Parallel Operation of Electron Ionization and Chemical Ionization for GC-MS Using a Single TOF Mass Analyzer

This work describes a novel mass spectrometer coupled to gas chromatography (GC-MS) that simultaneously displays the mass spectral information of electron (EI)- and chemical ionization (CI)-generated ion populations for a single chromatographic peak. After GC separation, the eluent is equally split and supplied in parallel to an EI and a novel CI source, both operating continuously. Precise switching of the ion optics provides the exact timing to consecutively extract the respective ion population from both sources and transfer them into a time-of-flight (TOF) mass analyzer. This technique enables the acquisition of complementary information from both ion populations (EI and CI) within a single chromatographic run and with sufficient data points to retain the chromatographic fidelity. The carefully designed GC transfer setup, fast ion optical switching, and synchronized TOF data acquisition system provide an automatic and straightforward spectral alignment of two ion populations. With an eluent split ratio of about 50% between the two ion sources, instrument detection limits of <40 fg on the column (octafluoronaphthalene) for the EI and <2 pg (benzophenone) for the CI source were obtained. The system performance and the additional analytical value for compound identification are demonstrated by means of different common GC standard mixtures and a commercial perfume sample of unknown composition.