Gunshot Residues (GSR) Analysis by Using MALDI Imaging
Recently, matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging techniques have been developed for biological sciences to evaluate and understand the distribution of various chemicals on biological surfaces. In particular, this technique provides useful visual information about the locations of specific chemicals on surfaces.
In this work, we explored the use of MALDI-MS imaging for the forensically applicable sample of gunshot residues (GSR). These measurements were done using a spiral-trajectory ion optics time-of-flight mass spectrometer (SpiralTOF-MS) which has a 17m flight path that provides high resolution capabilities, even down into the lower m/z region. Additionally, the m/z axis remains very stable over the long time period required for MALDI-MS imaging.
Sample Preparation and Measurement
The GSR samples were obtained on an electrically conductive adhesive that was adhered to the back of a shooter’s hand while a handgun was discharged. 2, 5-Dihydroxybenzoic acid (DHB) was dissolved in MeOH at a concentration of
30 mg/mL. Two milliliters of this DHB matrix solution was sprayed onto the GSR using an air-brush. Polypropylene glycol (PPG) was used for the external calibration standard. After the samples were dried, they were measured using the JMS-S3000 SpiralTOF MS system.