The Experts below are selected from a list of 50274 Experts worldwide ranked by ideXlab platform
Gary M Hieftje - One of the best experts on this subject based on the ideXlab platform.
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atmospheric pressure Chemical Ionization source 1 Ionization of compounds in the gas phase
Analytical Chemistry, 2008Co-Authors: Francisco J Andrade, Jacob T Shelley, William C Wetzel, Michael R Webb, Gerardo Gamez, Steven J Ray, Gary M HieftjeAbstract:A novel Chemical Ionization source for organic mass spectrometry is introduced. This new source uses a glow discharge in the flowing afterglow mode for the generation of excited species and ions. T...
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atmospheric pressure Chemical Ionization source 1 Ionization of compounds in the gas phase
Analytical Chemistry, 2008Co-Authors: Francisco J Andrade, Jacob T Shelley, William C Wetzel, Michael R Webb, Gerardo Gamez, Steven J Ray, Gary M HieftjeAbstract:A novel Chemical Ionization source for organic mass spectrometry is introduced. This new source uses a glow discharge in the flowing afterglow mode for the generation of excited species and ions. The direct-current gas discharge is operated in helium at atmospheric pressure; typical operating voltages and currents are around 500 V and 25 mA, respectively. The species generated by this atmospheric pressure glow discharge are mixed with ambient air to generate reagent ions (mostly ionized water clusters and NO+), which are then used for the Ionization of gaseous organic compounds. A wide variety of substances, both polar and nonpolar, can be ionized. The resulting mass spectra generally show the parent molecular ion (M+ or MH+) with little or no fragmentation. Proton transfer from ionized water clusters has been identified as the main Ionization pathway. However, the presence of radical molecular ions (M+) for some compounds indicates that other Ionization mechanisms are also involved. The analytical capabi...
Michael Spiteller - One of the best experts on this subject based on the ideXlab platform.
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determination of selected sulfonamide antibiotics and trimethoprim in manure by electrospray and atmospheric pressure Chemical Ionization tandem mass spectrometry
Rapid Communications in Mass Spectrometry, 2002Co-Authors: Thomas Pfeifer, Jochen Tuerk, Kai Bester, Michael SpitellerAbstract:A method for the determination of sulfonamides and trimethoprim in the complex matrix liquid manure has been developed using reversed-phase liquid chromatography and atmospheric pressure Chemical Ionization (APCI) tandem mass spectrometry. A comparison was made between electrospray and atmospheric pressure Chemical Ionization. APCI proved to be more robust and less sensitive to matrix effects. High-performance liquid chromatographic (HPLC) separation of the analytes was achieved in less than 7 min. The compounds were extracted with ethyl acetate and the extracts were cleaned up by solid-phase extraction on an aminopropyl column. Recoveries were not dependent on the concentration level. The mean recoveries were as follows: trimethoprim 79.0%, sulfadiazine 80.5%, N4-acetylsulfadiazine 91.0%, sulfamerazine 78.6%, sulfadimidine 77.2% and sulfamethoxazole 82.8%. Linearity was established over a concentration range of 5 to 5000 µg/kg with correlation coefficients greater than 0.99. The method had a limit of quantitation (LOQ) of 5 µg/kg manure. Copyright © 2002 John Wiley & Sons, Ltd.
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determination of selected sulfonamide antibiotics and trimethoprim in manure by electrospray and atmospheric pressure Chemical Ionization tandem mass spectrometry
Rapid Communications in Mass Spectrometry, 2002Co-Authors: Thomas Pfeifer, Jochen Tuerk, Kai Bester, Michael SpitellerAbstract:A method for the determination of sulfonamides and trimethoprim in the complex matrix liquid manure has been developed using reversed-phase liquid chromatography and atmospheric pressure Chemical Ionization (APCI) tandem mass spectrometry. A comparison was made between electrospray and atmospheric pressure Chemical Ionization. APCI proved to be more robust and less sensitive to matrix effects. High-performance liquid chromatographic (HPLC) separation of the analytes was achieved in less than 7 min. The compounds were extracted with ethyl acetate and the extracts were cleaned up by solid-phase extraction on an aminopropyl column. Recoveries were not dependent on the concentration level. The mean recoveries were as follows: trimethoprim 79.0%, sulfadiazine 80.5%, N(4)-acetylsulfadiazine 91.0%, sulfamerazine 78.6%, sulfadimidine 77.2% and sulfamethoxazole 82.8%. Linearity was established over a concentration range of 5 to 5000 microg/kg with correlation coefficients greater than 0.99. The method had a limit of quantitation (LOQ) of 5 microg/kg manure.
David L Hachey - One of the best experts on this subject based on the ideXlab platform.
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quantification of cholesterol tracers by gas chromatography negative ion Chemical Ionization mass spectrometry
Journal of Mass Spectrometry, 1996Co-Authors: Richard E Ostlund, Matthew S Bosner, William F Stenson, David L HacheyAbstract:Because of its high sensitivity, gas chromatography negative ion Chemical Ionization mass spectrometry (GC-NCI-MS) is a potentially valuable analytical tool for the study of cholesterol metabolism. Of several derivatives prepared for potential use in tracer studies pentafluorobenzoyl cholesterol was selected because it formed rapidly at ambient temperature and was stable for long periods, could be detected at a level of 1 fmol, and yielded a mass spectrum in which the molecular ion was the principal component. Hexadeuterated cholesterol tracer ([26,26,26,27,27,27- 2 H 6 ]cholesterol) could be detected in dilutions up to 2700 in unlabeled cholesterol by selected ion monitoring with a coefficient of variation averaging 3.2%. In seven normal subjects tracer cholesterol was infused intravenously and plasma cholesterol enrichment was determined after 4 h. The measured rapidly miscible cholesterol pool was 391.0 ± 38.6 mg cholesterol/kg. Negative ion mass spectrometry of pentafluorobenzyol cholesterol will facilitate analysis of both small amounts of natural cholesterol and labeled cholesterol in applications where sensitivity is critical.
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isotopic determination of organic keto acid pentafluorobenzyl esters in biological fluids by negative Chemical Ionization gas chromatography mass spectrometry
Analytical Chemistry, 1991Co-Authors: David L Hachey, Peter J Reeds, Bruce W. Patterson, Louis J ElsasAbstract:A rapid, single-step procedure for the extraction and derivatization of organic α-keto acids from microliter quantities of human plasma has been developed. The keto acids were analyzed as the pentafluorobenzyl (PFB) ester by methane negative Chemical Ionization gas chromatography/mass spectrometry. We have used this procedure to study leucine and 4-methyl-2-oxo-pentanoic acid metabolism by using stable isotopically labeled tracers in a variety of normal and abnormal conditions
Heikki Kallio - One of the best experts on this subject based on the ideXlab platform.
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quantification of triacylglycerol regioisomers by ultra high performance liquid chromatography and ammonia negative ion atmospheric pressure Chemical Ionization tandem mass spectrometry
Rapid Communications in Mass Spectrometry, 2010Co-Authors: Heidi Leskinen, Jukkapekka Suomela, Heikki KallioAbstract:The regioisomer composition of triacylglycerols (TAGs) in various vegetable oils was determined with a new liquid chromatography/tandem mass spectrometry (LC/MS/MS method). A direct inlet ammonia negative ion Chemical Ionization (NICI) MS/MS method was improved by adapting it to LC negative ion (NI) atmospheric pressure Chemical Ionization (APCI) MS/MS system using ammonia as nebulizer gas. The method is based on the preferential formation of [M–H–RCOOH–100]− ions during collision-induced dissociation by loss of sn-1/3 fatty acids from [M–H]− ions. Calibration curves were created from nine reference TAGs: Ala/L/L, Gla/L/L, L/L/O, L/O/O, P/O/O, P/P/O, Po/Po/V, Po/Po/O, and C/O/O. The calibration curves were used to quantify the regioisomer compositions of selected TAGs in rapeseed oil, sunflower seed oil, palm oil, black currant seed oil, and sea buckthorn pulp oil. The method discriminates the different regioisomers and the results obtained by this method were in good agreement with previous results. This proves that this new method can be used for the determination of regiospecific distribution of fatty acids in TAGs. Copyright © 2009 John Wiley & Sons, Ltd.
Marcos N Eberlin - One of the best experts on this subject based on the ideXlab platform.
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assessing relative electrospray Ionization atmospheric pressure photoIonization atmospheric pressure Chemical Ionization and atmospheric pressure photo and Chemical Ionization efficiencies in mass spectrometry petroleomic analysis via pools and pairs of selected polar compound standards
Energy & Fuels, 2016Co-Authors: Marcos A Pudenzi, Marcos N EberlinAbstract:A total of 15 standard compounds with structures similar to those normally found in crude oils were analyzed using an ultrahigh-resolution and high-accuracy Fourier transform ion cyclotron resonance (7.2 T LTQ FT Ultra, Thermo Fisher, Bremen, Germany) mass spectrometer. Four different Ionization techniques were used: electrospray Ionization (ESI), atmospheric pressure Chemical Ionization (APCI), atmospheric pressure photoIonization (APPI), and a novel technique that couples APCI and APPI, herein termed atmospheric pressure photo- and Chemical Ionization (APPCI). Relationships between Chemical structures and Ionization efficiencies were established for these techniques, which operate via different Ionization mechanisms. The unsaturation level and position of the double bond were shown to be key factors on Ionization efficiency for all Ionization techniques. Comparisons between molecules with similar backbones but with different heteroatoms were also made. For the whole mixture, APPI showed the highest sens...
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probing the mechanism of the petasis olefination reaction by atmospheric pressure Chemical Ionization mass and tandem mass spectrometry
Organic Letters, 2003Co-Authors: Eduardo C Meurer, Leonardo S Santos, Ronaldo A Pilli, Marcos N EberlinAbstract:Atmospheric pressure Chemical Ionization mass (APCI-MS) and tandem mass spectrometry (APCI-MS/MS) is used to probe the mechanism of the Petasis olefination reaction. Oxatitanacycle intermediates 4 were transferred from solution to the gas phase, detected as 4H+ by APCI-MS with characteristic Ti-isotopic patterns, and structurally characterized by APCI-MS/MS. Detection of 4H+, which upon collision activation dissociates to both 3H+ and Cp2TiOH+, fully supports the Hughes mechanism as depicted above.