Environmental Applications of Soft Ionization with GC–TOFMS and GC–QTOFMS

Abstract Soft ionization used with gas chromatography time-of-flight mass spectrometry (GC–TOFMS) allows for the selective ionization of aliphatic hydrocarbons and polycyclic aromatic sulfur heterocycles in certified standard reference oil (NIST SRM2721) and coal tar (NIST SRM1597a). Soft ionization is accomplished by photoionization from vacuum ultraviolet resonance lines produced by Xe, Kr, and Ar microplasmas. Molecular ion fragmentation of an aliphatic hydrocarbon C 24 H 50 in a TOF mass spectrometer and a QTOF mass spectrometer using Ar and Kr are compared. The advantage of using soft ionization, as compared with the more commonly used electron ionization, lies in the enhancement of the relative intensity of molecular ions, which can be controlled by the choice of plasma gas. Furthermore, the enhanced selectivity provided by the ability to select the ionization wavelength is demonstrated through the qualitative analysis of a series of polycyclic aromatic sulfur heterocycles including dibenzothiophene, naphthothiophene, benzonaphthothiophene, and various methylated derivatives of these compounds.