Development of proton-transfer ion trap-mass spectrometry: on-line detection and identification of volatile organic compounds in air |
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Authors: | Email author" target="_blank">C?WarnekeEmail author J?A?de?Gouw E?R?Lovejoy P?C?Murphy W?C?Kuster R?Fall |
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Institution: | 1.Aeronomy Laboratory,National Oceanic and Atmospheric Administration,Boulder,USA;2.Cooperative Institute for Research in Environmental Sciences,University of Colorado,Boulder,USA;3.Department of Chemistry and Biochemistry,University of Colorado,Boulder |
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Abstract: | We present a newly developed instrument that uses proton-transfer ion trap-mass spectrometry (PIT-MS) for on-line trace gas
analysis of volatile organic compounds (VOCs). The instrument is based on the principle of proton-transfer reaction-mass spectrometry
(PTR-MS): VOCs are ionized using PTRs and detected with a mass spectrometer. As opposed to a quadrupole mass filter in a PTR-MS,
the PIT-MS instrument uses an IT-MS, which has the following advantages: (1) the ability to acquire a full mass spectrum in
the same time as one mass with a quadrupole and (2) extended analytical capabilities of identifying VOCs by performing collision-induced
dissociation (CID) and ion molecule reactions in the IT. The instrument described has, at its current status, limits of detection
between 0.05 and 0.5 pbbv for 1-min measurements for all tested VOCs. The PIT-MS was tested in an ambient air measurement
in the urban area of Boulder, Colorado, and intercompared with PTR-MS. For all measured compounds the degree of correlation
between the two measurements was high (r
2 > 0.85), except for acetonitrile (CH3CN), which was close to the limit of detection of the PIT-MS instrument. The two measurements agreed within less than 25%,
which was within the combined measurement uncertainties. Automated CID measurements on m/z 59 during the intercomparison were used to determine the contributions of acetone and propanal to the measured signal; both
are detected at m/z 59 and thus are indistinguishable in PTR-MS. It was determined that m/z 59 was mainly composed of acetone. An influence of propanal was detected only during a high pollution event. The advantages
and future developments of PIT-MS are discussed. |
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