Search results for "Electron ionization"
showing 10 items of 82 documents
Critical assessment of ionization patterns and applications of ambient desorption/ionization mass spectrometry using FAPA-MS
2016
Ambient desorption/ionization mass spectrometry (MS) has gained growing interest during the last decade due to its high analytical performance and yet simplicity. Here, one of the recently developed ambient desorption/ionization MS sources, the flowing atmospheric-pressure afterglow (FAPA) source, was investigated in detail regarding background ions and typical ionization patterns in the positive as well as the negative ion mode for a variety of compound classes, comprising alkanes, alcohols, aldehydes, ketones, carboxylic acids, organic peroxides and alkaloids. A broad range of signals for adducts and losses was found, besides the usually emphasized detection of quasimolecular ions, i.e. […
A new interface to couple thin-layer chromatography with laser desorption/atmospheric pressure chemical ionization mass spectrometry for plate scanni…
2005
An interface to allow on-line qualitative and quantitative full-plate detection and analysis of compounds separated by thin-layer chromatography (TLC) is presented. A continuous wave diode laser is employed as a desorption source. Atmospheric pressure chemical ionization mass spectrometry ionizes and subsequently identifies the desorbed sample molecules. Besides direct laser desorption on untreated TLC plates, graphite particles were used as a matrix to couple in the laser power and improve the efficiency of desorption.
Comparison of gas and liquid chromatography coupled to mass spectrometry for the residue analysis of pesticides in organges
2001
Liquid chromatography-mass spectrometry (LC-MS) with atmospheric pressure chemical ionization (APCI), and gas chromatography-mass spectrometry (GC-MS) with electron impact ionization (EI), are compared for the determination of eight pesticides in oranges. Seven of the selected pesticides, chlorpyriphos, chlorpyriphos-methyl, imazalil, α and β-endosulfan, endosulfan sulphate and dicofol, are commonly determined by GC whereas one, thiabendazole, can only be directly determined by LC. Primary ions [M-H]− or [M-Cl+O]− are obtained using LC-APCI-MS in negative ionization (NI) mode. In contrast, a high degree of fragmentation is reported with GC-MS. Both techniques were applied to oranges, which …
Online atmospheric pressure chemical ionization ion trap mass spectrometry (APCI-IT-MS<sup>n</sup>) for measuring organic…
2012
Abstract. The field application of an aerosol concentrator in conjunction with an atmospheric pressure chemical ionization ion trap mass spectrometer (APCI-IT-MS) at the boreal forest station SMEAR II at Hyytiälä, Finland, is demonstrated in this study. APCI is a soft-ionization technique allowing online measurements of organic acids in the gas and particle phase. The detection limit for the acid species in the particle phase was improved by a factor of 7.5 to 11 (e.g. ∼40 ng m3 for pinonic acid) by using the miniature versatile aerosol concentration enrichment system (mVACES) upstream of the mass spectrometer. The APCI-IT-MS was calibrated in the negative ion mode with two biogenic organic…
Experimental investigations of two doubly excited NI multiplets
2005
Experimental Stark-broadening studies of two NI multiplets ( 1 D)3s 2 D - ( 1 D)3p 2 D° and ( 1 D)3s 2 D - ( 1 D) 3 p 2 F° are reported. Measurements were performed using a wall-stabilized arc operated at atmospheric pressure in helium with small amounts of nitrogen and hydrogen. The Stark broadening parameters: the electron impact width (w e ) and shift (d e ) have been determined.
Development and optimization of gas chromatography coupled to high resolution mass spectrometry based method for the sensitive determination of Dechl…
2017
An analytical method has been developed for the trace determination of 10 dechlorane-related compounds (DRCs) in food products by gas chromatography - high resolution mass spectrometry (GC-HRMS). The highest sensitivity of this instrumental analysis method was achieved by selection of the GC column type, optimization of the heated zones within the instrument, and adjusting the electron impact energy. The efficiency of solid phase extraction as clean-up procedure was also optimized. Two different types of cartridges - neutral silica gel and Florisil®, as well as seven organic solvents or their mixtures - n-hexane, cyclohexane, acetone, toluene, n-hexane/ethyl acetate, n-hexane/acetone, and n…
Resonances in the electron impact excitation of metastable states of mercury
1984
Metastable excitation of mercury by electron impact is studied at energies up to the first ionisation potential using an energy selected electron beam with an energy spread of 50 meV FWHM. A great number of resonances is observed in the excitation function. Agreement is good on the whole with a recent relativisticR-matrix calculation and with a former analysis of resonances in the elastic cross section.
Gas-Phase Vibrational Spectroscopy of the Hydrocarbon Cations l-C3H+, HC3H+, and c-C3H2+: Structures, Isomers, and the Influence of Ne-Tagging
2019
We report the first gas-phase vibrational spectra of the hydrocarbon ions C3H+ and C3H2+. The ions were produced by electron impact ionization of allene. Vibrational spectra of the mass-selected ions tagged with Ne were recorded using infrared predissociation spectroscopy in a cryogenic ion trap instrument using the intense and widely tunable radiation of a free electron laser. Comparison of high-level quantum chemical calculations and resonant depletion measurements revealed that the C3H+ ion is exclusively formed in its most stable linear isomeric form, whereas two isomers were observed for C3H2+. Bands of the energetically favored cyclic c-C3H2+ are in excellent agreement with calculated…
Untersuchungen von polymeren im massenspektrometer, 5. Fragmentierungsreaktionen oligomerer oxy- und thio-1,4-phenylene
1975
Als Modellverbindungen zur Differenzierung von thermischen und elektronenstosinduzierten Abbaureaktionen von entsprechenden Polymeren im Massenspektrometer wurden die Fragmentierungsreaktionen oligomerer 1,4-Phenylene mit Sauerstoff-, Schwefel- und Disulfidbrucken sowie eine Reihe alternierender Co-oligomersysteme untersucht. Bei verringerter Ionisationsenergie (15 eV) treten in den Massenspektren aller unzersetzt fluchtigen Oligomeren die Molekulionen als intensivste Peaks auf, so das–bei strukturell gleichen Polymeren–eine eindeutige Identifizierung von thermischen Abbauprodukten erwartet werden kann. In Abhangigkeit von den Bruckenatomen werden charakteristische Unterschiede in den Inten…
Strukturuntersuchung von polyestern durch direkten abbau im massenspektrometer, 3. Poly-β-propiolacton, poly-β-pivalolacton und poly-δ-valerolacton
1978
Poly(oxycarbonylethylene) (poly-β-propiolactone), poly(oxycarbonyl-1,1-dimeothylethylene) (poly-β-pivalolactone), and poly(oxycarbonyltetramethylene) (poly-δ-valerolactone) were pyrolyzed directly in the ion source of a mass spectrometer and their thermal and electron impact induced degradation mechanisms are established. Poly-β-propiolactone is thermally degraded by rupture of the OCH2-bond by a cis elimination to give carboxyl and acryloyl endgroups, whereas poly-δ-valerolactone depolymerizes to δ-valerolactone. Poly-β-pivalolactone degrades thermally to cyclic oligomers of pivalolactone, which could be proved by a separated pyrolysis and IR-spectroscopy and gel chromatography.