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

Area of Science:

• Forensic Chemistry
• Analytical Chemistry
• Explosives Analysis

Background:

• Quantifying post-blast explosive residue is uncommon in crime labs due to perceived lack of legal relevance.
• However, residue distribution data can inform future sample collection strategies and analytical method development for improvised explosive devices (IEDs).

Purpose of the Study:

• To develop and validate a quantitative analytical method for residues of double-base smokeless powder (DBSP) on post-blast pipe bomb fragments.
• To investigate the distribution patterns of DBSP residues (nitroglycerin, diphenylamine, ethyl centralite) on fragmented PVC pipe bombs.

Main Methods:

• Total vaporization solid phase microextraction gas chromatography mass spectrometry (TV-SPME/GC/MS) was employed.
• The method was optimized for high throughput (separation < 5 min) and high sensitivity (detection limit < 1 ppb).
• Quantification focused on nitroglycerin (NG) as the most indicative DBSP marker.

Main Results:

• The analytical method successfully quantified NG, diphenylamine (DPA), and ethyl centralite (EC) on post-blast PVC pipe bomb fragments.
• Average NG recovered per device was 1.0 mg, with DPA averaging 24 μg; EC was detected infrequently.
• Typical NG concentration on fragments was 15-30 ppm, with no correlation to fragment mass.
• Residue concentration was highest on end cap fragments, indicating specific distribution patterns.

Conclusions:

• TV-SPME/GC/MS provides a sensitive and rapid method for quantifying DBSP residues in post-blast investigations.
• Residue distribution analysis, particularly the concentration on end caps, offers valuable insights for forensic investigations and method optimization.
• This quantitative approach enhances the potential legal relevance of explosive residue analysis in IED cases.