CI-Orbitrap: an instrument to study atmospheric reactive organic species
Résumé
Oxidation of volatile organic compound (VOC) leads to the formation of an extensive variety of oxygenated VOCs (OVOCs), with some of them being capable of forming and growing aerosols. Recently, the identification of the formation of highly oxygenated organic molecules (HOM) using chemical ionization mass spectrometer (CIMS) represents both an atmospheric science and instrumental breakthrough. The CIMS allows the detection of a wide range of OVOCs. It is usually used with medium to high resolution (from 4000 to 14000) time-of-flight (TOF) mass analyzers providing extensive chemical information for the identification of key compounds. However, for complex mixtures, these mass analyzers can display overlapping ion signals therefore increasing measurement uncertainties.
The goal of this work was to overcome this mass resolution limitation by coupling an Orbitrap mass spectrometer (resolution of 140 000 at m/z 200), to a nitrate-ion-based (NO3-) CI source, known to be highly selective and sensitive towards atmospheric reactive species (including HOM). We analyzed the OVOC generated from two well-known systems (alpha-pinene and limonene ozonolysis) and evaluated the impact of various experimental conditions on the MS signal.
The ultra-high resolving power of the CI-Orbitrap allows an unambiguous identification of all ions while the medium to high resolution TOF mass analyzers do not allow this ion separation and provides more uncertain information. The use of the MS² feature provided novel and useful structural information that could help identifying key compounds. In conclusion, this new analytical instrument can give a better understanding of the formation and fate of atmospheric reactive species.