Cholic acid spin-coated with acetone mass spectrum in NP-SIMS in negative mode

Cholic acid is a primary bile acid and is an important biological molecule. Despite its biological importance, it is reported for the first time in nanoprojectile-SIMS (NP-SIMS) and to the best of our knowledge in SIMS in general. The samples were prepared by spin-coating a solution of cholic acid in acetone onto a clean silicon wafer. The spin-coating resulted in a porous surface structure. Mass spectra were acquired by NP-SIMS, which involves bombarding the target with individual nanoparticles resolved in space and time, and ultimately recording the secondary ions from each impact individually. The experiments were run on a custom-built ToF-mass spectrometer equipped with a fullerene effusion source. Fullerene projectiles were accelerated at 25 keV for the mass spectra acquisition. The data presented here encompass the results not specific to NP-SIMS, i.e., the secondary ion distribution, the ion co-emission, and the secondary ion spatial distribution on the detector.