Simultaneous determination of analyte concentrations, gas-phase basicities, and proton transfer kinetics using gas chromatography/Fourier transform ion cyclotron resonance mass spectrometry (GC/FT-ICR MS)

Details on using analyte gas-phase basicity (GB) or proton affinity (PA) as an additional analysis dimension in GC/FT-ICR MS are reported. Ion–molecule reactions of chemical ionization (CI) reagent ions with the GC separated C1, C2, and C3 aromatic neutral (viz., toluene, m-xylene, and mesitylene) and ketone (acetone, 3-pentanone, and 4-heptanone) molecules were monitored. A suite of CI reagent ions was generated by self-chemical ionization (SCI) of ethanol in an ICR cell. Multiplexed reactant ion monitoring (MRIM) of the CI reagent ions (RiH+) was used for GB bracketing of the neutral analytes eluting from the GC column. The PAs of the conjugate bases (Ri) of the reagent/reactant ions spanned a wide range (∼170 to ∼200 kcal mol−1). A kinetic model was constructed to relate the degree of reactant ion depletion to analyte concentration and proton transfer reaction efficiency. Our experimental GB estimations, based on the thermokinetic data, were in broad agreement with the GB values reported in the NIST database and primary sources (experimental and ab initio). Experimentally measured MRIM chromatogram profiles and kinetic analysis were used to estimate analyte gas-phase pressures in the ICR cell and losses to the surfaces in the ICR vacuum chamber. The MRIM approach permits GB determinations of multiple analytes in a single GC run and provides an additional dimension to improve analytical resolution in GC/FT-ICR MS.