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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 1 | Copyright
Atmos. Meas. Tech., 9, 179-194, 2016
https://doi.org/10.5194/amt-9-179-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 25 Jan 2016

Research article | 25 Jan 2016

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

F. Obersteiner, H. Bönisch, and A. Engel F. Obersteiner et al.
  • Institute for Atmospheric and Environmental Science, Goethe University Frankfurt, Frankfurt, Germany

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 = mm 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 in-depth characterization of the instrument. Mass accuracy was found to be approximately 5ppm 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 150ppt at 0.5L 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.

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We present the characterization and application of a new gas chromatography time-of-flight mass spectrometry instrument, with focus on quantitative analysis of halocarbons in air samples. The applicability of the TOFMS technique, e.g. to form the basis of a "digital air archieve", is supported by the findings of this work: very high sensitivity, high measurement precision, a large dynamical range and an open data format which allows in-depth analysis of the data.
We present the characterization and application of a new gas chromatography time-of-flight mass...
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