater passes through the biobarrier, the MTBE is converted by microorganisms to innocuous by-products. The system also reduces concentrations of other aerobically degradable chemicals dissolved in the groundwater, such as benzene, toluene, xylenes, and tert -butyl alcohol. This design paradigm is based on experience gained while designing, monitoring, and optimizing pilot-scale and full-scale MTBE biobarrier systems. It is largely empirically based, although the design approach does rely on simple engineering calculations. The paradigm emphasizes gas injection,based oxygen delivery schemes, although many of the steps would be common to other methods of delivering oxygen to aquifers. [source] Tomography of temperature gradient metamorphism of snow and associated changes in heat conductivityHYDROLOGICAL PROCESSES, Issue 18 2004Martin Schneebeli Abstract Temperature gradient metamorphism is one of the dominant processes changing the structure of natural dry snow. The structure of snow regulates the thermal and mechanical properties. Physical models and numerical simulations of the evolution of the snow cover require a thorough understanding of the interplay between structure and physical properties. The structure of snow and the heat conductivity were measured simultaneously without disturbance in a miniature snow breeder. The structure was measured by microtomography, and heat conductivity by measuring heat fluxes and temperatures. A temperature gradient from 25 to 100 K m,1 was applied to the snow. The snow density range of the samples varied from 150 to 500 kg m,3. The density in the observed volume remained constant during the experiments under temperature gradient conditions. The structure was analysed with respect to the size of typical ice structures and air pores, specific surface area, curvature and anisotropy of the ice matrix. The temporal changes in structure and heat conductivity are compared. The heat conductivity changed by as much as twice its initial value, caused by changes in structure and texture, but not due to changes in density. This shows the enormous importance of structure in the evolution of the heat conductivity. The observed changes are not in good agreement with the current understanding of the metamorphic process, because heat conductivity increased during temperature gradient metamorphism, instead of the expected decrease due to a shrinking of the bonds. We also observed a plateau in the evolution of the heat conductivity coefficient, which indicates a quasi-steady state of the structural evolution with respect to thermophysical properties of snow. Copyright © 2004 John Wiley & Sons, Ltd. [source] Temperature-Gradient Effects in Thermal Barrier Coatings: An Investigation Through Modeling, High Heat Flux Test, and Embedded SensorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Yang Tan The harsh thermal environment in gas turbines, including elevated temperatures and high heat fluxes, induces significant thermal gradients in ceramic thermal barrier coatings (TBCs), which are used to protect metallic components. However, the thermal conductivity of plasma-sprayed TBC increases with exposure at high temperatures mainly due to sintering phenomena and possible phase transformation, resulting in coating performance degradation and potential thermal runaway issues. An analytical thermal model and experimentally obtained coating thermal conductivity data are used to determine the coating through-thickness temperature profile and effective thermal conductivity under gradient conditions at high temperatures. High heat flux tests are then performed on TBCs to evaluate coating thermal behavior under temperature gradients close to service conditions. Coating internal temperature during the tests was also measured by thermally sprayed embedded thermocouples within the top coat. This combined approach provides a sintering map with a new model and allows for the assessment of temperature-gradient effects on the thermal performance of plasma-sprayed TBCs. [source] Semi-automated quantification of ivermectin in rat and human plasma using protein precipitation and filtration with liquid chromatography/tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2004Tony Pereira Ivermectin is a parasiticide commonly used in humans and livestock. It is currently under development for the treatment of pediculosis of humans (head lice) that does not respond to established treatments. A liquid chromatography/turbo ion spray tandem mass spectrometry (LC/TIS-MS/MS) method for the determination of ivermectin in rat and human plasma has been developed that uses emamectin [4,-epi-(methylamino)-4,-deoxyavermectin] as the internal standard. Sample preparation involved protein precipitation and filtration of fortified plasma in the 96-well format. Chromatographic separation was accomplished using fast gradient conditions on a C8 stationary phase. The analytes were detected with the mass spectrometer operated in the positive ion, multiple reaction monitoring mode. The method exhibited good intra- and interday accuracy and precision, and was linear over a dynamic range of 1,2000,ng/mL. In rat plasma, intraday accuracy ranged between 84,93% for the low quality control (QC) sample (1.5 ng/mL), and between 91,109% for the remaining QCs. Intraday precision ranged between 4.9,15% for the low QC, and 0.8,6.3% for the remaining QCs. Interday accuracy ranged between 88,107%, and precision between 4.1,11%. Similar data was obtained using human plasma. An investigation of matrix effects indicated that the ionization efficiency of ivermectin was favored by the presence of an ammonium ion in an aqueous environment. The implications of this observation toward assay sensitivity are discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Simultaneous determination of estramustine phosphate and its four metabolites in human plasma by liquid chromatography,ionspray mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 5 2004M. Breda Abstract A sensitive and selective method, using liquid chromatography,ionspray mass spectrometry, was developed and validated for the simultaneous determination of Estracyt (estramustine phosphate) and its four metabolites, estramustine, estromustine, estrone and estradiol, in human plasma. Deuterated internal standards were available for all analytes. The ,ve compounds were extracted from plasma by protein precipitation with acetonitrile. The chromatographic separation was performed using a Zorbax SB C18, (150 × 4.6 mm i.d., 5 µm) reversed-phase column under gradient conditions with a mobile phase containing 2 mm ammonium acetate buffer (pH 6.8) and acetonitrile. MS detection was by electrospray ionization with multiple reaction monitoring in the positive ion mode for estramustine phosphate, estromustine and estramustine, and in the negative ion mode for estrone and estradiol. The limit of quantitation was 10 ng/mL for estramustine phosphate, 3 ng/mL for estromustine, estramustine and estrone and 30 ng/mL for estradiol. Linearity was veri,ed from these LLOQs up to about 4000 ng/mL for the parent drug and 2000 ng/mL for the metabolites. Inter-day precision and accuracy values were all less than 15%. This assay was applied successfully to the routine analysis of human plasma samples collected in cancer patients administered estramustine phosphate intravenously. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||