Development of a stigmatic mass microscope using laser desorption∕ionization and a multi-turn time-of-flight mass...

A novel stigmatic mass microscope using laser desorption∕ionization and a multi-turn time-of-flight mass spectrometer, MULTUM-IMG, has been developed. Stigmatic ion images of crystal violet masked by a fine square mesh grid with a 12.7 μm pitch as well as microdot patterns with a 5 μm dot diameter and a 10 μm pitch made with rhodamine B were clearly observed. The estimated spatial resolution was about 3 μm in the linear mode with a 20-fold ion optical magnification. Separating stigmatic ion images according to the time-of-flight, i.e., the mass-to-charge ratio of the ions was successfully demonstrated by a microdot pattern made with two different dyes, crystal violet and methylene blue. Stigmatic ion images of a microdot pattern made with crystal violet were observed after circulation in MULTUM-IMG, and the pattern of the ion image was maintained after ten cycles in MULTUM-IMG. A section of a mouse brain stained with crystal violet and methylene blue was observed in the linear mode, and the stigmatic total ion image of crystal violet and methylene blue agreed well with the optical microphotograph of the hippocampus for the same section.