Analysis of metastable ions in the ToF-SIMS spectra of polymers

This paper describes a simplified method to determine the parent and daughter ions of metastable peaks observed using a single stage reflectron ToF-SIMS instrument. The method requires two or more spectra, acquired with different reflector potentials and relies on the use of the apparent mass of the metastable, rather than the time-of-flight required by previous methods. We demonstrate the origin of metastable peak shapes, which depend upon the mass ratio of daughter and parent ions, the kinetic energy released during the decay process and the kinetics of the decay process. We highlight the difficulty of obtaining information from these shapes. The metastables of four common polymers, poly(ethyleneoxide), poly(lactide), poly(methylmethacrylate) and poly(tetrafluoroethylene) are used to provide comprehensive maps of the important in-flight fragmentation reactions. These maps demonstrate that the polymer structure is generally retained for high mass ions and the origin of the C4H9O2+ secondary ion in poly(lactide), a prominent but puzzling ion, is explained.