Construction of a novel stigmatic MALDI imaging mass spectrometer

A novel design concept and the status of development of a matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometer in the stigmatic mode utilizing a perfect focusing property of a multi-turn time-of-flight (TOF) ion optics is reported. A multi-turn TOF ion optics consisting of four toroidal electric sectors has ideal features for a mass analyzer of stigmatic imaging mass spectrometry. The constructed multi-turn TOF mass analyzer, MULTUM-IMG, demonstrated a strong focusing property allowing MALDI-generated ions to revolve in a closed orbit for hundreds turns. Images of ion ensembles extracted from matrix surfaces patterned by several sizes of thin grid meshes (100–1000 lines/in.) or from arrays of small pigment dots (approximately 30 μm in diameter) fabricated on Si plates were examined by attaching an imaging detector to a MALDI ion source directly, and were found to retain the original spatially distributing patterns of the samples. Images of a patterned ion ensemble after multiple revolutions in MULTUM-IMG were examined, and were found to retain the images at the entrance of the multi-turn TOF section. The possibility of the novel stigmatic MALDI TOF imaging mass spectrometer has been proven by examining the building blocks.