PTR-MS as a CIMS? Increasing the Range of Detectable Compounds via Low Pressure Negative Soft Chemical Ionization
TOBIAS REINECKE, Markus Leiminger, Markus Mueller,
IONICON Analytik GmbH., Innsbruck, Austria Abstract Number: 198
Working Group: Instrumentation and Methods
AbstractProton-Transfer-Reaction Mass Spectrometry (PTR-MS) is a soft chemical ionization technique to quantitatively detect volatile and condensed organic compounds on a chemical composition level. We recently introduced a next generation PTR-MS, the so-called FUSION PTR-TOF 10k, which merges the advantages of a pristine and well-studied ion-chemistry of a traditional PTR-MS with the high sensitivities and low limits of detection (LOD) of a near-atmospheric pressure chemical ionization mass spectrometer (CIMS). With LODs well below the pptV range, a significantly improved decoupling of the ion-source with the FUSION reaction chamber reducing ionic and neutral interferences and a high resolution TOF-MS (up to 15,000 m/Δm), FUSION PTR-TOF 10k is predestined to study complex mixtures of SOA and respective gas-phase precursors. However, positive chemical ionization with H
3O
+, NH
4+, NO
+, and O
2+ mostly limits the application of PTR-MS to organic compounds (with some exceptions like HNO
3 or NH
3).
For this work, the instrument was equipped with bipolar electronics, capable of switching polarity within seconds. A complete redesign of the FUSION ion-molecule reactor allows operation in a reduced pressure CIMS-like tradition: no drift voltage is applied, ions are solely controlled by RF voltages applied to a series of ring-electrodes. Together with the novel Fast-SRI ion source, negative primary reagent ions like CO
3- and I
- are now additionally accessible, without the need for any hardware modifications. This increases the range of detectable compounds to inorganics like SO
2, H
2SO
4, with 1-min LODs in the single digit pptv range but also other small acids and halogenated compounds become detectable. Additionally, the new FUSION reactor now allows for coupling the instruments with IONICONs renowned particle inlet CHARON. We will present results from a thorough characterization of these new ionization modes based on standards, oxidative flow-tube experiments and ambient measurements for both particle and gas phase.