Much of our lab’s research utilizes mass spectrometry techniques to solve problems. Mass spectrometry is a powerful technique on its own, providing a high volume of information about a sample in a relatively short amount of time. Mass spectrometry is what allows us to classify the various plants and drugs we are investigating, identify chemical signatures from rotting flesh and the insects that feed on it, profile the headspace of endangered wood species, and much more. However, this only tells us about what is in a particular sample, not where in the sample that information is coming from. For that, we rely on imaging variations of different mass spectrometry techniques. For example, DART (direct analysis in real-time) allows us to detect the presence of mescaline, a powerful psychoactive, in certain species of cactus. However, to know where in the cactus that compound is concentrated, we turn to MALDI, or matrix-assisted laser desorption/ionization. MALDI-MS imaging allows us to obtain chemical information in 2 dimensions. This is extremely useful in many applications, which include touch chemistry analysis of fingerprints, hair analysis, metabolic pathways of seeds and their chemical components, and more.
The use of MALDI for 2D analysis has many benefits as described, however it also has several shortcomings which can limit its use. The application of matrix, for example, can muddy results in the low mass range, and the need for high vacuum conditions means that extremely volatile samples are lost to the vacuum of the instrument. To remedy this, our lab is developing a novel imaging technique which combines laser ablation and direct analysis in real time-high resolution mass spectrometry. This hybrid technique, dubbed Laser Ablation DART Imaging or LADI-MS, allows us to combine the ambient ionization conditions of DART with the 2D-ready acquisition technique of the laser ablation system. As such, we have demonstrated novel use beyond that which is achievable by MALDI, including analysis of non-conductive substrates like paper, whole seeds and bullets, as well as detection of very volatile compounds such as low molecular weight fatty acids in fingerprints.