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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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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
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 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 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.

Citation: Obersteiner, F., Bönisch, H., and Engel, A.: An automated gas chromatography time-of-flight mass spectrometry instrument for the quantitative analysis of halocarbons in air, Atmos. Meas. Tech., 9, 179-194, https://doi.org/10.5194/amt-9-179-2016, 2016.
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Short summary
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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