English

In this work a novel plasma based chemical ionization (CI) source and its hyphenation with gas chromatography (GC) using a time-of-flight mass spectrometer (TOF MS) is developed. Classical electron beam driven chemical ionization sources often suffer from reduced filament lifetimes and thus require high maintenance efforts. Problems occur especially when using reactive and/or oxidizing reagent gases as well as due to reagent gas degradation product accumulation inside the ion source assembly. The alternative CI method developed in this work is based on the application of H₃+ as primary charge-carrying species and its subsequent conversion via selective reaction cascades using reagent gases which then lead to ionization of the compound of interest. The H₃+ ion is produced with high efficiency in a hydrogen plasma driven with a helical resonator. Since the proton affinity of H₂ is much lower than that of almost all atoms and molecules, H₃+ acts as a universal proton donor via a proton transfer reactions. The respective reagent ion formation of the three reagent gases nitrogen, methane, and isobutane were studied. In contrast to classical CI source operation, the formation of reagent ions and thus analyte ionization occurred mainly via proton transfer reactions. The quantitative transformation of H₃+ into various reagent ion species allows to adjust the exothermicity of the analyte protonation reaction, minimizing the extent of fragmentation. The selectivity and sensitivity of the developed CI method is evaluated for various compounds. The ion source development process is discussed in detail. Four iteratively developed ion source designs were investigated. The performance of each ion source setup is carefully assessed. The final chemical ionization source design exhibits low picogram- to upper femtogram-on-column sensitivity and chromatographic peaks of Gaussian shape with full width at half maximum (FWHM) of < 1 s even for high boiling compounds of a fatty acid methyl ester (FAME) mixture. The customized helical resonator plasma source provides excellent long-term stability and requires low maintenance, while consisting of simple and low-cost hardware.