  Biological tissue imaging by secondary ion mass spectrometry has seen rapid
development with the commercial availability of polyatomic primary ion sources.
Endogenous lipids and other small bio-molecules can now be routinely mapped on
the sub-micrometer scale. Such experiments are typically performed on
time-of-flight mass spectrometers for high sensitivity and high repetition rate
imaging. However, such mass analyzers lack the mass resolving power to ensure
separation of isobaric ions and the mass accuracy for elemental formula
assignment based on exact mass measurement. We have recently reported a
secondary ion mass spectrometer with the combination of a C60 primary ion gun
with a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS)
for high mass resolving power, high mass measurement accuracy and tandem mass
spectrometry capabilities. In this work, high specificity and high sensitivity
secondary ion FT-ICR MS was applied to chemical imaging of biological tissue.
An entire rat brain tissue was measured with 150 um spatial resolution (75 um
primary ion spot size) with mass resolving power (m/{\Delta}m50%) of 67,500 (at
m/z 750) and root-mean-square measurement accuracy less than two
parts-per-million for intact phospholipids, small molecules and fragments. For
the first time, ultra-high mass resolving power SIMS has been demonstrated,
with m/{\Delta}m50% > 3,000,000. Higher spatial resolution capabilities of the
platform were tested at a spatial resolution of 20 um. The results represent
order of magnitude improvements in mass resolving power and mass measurement
accuracy for SIMS imaging and the promise of the platform for ultra-high mass
resolving power and high spatial resolution imaging.
