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Imaging the spatial distribution of molecules in tissue using MALDI mass spectrometers is a rapidly developing technique. The acquisition of accurate mass data in this type of experiment can be hampered in axial MALDI Tof systems. Even small changes in sample position and laser energy in the source region of this type of mass spectrometer affect mass measurement accuracy and mass spectral resolution. Here, we show how the use of an orthogonal Tof MALDI mass spectrometer circumvents these problems by decoupling the MALDI source from the mass analyser.
Imaging data were acquired on a MALDI Q-Tof mass spectrometer. The tissue sections were mounted on a target plate and moved in a raster pattern relative to the laser. To reduce interference from the biological matrix and enhance specificity the instrument was operated in MS/MS mode, a quadrupole was used for precise precursor ion selection. The sensitivity of specific ions was further enhanced by synchronising the high voltage push of the Tof mass analyser with the arrival of ions of appropriate m/z in the acceleration region.
MALDI imaging information has been obtained from thin sections of rat tissue from animals doped with drugs, e.g., the well studied D2/D3 dopamine receptor antagonist Raclopride as well as from untreated animals. Data obtained on the spatial distribution of drugs/drug metabolites and endogenous species will be presented. Challenges and future directions with MALDI imaging sample preparation are discussed.