Detection of CF₃‐containing compounds in background air by gas chromatography/high‐resolution mass spectrometry

Abstract

Abstract. The application of a dual-sector high-resolution mass spectrometer (HRMS) to the detection of several CF3-containing compounds in Earth's atmosphere 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 of each compound. By the analysis procedure developed here, the mass scale of the instrument is continuously recalibrated during the analysis so that any level of mass resolution that is required for the complete separation of hydrocarbon-based from halocarbon-based ions of the same nominal mass can be selected. Owing to the unusually large ion optic 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 CF 4 (CFC-14), CF3C1 (CFC-13), CHF 3 (HFC-23), CF3CF2C1 (CFC-115), CF3Br (halon-1301), and CF 3CH2F (HFC-134a) in background air samples is demonstrated using essentially all of the major ions that appear in the electron impact mass spectrum of each compound. Most of these compounds are thought to be present in background air at the low parts-per-trillion by volume level. This is one of only two reports, to date, of CHF 3 presence in background air. A potential source of this compound is suggested by additional measurements provided here.

Feasibility of reconstructing paleoatmospheric records of selected alkanes, methyl halides, and sulfur gases from Greenland ice cores

“…The mass spectrometer is operated in selected ion mode at a mass resolution of 6000 (M/ΔM at 5%), using ion fragments of deuterium (D‐) labeled dodecane as the lock masses. At this mass resolution, halocarbons are fully resolved from hydrocarbons at the same mass to charge ratio [ Engen et al , 1998, 1999]. D‐labeled dodecane is used because its ion fragments do not interfere with fragments from undeuterated atmospheric hydrocarbons, from 13 C‐labeled hydrocarbons used as internal standards, or from halocarbons.…”

Atmospheric Chemistry of Alternative Fuels and Alternative Chlorofluorocarbons

“…In the mid 1990s, the mixing ratio was determined to be 2.0-2.6 pptv. A year later, Engen et al 133 measured a concentration of 4.1 ( 0.8 pptv. Shirai et al 134 report that the concentration is increasing by 83 ( 6% per year and, in 1998, was at 5.9 ( 1.2 pptv.…”