Technical NoteMapping smokeless powder residue on PVC pipe bomb fragments using total vaporization solid phase microextraction

- Typical concentrations of nitroglycerin on PVC bomb fragments were 15-30 μg/g.
- The highest concentrations of NG were seen on end cap fragments.
- The end caps provide some shielding, which preserves post-blast residues.
- The total amount of NG recovered from a PVC device was ∼1 mg.

Quantitating post-blast explosive residue is not a common practice in crime labs as it is typically not legally relevant. There is value in quantitation, however, if the distribution of residues on Improvised Explosive Devices (IEDs) can help guide future sample collection and/or method development. Total vaporization solid phase microextraction gas chromatography mass spectrometry (TV-SPME/GC/MS) was used to quantify residues of double-base smokeless powder (DBSP), which includes nitroglycerin (NG), diphenylamine (DPA), and ethyl centralite (EC) on post-blast PVC pipe bomb fragments. The analytical method could separate the three constituents in under 5 min with a detection limit under 1 ppb, which demonstrates high throughput while maintaining high sensitivity. The method was optimized for nitroglycerin, as it is the most indicative of DBSP. The average mass of nitroglycerin recovered from an entire PVC device was 1.0 mg. The average mass of diphenylamine recovered was much lower (24 μg) and only one device had detectable levels of EC. The typical concentration of NG on any given fragment was approximately 15-30 ppm (μg NG/g fragment). However, there was no correlation between the mass of a fragment and the mass of residue upon it. Instead, the residue was distributed such that the highest concentration of residues was found on end cap fragments.