Ambient Pressure Laser Desorption Ionization/Postphotoionization Mass Spectrometry Imaging.

Postphotoionization has been demonstrated to be an effective method to increase the ionization efficiency of laser desorption ionization. In order to scan samples with compact and hard characteristics from the front side, an ambient pressure laser desorption ionization in combination with a compact postphotoionization assembly (AP-LDI/PI) in reflection mode was developed. The effects of parameters, including laser energy, frequency, and stepper motor velocity, were carefully investigated. The slices of mouse cerebellum were scanned by AP-LDI/PI mass spectrometry in both positive and negative ion modes with a spatial resolution of 10 μm. In addition, the longitudinal sections of Ginkgo biloba were well imaged using AP-LDI/PI with a spatial resolution of 15 μm. The spatial distributions of metabolites, including ginkgo acids, choline, glutamate, and ethoxycoumarin, within the longitudinal sections of Ginkgo biloba were distinctly delineated.