Laser Ablation Coupled to a Flowing Atmospheric Pressure Afterglow for Ambient Mass Spectral Imaging

A plasma-based ambient desorption/ionization mass spectrometry (ADI-MS) source was used to perform molecular mass spectral imaging. A small amount of sample material was ablated by focusing 266 nm laser light onto a spot. The resulting aerosol was transferred by a nitrogen stream to the flowing afterglow of a helium atmospheric pressure glow discharge ionization source; the ionized sample material was analyzed by a Leco Unique time-of-flight mass spectrometer. Two-dimensional mass spectral images were generated by scanning the laser beam across a sample surface. The total analysis time for a 6 mm2 surface, which is limited by the washout of the ablation chamber, was less than 30 min. With this technique, a spatial resolution of ∼20 μm has been achieved. Additionally, the laser ablation configuration was used to obtain depth information of over 2 mm with a resolution of ∼40 μm. The combination of laser ablation with the flowing atmospheric pressure afterglow source was used to analyze several sample surfaces for a wide variety of analytes and with high sensitivity (LOD of 5 fmol for caffeine).