Showing papers on "Atmospheric-pressure chemical ionization published in 1986"

Capillary column ammonia chemical ionization mass spectrometry of organophosphorus chemical warfare agents and simulants

Abstract: Capillary column ammonia chemical ionization mass spectrometry was investigated as a technique for the characterization of a number of organophosphorus chemical warfare agents and simulants, since electron impact ionization provides little or no molecular ion information for these compounds. The effects of source temperature, source pressure, electron energy and electron emission were investigated in order to optimize ammonia chemical ionization conditions. Source temperature was found to have a dramatic effect on the chemical ionization mass spectra acquired. Abundant [M + NH4]+ and/or [M + H]+ quasimolecular ions were usually observed at lower source temperatures for the selected compounds under positive ion chemical ionization conditions, along with a number of characteristic fragmentation ions. Full-scan mass spectra were obtained for 1--2 ng of analyte during the capillary column ammonia chemical ionization operation. The sensitivity, molecular ion information afforded and lack of background interference ions associated with this technique make it a good candidate for the confirmation of organophosphorus chemical warfare agents and simulants.

Ammonia and methane chemical ionization mass spectra of acid and carbamate pesticides using direct supercritical fluid injection

Abstract: The ammonia and methane chemical ionization mass spectra of several carbamate and acid pesticides were obtained utilizing capillary supercritical fluid chromatography (SFC) for introduction. These compounds are generally not amenable to gas chromatography and the supercritical fluid method allows low-temperature separations (using carbon dioxide or nitrous oxide as mobile phases) with highly selective chemical ionization mass spectrometric detection for analysis. Ionization with ammonia produces primarily ammonium adduct ions, [M + 18]+, and protonated molecules, [M + 1]+, for all compounds. More energetic methane chemical ionization produces spectra containing fragment ions characteristic of the pesticide structure. All compounds were analysed under similar chromatographic conditions, with optimization for individual compounds minimized, and detection limits were in the picogram range. Analysis time for all compounds was under five minutes and no mobile phase interferences or thermal degradation was noted.

Stereochemical effects in mass spectrometry. 3—Detection of chirality by chemical ionization mass spectrometry

Abstract: It was found that the chemical ionization mass spectra of the enantiomers of some α-amino acids and α-hydroxy acids could be definitely distinguished when a chiral compound, l-amyl alcohol, was used as a component of the reagent gases. The relative abundances of some characteristic ions produced through ion-molecule reactions in the gas phase were much higher in the D isomers than in the L isomers. The results were highly reproducible. This approach proved to be a convenient way for the detection of the chirality of these compounds by chemical ionization mass spectrometry.

Mass spectral investigations on trichothecene mycotoxins. I. Application of negative ion chemical ionization techniques for the simultaneous and accurate analysis of simple trichothecenes in picogram levels.

Abstract: A fast and sensitive gas chromatographic/negative ion chemical ionization mass spectrometric method for the simultaneous detection and quantification of several simple trichothecene mycotoxins and related molecules with good precision has been developed. The method consists of the conversion of the polar trichothecenes into their volatile and stable heptafluorobutyryl esters, followed by gas chromatographic/mass spectrometric analysis of the derivatives. The derivatives were ionized under chemical ionization conditions and the negative ions were monitored. The samples were screened for the presence of trichothecenes by monitoring one characteristic ion by selected ion monitoring for each analyte. The detected compounds were confirmed by monitoring 5-6 characteristic ions by selected ion monitoring whenever the amount of analyte present was insufficient to obtain a full scan negative ion chemical ionization mass spectrum. Two semi-synthetic trichothecenes, 4-deoxyverrucarol and 16-hydroxyverrucarol, were investigated and found to be adequate internal standards both for detection and quantification of these toxic compounds. Femtogram and low picogram (1-5 pg) quantities of these compounds could be detected and confirmed, respectively, by this procedure. A short clean-up procedure using Sep-Pak (silica gel) cartridges was developed and found to be applicable for the analysis of some real samples. Several spiked and real samples were analysed by this method, with excellent sensitivity and precision.

Mass spectrometry with photoionization of n-alkanes, alcohols, ketones, esters, and amines at atmospheric pressure

Abstract: 1. The possibility of obtaining only one ion in the mass spectra was demonstrated in conditions of ionization with UV radiation at atmospheric pressure: the M+ ion for n-alkanes and the MH+ ion for alcohols, ketones, esters, and amines. 2. Ionization with UV radiation at atmospheric pressure permits broadening the linear range by 104–106 times and decreasing the limit of detection ∼102 times in comparison to the existing methods of mass spectral analysis with ionization at atmospheric pressure and by 102–104 and 102 times in comparison to chemical ionization in comparable conditions. 3. The possibility of mass spectrometric analysis of submicrogram quantities of the components of mixtures without preliminary separation was demonstrated on the example of n-alkanes and aromatic hydrocarbons in conditions of ionization with UV radiation.

Substituent effects in charge exchange chemical ionization mass spectrometry

Abstract: Substituent effects in charge exchange chemical ionization mass spectrometry are examined. A linear Hammett relationship was observed for a series of monosubstituted benzenes and naphthalenes. Substituted aromatic compounds not distinguished by electron impact mass spectrometry can be predictively resolved by charge exchange chemical ionization mass spectrometry.

Negative ion atmospheric pressure ionization mass spectrometry: Ionization of aromatic hydrocarbons

Abstract: A corona discharge atmospheric pressure ionization source generates the reagent ions, OH− and O− ions in addition to better known O2− ions, when ambient air is used as the carrier. All three ions are gas-phase bases that could form negative ions from organics via proton abstraction. Ionization of simple aromatic hydrocarbons by O2− is thermodynamically not feasible. Simple aromatic hydrocarbons are ionized only by O− and/or OH− to form [M H]− ions. However, [M H]− ions do not appear in the mass spectrum as they undergo stabilization via clustering with predominantly oxygen atoms.

Methane negative ion chemical ionization fragmentation processes of deuterated analogues of Ortho-, meta- and para-tyramine-N,O-dipentafluoropropionate derivatives

Abstract: The methane negative ion chemical ionization (NICI) mass spectra of the three isomeric tyramine-N-O-dipentafluoropropionate derivatives are unique insofar as each has a different base peak in contrast to their methane positive ion chemical ionization (PICI) mass spectra which are very similar in appearance. Deuterium-labelling studies in the three isomeric tyramine derivatives have elucidated the fragmentation processes accompanying the electron capture NICI process for each derivatized compound.

Tgaiapciimsims, A New Technique For The Study Of Pyrolysis And Combustion Products

Abstract: The Fire Research Section, Division of Building Research, National Research Council of Canada has acquired a SCIEX TAGA 6000 APCI (atmospheric pressure chemical ionization)/MS/MS, an analytical instrument unique for its high sensitivity and high speed in analysis. The instrument is capable of monitoring simultaneously many types of gases generated in pyrolysis/combustion. Coupled with a Dupont 951 thermogravimetric analyser (TGA), it has been used for studying the pyrolysis products of polyacrylonitrile (PAN) at different stages of the pyrolysis process. A 1 mg specimen was pyrolyzed in the TGA in a stream of nitrogen or air and the products were introduced to the APCI/MS/MS through a short glass capillary. The molecules of the product were ionized under atmospheric pressure, and analyzed in real time with three serial quadrupole mass filters. The main products were HCN, acetic acid, and a series of nitriles. The generation of each product is discussed in the light of the thermogravimetric analysis.

Aromatic seeding agents for laser ionization in counting gases

Abstract: The yield of ionization of aromates and other substances is investigated by two-photon absorption ionization at 266 nm. Additionally, the UV-extinction coefficients near 266 nm are measured. The yield the ionization is high for substances having high extinction coefficients, and low for furan having a low extinction coefficient. This indicates the dominance of the two-photon resonance ionization process.