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Volume 12, issue 9
Atmos. Meas. Tech., 12, 4965–4982, 2019
https://doi.org/10.5194/amt-12-4965-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Meas. Tech., 12, 4965–4982, 2019
https://doi.org/10.5194/amt-12-4965-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Sep 2019

Research article | 13 Sep 2019

Addition of fast gas chromatography to selected ion flow tube mass spectrometry for analysis of individual monoterpenes in mixtures

Michal Lacko1,2, Nijing Wang3, Kristýna Sovová1, Pavel Pásztor1, and Patrik Španěl1 Michal Lacko et al.
  • 1J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejškova 2155/3, 182 23 Prague, Czech Republic
  • 2Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague, Czech Republic
  • 3Air Chemistry Department, Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, 55128 Mainz, Germany

Abstract. Soft chemical ionization mass spectrometry (SCI-MS) techniques can be used to accurately quantify volatile organic compounds (VOCs) in air in real time; however, differentiation of isomers still represents a challenge. A suitable pre-separation technique is thus needed, ideally capable of analyses over a few tens of seconds. To this end, a bespoke fast gas chromatography (GC) instrument with an electrically heated 5 m long metallic capillary column was coupled to selected ion flow tube mass spectrometry (SIFT-MS) measurements. To assess the performance of this combination, a case study of monoterpene isomer (C10H16) analyses was carried out. The monoterpenes were quantified by SIFT-MS using H3O+ reagent ions (analyte ions C10H17+, mz 137, and C6H9+, mz 81) and NO+ reagent ions (analyte ions C10H16+, mz 136, and C7H9+, mz 93). The combinations of the fragment ion relative intensities obtained using H3O+ and NO+ were shown to be characteristic of the individual monoterpenes. Two non-polar GC columns (Restek Inc.) were tested: the advantage of MXT-1 was shorter retention, whilst the advantage of MXT-Volatiles was better separation. Thus, it is possible to identify components of a monoterpene mixture in less than 45 s using the MXT-1 column and to separate them in less than 180 s using the MXT-Volatiles column. Quality of the separation and the sensitivity of present technique (limit of detection, LOD,  ∼ 16 ppbv) was found to be inferior compared to commercially available fast GC solutions coupled with proton transfer reaction mass spectrometry (PTR-MS, LOD  ∼ 1 ppbv) due to the limited sample flow through the column. However, using combinations of two reagent ions improved identification of monoterpenes not well resolved by the chromatograms. As an illustrative example, the headspace of needle samples of three conifer species was analysed by both reagent ions and with both columns showing that mainly α-pinene, β-pinene and 3-carene were present. The system can thus be used for direct rapid monitoring of monoterpenes above 20 ppbv, such as applications in laboratory studies of monoterpene standards and leaf headspace analysis. Limitation of the sensitivity due to the total sample flow can be improved using a multi-column pre-separation.

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The soft chemical ionization analytical technique of selected ion flow tube mass spectrometry, SIFT-MS, was enhanced by a fast GC pre-separation unit to identify individual isomers. Experiments were carried out with two GC columns, MXT-1 and MXT-Volatiles, using two reagent ions, H3O+ and NO+, on monoterpene samples (an artificial mixture and coniferous needles). Analyses of product ion ratios allowed for quantification of multiple monoterpenes in partially separated chromatograms.
The soft chemical ionization analytical technique of selected ion flow tube mass spectrometry,...
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