DETECTION OF CF3-CONTAINING COMPOUNDS IN BACKGROUND AIR BY GAS-CHROMATOGRAPHY HIGH-RESOLUTION MASS-SPECTROMETRY

The application of a dual-sector high-resolution mass spectrometer (HR MS) to the detection of several CF3-containing compounds in Earth's at mosphere is described. By this technique, the contents of air samples collected in remote areas surrounding Bozeman, Montana, are introduced to the HRMS by gas chromatography (GC) while the HRMS is tuned to the exact masses of the ions expected in the electron impact ionization o f each compound. By the analysis procedure developed here, the mass sc ale of the instrument is continuously recalibrated during the analysis so that any level of mass resolution that is required for the complet e separation of hydrocarbon-based from halocarbon-based ions of the sa me nominal mass can be selected. Owing to the unusually large ion opti c system of the mass spectrometer, high ion throughput to the detector is maintained even when higher levels of mass resolution are selected . By this technique, the sensitive detection of CF4 (CFC-14), CF3Cl (C FC-13), CHF3 (HFC-23), CF3CF2Cl (CFC-115), CF3Br (halon-1301), and CF3 CH2F (HFC-134a) in background air samples is demonstrated using essent ially all of the major ions that appear in the electron impact mass sp ectrum of each compound. Most of these compounds are thought to be pre sent in background air at the low parts-per-trillion by volume level. This is one of only two reports, to date, of CHF3 presence in backgrou nd air. A potential source of this compound is suggested by additional measurements provided here.