|Perez Jr, Johnny|
|Watson, David - Temple University|
|Levis, Robert - Temple University|
Submitted to: Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2016
Publication Date: 10/26/2016
Citation: Perez Jr, J.J., Watson, D.A., Levis, R.J. 2016. The classification of gunshot residue using laser electrospray mass spectrometry and offline multivariate statistical analysis. Analytical Chemistry. doi: 10.1021/acs.analchem.6b01438.
Interpretive Summary: Currently, the analysis of gunshot residue focuses on either the organic or inorganic constituents that remain following a deflagration event. For the first time, we demonstrate the ability to simultaneously detect both organic/inorganic components directly from an expended casing without any sample preparation and in a single measurement using nonresonant laser vaporization with mass spectral analysis. This new combination of signature ions followed with offline multivariate statistical analysis allows classification of the residue with respect to its manufacturer suggesting potential use as a rapid triage and adjudicative method for law enforcement agencies.
Technical Abstract: Nonresonant laser vaporization combined with high-resolution electrospray time-of-flight mass spectrometry enables analysis of a casing after discharge of a firearm revealing organic signature molecules including methyl centralite (MC), diphenylamine (DPA), N-nitrosodiphenylamine (N-NO-DPA), 4-nitrodiphenylamine (4-NDPA), a DPA adduct, and multiple unidentified features not observed in previous mass spectral measurements. Collision-induced dissociation measurements of unknown GSR signature ions reveals inorganic barium and derivatives BaOH, BaOHCH(3), BaCH(3)COO remaining from the primer. Both hydrophilic and hydrophobic signatures are detected using water–methanol electrospray solution. Offline principal component analysis and discrimination of the laser electrospray mass spectral (LEMS) measurements resulted in perfect classification of the gun shot residue with respect to the manufacturer. Principal component analysis of recycled and reloaded casings resulted in classification of the penultimate manufacturer with an accuracy of 89%.