Secondary-ion mass spectrometry (SIMS) of organic compounds. I. Sample preparation methods

Highly porous targets for SIMS were prepared by thermal decomposition of metal compounds on foils of the respective metals. Compounds and foils of silver, gold and tantalum were compared with respect to secondary-ion (SI) intensities measured after spreading solutions of a test substance, phenylalanine hydrochloride, on the porous metal surface. Highest SI intensities were found with silver surfaces obtained after thermal decomposition of silver carbonate. SI intensities depend on primary-(argon) ion flux, on the concentration of the spread solution, and on additives, such as proton donators. It was found that porous targets perform much better than smooth ones with respect to avoiding rapid depletion of substances from the area of the target hit by the primary ions. Further improvement was achieved in some cases by covering the target with a mixture of the sample and some involatile solvent, such as glycerol.