Showing papers on "Atmospheric-pressure chemical ionization published in 1984"

Resonant two-photon ionization spectroscopy in supersonic beams for discrimination of disubstituted benzenes in mass spectrometry

Abstract: Supersonic molecular beam spectroscopy has great potential for selectivity in chemical analysis. In this work we have used resonant two-photon ionization (R2PI) spectroscopy in supersonic beams of argon as a means of obtaining ultraviolet ionization spectra with sharp features for unique identification of species in a mixture. This technique, therefore, provides a wavelength-selective means of forming ions for detection in time-of-flight mass spectrometry. The spectroscopy of several disubstituted benzenes including p-cresol, p-toluidine, p-aminophenol, p-fluoroaniline, p-fluorophenol, and hydroquinone has been studied near their origin transitions. These molecules have low quantum yields in fluorescence but can be detected with great sensitivity (< 20 ppb) by using laser ionization. On the basis of the separation between spectral lines of compounds in various mixtures, we estimate the combined maximum discrimination possible in a mass spectrometer, thus demonstrating the capability of this technique for identification. When this method is used, an experimental discrimination between p-cresol and p-fluoroaniline on the order of 1:5000 can in principle be obtained.

Differentiation of polycyclic aromatic hydrocarbons using electron capture negative chemical ionization

Abstract: A number of isomeric polycyclic aromatic hydrocarbons may be distinguished using electron capture negative chemical ionization when methane is used as a buffer gas, including benzo[a]pyrene and benzo[e]pyrene. The ionization behavior of these compounds may be predicted, on the basis of their electron afinities, allowing compounds to be distinguished without the use of standards.

Chemical ionization–fast-atom bombardment mass spectrometry: a novel ionization method

Abstract: Chemical ionization reactions have been used with fast-atom bombardment mass spectrometry technique to post-ionize desorbed neutral species by proton transfer, charge exchange, and association reactions in order to enhance molecular parent ions.

Mass spectral characterization of oxygen-containing aromatics with methanol chemical ionization

Abstract: Chemical ionization mass spectrometry with methanol and deuterated methanol as ionization reagents is used to differentiate oxygen-containing aromatics, including phenols, aromatic ethers, and aromatic substituted alcohols, as well as compounds containing more than one oxygen atom. The analogous sulfur-containing aromatics may be similarly differentiated. Methanol chemical ionization is used to characterize a neutral aromatic polar subfraction of a coal-derived liquid by combined gas chromatography/mass spectrometry. 16 references, 2 tables, 1 figure.

Materials Characterization Using Thermogravimetry Coupled to Triple Quadrupole Tandem Mass Spectrometry (MS/MS)

Abstract: Thermogravimetric analysis (TGA) coupled with sequential mass spectrometry (MS/MS) offers unambiguous structural identification of compounds evolving during thermo-degradative processes without interrupting the TGA-mass spectrometer analytical procedure. MS/MS identification of co-evolving compounds, combined with the weight-loss data obtained from TGA, furnishes a means of delineating complex thermolytic pathways. The compatibility of TGA (an atmospheric pressure technique) with Atmospheric Pressure Chemical Ionization (APCI), as offered on the TAGA® 6000 MS/MS system, permits an interface which is easily coupled and decoupled making the system “user-friendly” and well suited to routine quality control and trouble-shooting applications.

Atmospheric pressure ionization mass spectrometry of the polychlorinated dibenzo-p-dioxins

Abstract: The branching ratios for the reaction pathways of 39 polychlorinate dibenzo-p-dioxins (PCDDs) under oxygen negative chemical ionization/atmospheric pressure ionization mass spectrometric conditions were measured. These results demonstrated that the PCDDs could be separated into 14 groups by this technique. These results were compared with those reported previously for 14 PCDDs using oxygen negative chemical ionization mass spectrometry.

Analysis of Middle Distillate Fuels by High Resolution Field Ionization Mass Spectrometry.

Abstract: : A method for the rapid and detailed chemical characterization of distillate fuels has been developed using high resolution field ionziation mass spectrometric (HR-FIMS) techniques. A vintage AEI MS-9 mass spectrometer has been modified to house a volcano-style field ionizer and has been equipped with a high-temperature batch inlet system. Field ionization is particularly useful in this regard because it produces only molecular ions for most compounds and because different compound types do not differ in their ionization efficiencies by more than a factor of four. The mass spectrometer is operated at a resolution of 3000, which is adequate to resolve all the different types of hydrocarbons likely to be present in the fuel sample. Software has been written to present the mass spectrum intensities in a matrix where the various columns represent the different z-series of the hydrocarbons and the rows represent the number of carbon atoms in any given component. Analysis of a stable and an unstable jet fuel showed that the unstable fuel had a substantially higher naphthalene content.

Mass Spectra of Nickel Complexes measured by Liquid Ionization Mass Spectrometry

Abstract: Nickel halide complexes containing ethylenediamines as ligands were examined by liquid ionization mass spectrometry. Protonated molecules obtained as the base peaks and their isotope ratios agreed with their natural abundances. The mass spectra corresponding well to the structure of the complexes were better than their FD and FAB spectra.

Chemical ionization mass spectra of derivatized 1‐benzyltetrahydroisoquinoline alkaloids

Abstract: A study of the chemical ionization mass spectral characteristics of a series of derivatized 1-benzyltetrahy-droisoquinoline alkaloids is presented. Tetrahydropapaveroline and some related benzyltetrahydroisoquinolines were converted to their corresponding O-trimethylsilyl of N-trifluoroacetyl-O-trimethylsilyl derivatives prior to analysis by combined gas chromatographic methane chemical ionization mass spectrometry. The chemical ionization mass spectra of the derivatized alkaloids are compared to the electron impact mass spectra of the N-trifluoroacetyl-O-trimethylsilyl derivative of tetrahydropapaveroline, a representative benzyltetrahydroisoquinoline alkaloid. The effects of the nitrogen substituent and ion source pressure on the relative abundance of significant ions in the chemical ionization mass spectra of these alkaloids are also described.