This report presents the methodology and findings of a research project that developed a platform for achieving the efficient and effective determination of the spatial distribution of small molecules that span a range of polarities in a diversity of sample types without requiring a matrix, vacuum, solvent, or complicated sample pre-treatment steps.
Methods for the achievement of small molecule imaging by mass spectrometry have used sample pre-treatment steps such as cryo-sectioning, dehydration, chemical fixation, or the application of a matrix or solvent to obtain interpretable spatial distribution data; however, these steps, along with requirements of the mass analyzer, such as high vacuum, can limit the range of sample types that can by analyzed by this method. The current project developed a laser ablation-direct analysis in real time imaging-mass spectrometry (LADI-MS) approach that coupled a 213 nm Nd:YAG solid state UV laser to a direct analysis in real time (DART) ion course and high-resolution time-of-flight mass spectrometer. Specifically, the project demonstrated the applicability of LADI-MS to a variety of sample types to address issues relevant to plant chemical ecology and forensic science; for example, the demonstration of the compartmentalization of small molecules can inform practice for the improved efficiency of extracting clinically relevant alkaloids from seed tissue or the removal of potentially carcinogenic molecules in coffee beans. In addition, the developed approach enables the analysis of large and irregularly shaped samples, such as wood slices, and can enable the mapping of the locales of biologically active small molecules in endangered trees to enable the forensic identification of their geographic origin or assessment of the climactic and/or environmental conditions to which the tree was exposed over its life. This technique also enables the collection of optical images and chemical information simultaneously. Extensive tables and figures and 264 references