Mass spectroscopy electron impact ionization

Nitrobenzene in aqueous samples may be analyzed by GC and GC/MS techniques. Wastewaters and solid and hazardous wastes may be analyzed by EPA Methods 609 (GC) or 625 and 8250 or 8270, respectively, using GC/MS (U.S. EPA 1992, 1997). The characteristic ions to identify nitrobenzene by mass spectroscopy (electron-impact ionization) are 77, 123, and 65. The GC techniques involve the use of FID and NPD (in the nitrogen mode) as detectors. The former is less sensitive than the latter. 

Pyrolysis mass spectroscopy was conducted with a Hewlett-Packard model 5985B gas chromatograph/quadrupole mass spectrometer, operated at sslO- Torr and 70eV electron-impact ionization energy. Samples were introduced into the mass spectrometer via a glass lined direct insertion probe (DIP). The samples were decomposed in the DIP to a nominal temperature of 300°C at a heating rate of 30°C/min. 

FTIR Fourier transform infrared spectroscopy (technique useful in identifying and analyzing various unknown compounds, such as environmental pollutants) GC Gas chromatography (most commonly used analytical technique for organics) GC/MS Gas chromatography/mass spectrometry (technique based on chromatographic separation, followed by chemical or electron-impact ionization and identification of the mass spectra of the ionized fragments)... 

Retinol and retinyl esters tend to dehydrate under the conditions of electron-impact ionization mass spectroscopy, so that the most prominent ion is that of anhydroretmol (m/z 268) instead of retinol (m/z 286), with small but detectable amounts of the parent ion (20). Methyl retinoate and the trimethylsilyl derivative of retinol usually give prominent molecular ions by electron-impact ionization. Chemical ionization usually gives an identifiable adduct to the molecular ion, thus providing useful information on molecular weight. 

Mass spectroscopy is a useful technique for the characterization of dendrimers because it can be used to determine relative molar mass. Also, from the fragmentation pattern, the details of the monomer assembly in the branches can be confirmed. A variety of mass spectroscopic techniques have been used for this, including electron impact, fast atom bombardment and matrix-assisted laser desorption ionization (MALDI) mass spectroscopy. 

A detailed description of sources used in atmospheric pressure ionization by electrospray or chemical ionization has been compiled.2 Atmospheric pressure has been used in a wide array of applications with electron impact, chemical ionization, pressure spray ionization (ionization when the electrode is below the threshold for corona discharge), electrospray ionization, and sonic spray ionization.3 Interferences potentially include overlap of ions of about the same mass-charge ratio, mobile-phase components, formation of adducts such as alkali metal ions, and suppression of ionization by substances more easily ionized than the analyte.4 A number of applications of mass spectroscopy are given in subsequent chapters. However, this section will serve as a brief synopsis, focusing on key techniques. 

Capillary Electrophoresis with Flame Photometric Detection Chemical Weapons Convention Extracted Ion Chromatogram Electron Impact Mass Spectrometry Electrospray Ionization Flow Injection Analysis Flame Photometric Detector Gas Chromatography/Fourier Transform Infrared Spectroscopy Gas Chromatography/Mass Spectrometry Gas chromatography International Union for Pure and... 

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