Instrument design and characterization for high resolution MALDI‐MS imaging of tissue sections

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Abstract
In previous work, we have reported using a MALDI imaging time-of-flight mass spectrometer for the detection of protein ions from tissue sections with spatial resolution of 25 µm. We present here imaging mass spectrometry results obtained with a high-resolution scanning MALDI time-of-flight mass spectrometer, equipped with a coaxial laser illumination ion source, capable of achieving irradiation areas as small as 40 µm2 (ca 7 µm diameter). MALDI-generated analyte ion signals from these very small irradiation volumes can be observed in a molecular weight range up to 27 000. High-resolution imaging mass spectrometry images were successfully generated from matrix thin film samples and tissue sections with scanning resolutions at and below 10 µm. This work also provides fundamental characterization of the ion signal dependence as a function of various focus and fluence parameters that will be required for extension to tissue imaging at the subcellular level. Copyright © 2007 John Wiley & Sons, Ltd.