Multi-scheme chemical ionization inlet (MION) for fast switching of reagent ion chemistry in atmospheric pressure chemical ionization mass spectrometry (CIMS) applications
Abstract. A novel chemical ionization inlet named the Multi-scheme chemical IONization inlet (MION), Karsa Ltd., Helsinki,
Finland) capable of fast switching between multiple reagent ion schemes is
presented, and its performance is demonstrated by measuring several known
oxidation products from much-studied cyclohexene and α -pinene
ozonolysis systems by applying consecutive bromide ( Br− ) and nitrate
( NO 3 - ) chemical ionization. Experiments were performed in flow
tube reactors under atmospheric pressure and room temperature (22  ∘ C) utilizing an atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF-MS, Tofwerk Ltd., Thun, Switzerland) as the detector.
The application of complementary ion modes in probing the same steady-state
reaction mixture enabled a far more complete picture of the detailed
autoxidation process; the HO2 radical and the least-oxidized reaction
products were retrieved with Br− ionization, whereas the highest-oxidized reaction products were detected in the NO 3 - mode,
directly providing information on the first steps and on the ultimate endpoint of
oxidation, respectively. While chemical ionization inlets with multiple
reagent ion capabilities have been reported previously, an application in
which the charging of the sample occurs at atmospheric pressure with
practically no sample pretreatment, and with the potential to switch the
reagent ion scheme within a second timescale, has not been introduced
previously. Also, the ability of bromide ionization to detect
highly oxygenated organic molecules (HOM) from atmospheric autoxidation reactions has not been demonstrated
prior to this investigation.