title: An Ultra-Trace Analysis Technique for SF6 Using Gas Chromatography with Negative Ion Chemical Ionization Mass Spectrometry.
abstract: Sulfur hexafluoride (SF6) is widely used as a tracer gas because of its detectability at low concentrations. This attribute of SF6 allows the quantification of both small-scale flows, such as leakage, and large-scale flows, such as atmospheric currents. SF6's high detection sensitivity also facilitates greater usage efficiency and lower operating cost for tracer deployments by reducing quantity requirements. The detectability of SF6 is produced by its high molecular electronegativity. This property provides a high potential for negative ion formation through electron capture thus naturally translating to selective detection using negative ion chemical ionization mass spectrometry (NCI-MS). This paper investigates the potential of using gas chromatography (GC) with NCI-MS for the detection of SF6. The experimental parameters for an ultra-trace SF6 detection method utilizing minimal customizations of the analytical instrument are detailed. A method for the detection of parts per trillion (ppt) level concentrations of SF6 for the purpose of underground ventilation tracer gas analysis was successfully developed in this study. The method utilized a Shimadzu gas chromatography with negative ion chemical ionization mass spectrometry system equipped with an Agilent J&W HP-porous layer open tubular column coated with an alumina oxide (Al2O3) S column. The method detection limit (MDL) analysis as defined by the Environmental Protection Agency of the tracer data showed the method MDL to be 5.2 ppt.
authors.affiliation: Department of Mining and Minerals Engineering, Virginia Tech, Holden Hall, 445 Old Turner ST, Blacksburg, VA 24061, USA ejong@vt.edu.
authors.forename: Edmund C
authors.initials: EC
authors.lastname: Jong
authors.affiliation: Shimadzu Scientific Instruments, Inc., 7102 Riverwood DR, Columbia, MD 21046, USA.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Macek
authors.affiliation: CDC-Office of Mine Safety and Health Research (OMSHR), P.O. Box 18070, 626 Cochrans Mill RD, Pittsburgh, PA 15236, USA.
authors.forename: Inoka E
authors.initials: IE
authors.lastname: Perera
authors.affiliation: Department of Mining and Minerals Engineering, Virginia Tech, Holden Hall, 445 Old Turner ST, Blacksburg, VA 24061, USA.
authors.forename: Kray D
authors.initials: KD
authors.lastname: Luxbacher
authors.affiliation: Department of Chemistry, Virginia Tech, Hahn Hall, 900 West Campus DR, Blacksburg, VA 24061, USA.
authors.forename: Harold M
authors.initials: HM
authors.lastname: McNair
mesh_terms: D004784:Environmental Monitoring; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D057230:Limit of Detection; D016014:Linear Models; D015203:Reproducibility of Results; D013459:Sulfur Hexafluoride / Q000032:analysis* / Q000737:chemistry*
chemical_list: D013459:Sulfur Hexafluoride