Microscopic Chemical Imaging with Laser Desorption Mass Spectrometry

Mass spectrometric chemical images of surfaces were obtained using a laser desorption/laser postionization time-of-flight mass spectrometer. Using a single laser to both desorb and ionize surface species results in a large variability in the ion signal as the laser is rastered from spot to spot on the surface. The variation is greatly reduced when the detected species are photoionized desorbed neutrals rather than ions produced directly by the desorption laser. A Schwarzschild microscope mounted outside of the vacuum chamber is used to focus the desorption laser on the sample. Ion dispersion and detection are accomplished by a simple time-of-flight mass analyzer. The spatial resolution of the system is on the order of 1 μm. The design and use of the imaging laser microprobe mass spectrometer are presented, along with images of organic and inorganic surfaces.