Development and Application of Small-molecule Spatial Distribution Imaging: Laser Ablation Direct Analysis in Real Time Imaging-Mass Spectrometry (LADI-MS)

It is often the case that evidence collected at a crime scene must be subjected to multiple analysis methods in order for the full picture of what the evidence shows to emerge.

In an ideal situation, there would be unlimited amounts of a given piece of evidence, and this would allow the performance of all possible types of analyses, the results of which would provide a detailed composite of aspects of the crime and its circumstances.

However, it is usually the case that the amount of a given form of evidence is very limited. In such instances, not all testing methods that are desired can be performed, and difficult decisions must be made about the forms of analysis to which the sample should be subjected in order to acquire data that are most definitive. This common occurrence fuels the continued development of technologies that can provide multiple forms of definitive information within a single experiment. Such methodologies would also streamline the analysis process and reduce the number of forms of analysis that must be performed on a single sample. This in turn would reduce the amount of evidence required for analysis.

The work proposed here would develop such a technique. The system would be capable of rapidly providing small-molecule spatial distribution maps of analyzed forensic evidence with minimal to no sample pre-treatment steps. For example, it would permit the mapping of components such as illicit drugs, “legal” mind-altering plant materials, or explosive materials in an individual’s fingerprints, while maintaining the image of the print. Since the observed print contains both the image of the chemical material to which the criminal has been exposed, and the image of the compounds normally detected by conventional fingerprint development methods, it would provide a direct connection between an individual and other material related to the crime.

The technique proposed in this project would detect alterations made to questioned documents by mapping the spatial distributions of molecules unique to different pen inks (for example). Furthermore, it would enable detection of both inorganics and organics in gunshot residues through performance of a single experiment.

The approach involves the integration of a direct analysis in real time (DART) ion source, a high-resolution time-of-flight mass spectrometer, and a laser ablation system which would be operated in open air and optimized for the rapid, routine and facile detection of the spatial distributions of small-molecules in a wide variety of forensic samples.

ca/ncf