Ultrahigh Sensitivity PTR-MS Instrument with a Well-Defined Ion Chemistry

Proton-transfer-reactionmass spectrometry (PTR-MS) is widely usedfor measuring organic trace gases in air. In traditional PTR-MS, bothnonpolar and polar analytes are ionized with unit efficiency, as predictedfrom ion-molecule collision theories. This well-defined ion chemistryallows for direct quantification of analytes without prior calibrationand therefore is an important characteristic of PTR-MS. In an effortto further increase the sensitivity, recently developed ultrahighsensitivity chemical ionization mass spectrometry (CIMS) analyzershave, however, been reported to have sacrificed unit ionization efficiencyfor selected analytes or classes of analytes. We herein report onthe development of a novel ultrasensitive PTR-MS instrument, the FUSIONPTR-TOF 10k, which exhibits the same universal unit response as conventionalPTR-MS analyzers. The core component of this analyzer is the newlydesigned FUSION ion-molecule reactor, which is a stack of concentricring electrodes generating a static longitudinal electric field superimposedby a focusing transversal radiofrequency (RF) field. The FUSION PTR-TOF10k instrument is equipped with an improved ion source, capable ofswitching between different reagent ions (H3O+, O-2 (+), NO+, NH4 (+)) in less than one second. The improved time-of-flight mass spectrometeranalyzes m/z signals with a massresolution in the 10000-15000 range. FUSION PTR-TOF 10k achievessensitivities up to 80000 cps ppbV(-1) and detectionlimits down to 0.5 pptV for a 1 s measurement time. We show time-seriesof naphthalene and C-13-napthalene as measured in ambientair in Innsbruck for demonstrating the sub-pptV detection capabilityof this novel FUSION PTR-TOF 10k.