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ANALYSIS OF AMBIENT POLAR VOLATILE ORGANIC COMPOUNDS USING CHEMICAL IONIZATION -- ION TRAP DETECTOR
Citation:
Gordon, S. AND M. Miller. ANALYSIS OF AMBIENT POLAR VOLATILE ORGANIC COMPOUNDS USING CHEMICAL IONIZATION -- ION TRAP DETECTOR. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/3-89/070.
Description:
The current approach to measuring trace levels of volatile organic compounds (VOCs) in ambient air requires cryogenic trapping of the analytes, followed by thermal desorption and low-temperature refocussing onto a column for analysis by capillary gas chromatography/mass spectrometry (GC/MS). This approach has been successfully applied to nonpolar VOCs, but its use for more polar species has been complicated by the problems associated with the ambient water vapor collected with the V0Cs. A promising technique for measuring polar VOCs is chemical ionization GC/MS (GC/CI-MS) in the quadrupole ion trap. This approach allows whole air samples to be taken since the water present in the air is used as the CI reagent gas. Water CI leads to appreciable intensities for the proton transfer agent H3O+, which produces intense pseudomolecular ions and class-specific fragmentation patterns for various low molecular weight polar compounds. Standard mixtures of polar species at low concentrations in humidified zero air were analyzed without a membrane dryer, using a cryogenic trap and CI-GC/MS with the ion trap detector in the full scan model. Water appears to be an effective CI reagent gas in the ion trap, and the GC/CI-ITD system can exploit the water vapor normally present in ambient air to circumvent the problems usually encountered in a humid matrix.