Organic Surface Analysis by Two-Laser Ion Trap Mass Spectrometry

This paper describes two-laser ion trap mass spectrometry (L2ITMS) for the analysis of organic, polymeric, and biological surfaces. L2ITMS uses one laser to desorb intact molecules from a surface, a second laser for photoionization, and an ion trap for single or tandem mass spectrometric analysis. We demonstrate the capabilities of this instrument by performing laser desorption/photoionization/tandem mass spectrometric analyses of amino acid and mixed polymer thin films. We then use L2ITMS in conjunction with X-ray photoelectron spectroscopy to chemically analyze the surface of an ion-bombarded polystyrene thin film. Low-energy SF 5 + ion bombardment causes fluorination of intact polystyrene, partial destruction of the aromaticity of the polystyrene, fluorination of the resultant nonaromatic organic material, and sputtering of the polystyrene. The first of these dominates at 50 eV ion energy, while the latter three dominate at 250 eV.