Performance Evaluation of an EI&CI Dual Ionization TOFMS Hyphenated with a Flow Modulated GC×GC System.

ABSTRACT

The use and compatibility of a dual-ionization TOFMS operating an EI source and a CI source in parallel using a single TOF mass analyzer with flow modulated two-dimensional GC (GC×GC) is described. Important figures of merit of the mass spectrometer that are required for two-dimensional GC hyphenation such as acquisition speed, ion source response, EI/CI switching, the GC transfer, and data alignment are carefully investigated and addressed. Improved fast switching ion optics allow switching in a 100 Hz frequency between EI and CI spectra sampled from the same GC×GC effluent. The spectra quality also influenced by the preseparation, especially of the EI source, is compared to a standard setup operating a single quadrupole MS coupled to the same GC system. Further, two setups including and excluding an additional flame ionization detector are presented. High increments in CI sensitivities are achieved by utilizing the high pumping efficiencies of the CI stage of the used mass spectrometer. By leading high flow ratios of the GC×GC modulation flows toward the CI source, the intensity can be increased by factors of up to 37 while maintaining the pressure balance of the less robust EI source. Finally, thermal desorption GC×GC-EI&CI-TOFMS analyses of traffic emission samples from a federal highway in Germany are executed with the presented setup.