Portable Raman Spectroscopy in Forensics: Explosive Residues and Inflammable Liquids

Importance of the Topic

Forensic chemistry plays a critical role in crime scene investigations by identifying trace evidence of explosives and flammable liquids on-site. Portable Raman spectroscopy enables rapid, non-invasive identification, improving safety and decision-making for first responders and forensic teams.

Objectives and Overview

This study evaluates a portable Raman system for in situ detection of pre- and post-blast explosive residues and sealed flammable liquids. It aims to demonstrate fast, accurate identification of organic explosives, inorganic oxidizers, and common combustibles without sample preparation.

Methodology

• Sampling: Analysis of ~0.2 mg samples of organic explosives (TNT, TATP, PETN) and inorganic salts (ammonium nitrate, potassium nitrate, sodium chlorate), plus post-blast residues from dynamite, ANFO and chloratite explosions.
• Instrument settings: 785 nm laser, 5 scans, 0.5 s acquisition time, 10% laser power optimized to prevent sample degradation.
• Data processing: Baseline correction, spectral comparison with libraries and chemometric evaluation using principal component analysis (PCA).

Used Instrumentation

• i-Raman Pro portable Raman spectrometer (B&W Tek) with 785 nm laser and -25 °C cooled detector for enhanced resolution and signal-to-noise ratio.
• Direct probe analysis and portable microscope attachment for examining microscopic particles.
• BWSpec software for spectrum acquisition, with export to advanced chemometric tools.

Main Results and Discussion

• Pre-blast analysis yielded high-quality Raman spectra for organic explosives and inorganic salts, enabling clear discrimination of closely related compounds such as ammonium vs. potassium nitrate.
• PCA demonstrated statistical separation of all studied explosives (91% confidence) and flammable liquids (96% confidence).
• Post-blast residues were successfully detected and identified via the portable microscope, revealing ammonium nitrate and sodium chlorate particles from explosive debris.
• Non-invasive probe measurements through glass bottles provided accurate Raman signatures of gasoline, diesel, ethanol and acetone with minimal glass interference.

Practical Benefits and Applications

• Rapid on-site explosive identification accelerates forensic workflows and supports real-time decisions.
• Non-destructive analysis of sealed incendiary devices enhances operator safety and evidence integrity.
• Microscopic analysis capability extends detection to trace residues without sample handling.

Future Trends and Opportunities

Continued improvements in portable spectrometer sensitivity and expanded spectral libraries will broaden detectable substances. Integration of real-time chemometric algorithms can automate field identification. Future handheld systems may combine Raman with complementary techniques (e.g., FTIR) to enhance analytical confidence and versatility in forensic, security and counterterrorism applications.

Conclusion

The portable i-Raman Pro system demonstrated reliable in-situ identification of explosives and flammable liquids under realistic forensic conditions. Its cooled detector and versatile probe options deliver high-resolution spectra for discriminating similar compounds and analyzing minute residues. Adoption of portable Raman enhances forensic efficiency, reduces analysis time and improves safety in hazardous investigations.

References

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6. F. Zapata, C. García‐Ruiz, Determination of nanogram microparticles from explosives after real open‐air explosions by confocal Raman microscopy, Anal. Chem. 2016, 88, 6726‐6733.
7. C. Martín‐Alberca et al., Analysis of pre‐ignited Improvised Incendiary Devices using portable Raman, Talanta 2015, 144, 612‐618.