Reliability of Fourier Transform-Ion Cyclotron Resonance Determinations of Rate Constants for Ion/Molecule Reactions

Abstract

The results of gas-phase rate constant measurements by Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry may be influenced by the setting of instrumental parameters. The effects of pressure, ionization duration, ionization energy, selection of the parent ion, mass range, trapping potential, reaction delay and pumping-regulation-valve opening have been investigated and analysed using a two-level Plackett–Burman statistical design which is described in an appendix. This approach was tested on the ion/molecule reaction between acetyl ion and acetone: CH₃CO⁺ + CH₃COCH₃ → CH₂CO + (CH₃COCH₃)H⁺. Although space-charge effects are known to be deleterious to FT-ICR, this is the first study demonstrating, on a statistical basis, the necessity of parent ion selection for obtaining reliable rate constants. Considered independently, the other factors tested do not appear statistically significant, but the possibility of interactions among them is discussed. The mean of the rate constants from experiments with acetyl ion selection, k_abs = (2.14 ± 0.18) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, is compared with literature data.