Ion-molecule reactions of CoAr6+ with di- and trifluorobenzenes probe absolute pressure in FT-ICR MS

A recently introduced pressure calibration scheme with CoAr6+ as pressure probe agent was reinvestigated with di- and trifluorobenzenes using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. For all reactants ligand exchange was observed as primary reaction. As secondary reactions, ligand exchange and radiative association took place. The results show that pressure calibration for sticky substances is difficult in ultra-high vacuum (UHV), and that ion-molecule reactions which proceed with collision rate are ideal in situ pressure probes. A finite-elements simulation of the UHV pressure as a function of time reproduces the experimental findings. The simulation also shows that the actual reactant gas pressure may exhibit significant drift, which is not visible at the pressure gauge.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (74 K)Download as PowerPoint slideResearch highlights▶ Pressure calibration factors for sticky substances can be pressure-dependent. ▶ Ion-molecule reactions at collision rate serve as in situ pressure gauge. ▶ CoAr6+ is suitable calibration reagent for di- and trifluorobenzenes. ▶ Effects become important at pressures below 10−8 mbar.