Ion-to-neutral conversion in time-of-flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to explore ion-to-neutral conversion on a microsecond time scale. A membrane lipid served as a sample. Neutrals generated from positive ions exhibited rather broad lines in the TOF spectrum, indicating significant transfer of kinetic energy during fragmentation. By contrast, the mass lines of neutrals originating from negative ions with masses up to about m/z 90 were as sharp as the lines of the corresponding ions. At higher masses the lines of “negative neutrals” were usually as broad as those of “positive neutrals”. The neutrals exhibiting sharp lines are assumed to be formed by electron detachment; either spontaneous or electric-field induced. The measured neutral-to-ion yield ratios ranged from 10−3 to 0.2.