An automated gas chromatography time-of-flight mass spectrometry instrument for the quantitative analysis of halocarbons in air

Abstract

Abstract. We present the characterization and application of a new gas chromatography time-of-flight mass spectrometry instrument (GC-TOFMS) for the quantitative analysis of halocarbons in air samples. The setup comprises three fundamental enhancements compared to our earlier work (Hoker et al., 2015): (1) full automation, (2) a mass resolving power R = m/ m of the TOFMS (Tofwerk AG, Switzerland) increased up to 4000 and (3) a fully accessible data format of the mass spectrometric data. Automation in combination with the accessible data allowed an indepth characterization of the instrument. Mass accuracy was found to be approximately 5 ppm in mean after automatic recalibration of the mass axis in each measurement. A TOFMS configuration giving R = 3500 was chosen to provide an R-to-sensitivity ratio suitable for our purpose. Calculated detection limits are as low as a few femtograms by means of the accurate mass information. The precision for substance quantification was 0.15 % at the best for an individual measurement and in general mainly determined by the signal-to-noise ratio of the chromatographic peak. Detector non-linearity was found to be insignificant up to a mixing ratio of roughly 150 ppt at 0.5 L sampled volume. At higher concentrations, non-linearities of a few percent were observed (precision level: 0.2 %) but could be attributed to a potential source within the detection system. A straightforward correction for those non-linearities was applied in data processing, again by exploiting the accurate mass information. Based on the overall characterization results, the GC-TOFMS instrument was found to be very well suited for the task of quantitative halocarbon trace gas observation and a big step forward compared to scanning, quadrupole MS with low mass resolving power and a TOFMS technique reported to be non-linear and restricted by a small dynamical range.

Airborne limb-imaging measurements of temperature, HNO<sub>3</sub>, O<sub>3</sub>, ClONO<sub>2</sub>, H<sub>2</sub>O and CFC-12 during the Arctic winter 2015/2016: characterization, in situ validation and comparison to Aura/MLS

“…As was initially shown by infrared limb-emission observations (Clarmann et al, 1993;Oelhaf et al, 1994;Roche et al, 1994), chlorine deactivation in the Arctic spring region results in strong enhancement of ClONO 2 . The retrieved ClONO 2 distribution in Fig.…”

“…Additionally the Gas Chromatograph for the Observation of Stratospheric Tracers-Mass Spectrometer (GhOST-MS) provides measurements of CFC-12 in the electron capture detector channel (Obersteiner et al, 2016).…”

History of chemically and radiatively important atmospheric gases from the Advanced Global Atmospheric Gases Experiment (AGAGE)

“…At the Empa and SIO laboratories, efforts are also underway to upgrade current Medusa technology to time-offlight mass spectrometry (TOF-MS) in place of quadrupole mass spectrometric detection. This offers the advantage of very high mass resolution (∼ 4000) that is capable of separating gases with the same integer masses but different actual masses that interfere with each other in the chromatograms using quadrupole technology (e.g., Obersteiner et al, 2016).…”

An aircraft gas chromatograph–mass spectrometer System for Organic Fast Identification Analysis (SOFIA): design, performance and a case study of Asian monsoon pollution outflow

“…The disadvantage of this method is the reduced cooling capacity with associated limitations in retaining high-vapour-pressure substances. A further solution has been the use of Stirling coolers, as demonstrated by Obersteiner et al (2016b) and Lerner et al (2017). These only require electrical power and hence are eminently suitable for long-term use at remote locations.…”

“…Importantly, when targeting fast measurement times, the MS allows the separation of co-eluting substances that can be distinguished by their different mass and fragmentation patterns. While considerable improvements on the mass resolving power and speed could be achieved with a time-offlight mass spectrometer (TOF-MS) that can simultaneously measure all mass-to-charge signals at high frequency, detector non-linearities of the instrument sensitivity have been observed (Hoker et al, 2015;Obersteiner et al, 2016a). Generally, for all systems, prior to detection, the substances of interest are pre-concentrated in an enrichment trap, where low temperatures are used to retain them.…”