Mass spectrometry imaging (MSI) has
become a powerful tool in diverse
fields, for example, life science, biomaterials, and catalysis, for
its ability of in situ and real-time visualization
of the location of chemical compounds in samples. Although laser ablation
(LA) achieves high spatial resolution in MSI, the ion yield can be
very low. We therefore combined an LA system with an ambient ion source
for post-ionization and an atmospheric pressure (AP) inlet mass spectrometer
to construct a novel AP-MSI platform. A dielectric barrier discharge
ionization (DBDI) source is operated in the “active sampling
capillary” configuration, can be coupled to any mass spectrometer
with an AP interface, and possesses high ion transmission efficiency.
This study presents some application examples based on LA-DBDI, a
low-cost and flexible strategy for AP-MSI, which does not require
any sample pretreatment, and we show MS imaging of endogenous species
in a traditional Chinese herbal medicine and of a drug molecule in
zebra fish tissue, with a lateral resolution of ≈20 μm.
Atmospheric pressure mass spectrometry imaging (AP-MSI) is a powerful tool in many fields; however, there are still some difficulties to achieve high spatial resolution for AP-MSI, one of them being the need for a small ablation crater. Here, a fiber probe laser ablation (FPLA) system is introduced that uses an etched optical fiber with a sharp tip (o.d. 200 nm) to deliver ablation laser pulses to a sample surface to ablate materials with high spatial resolution. The tip-to-sample distance was adjusted to ∼10 μm using a micro-actuator having a stepping motor with submicron accuracy. The laser-ablated neutrals were postionized using a home-built in-line dielectric barrier discharge source, which can be interfaced to any mass spectrometer with an AP interface. Using MSI on a standard sample with a striped pattern and sections of fingernails treated with the drug methyl green zinc chloride salt, a FPLA-DBDI-MSI spatial resolution of ≈5 μm was demonstrated.
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