Portable Raman Spectroscopy in Forensics: Explosive Residues and Inflammable Liquids

Significance of the Topic

Forensic investigations rely on identifying chemical traces at crime scenes to link suspects and events. Portable Raman spectroscopy provides rapid, noninvasive on-site analysis of explosives and flammable liquids, enhancing decision making, evidence preservation, and operational safety in forensic and security contexts.

Objectives and Study Overview

This work evaluates a modern portable Raman spectrometer for two key forensic scenarios: identification of pre- and post-blast explosive residues and detection of flammable liquids inside sealed glass containers. The goals include optimization of acquisition settings, demonstration of spectral discrimination, and validation of field performance under realistic conditions.

Methodology

Acquisition parameters were systematically optimized, resulting in five scans per spectrum, 0.5 second integration time, and 10 percent laser power to balance sensitivity and safety. Two modes of analysis were performed: direct sampling with the Raman probe for bulk materials and microscope coupling for microscopic residue examination. Baseline correction and multivariate analysis were applied to enhance classification.

Instrumentation Used

• i-Raman Pro portable Raman spectrometer with 785 nanometer laser and detector cooled to minus 25 degrees Celsius
• Direct Raman probe for bulk sample interrogation
• Microscope attachment for detection of microscopic particles
• BWSpec software for spectrum collection and export to chemometric platforms

Key Results and Discussion

• Pre- and post-blast explosives: Organic explosives (TNT, TATP, PETN) and inorganic oxidizers (ammonium nitrate, potassium nitrate, sodium chlorate) were successfully identified. High spectral resolution enabled discrimination of ammonium nitrate and potassium nitrate differing by 7 inverse centimeters.
• Principal component analysis separated all studied explosives and salts with over 90 percent confidence, supporting robust field classification.
• Post-blast residues from dynamite, ANFO, and chloratite detonations were detected as microscopic particles and assigned to their primary oxidizer components via microscope-coupled Raman.
• Flammable liquids in glass bottles: Gasoline, diesel, ethanol, and acetone inside sealed containers yielded clear Raman signatures with minimal glass interference. PCA achieved over 95 percent confidence in distinguishing these liquids.

Benefits and Practical Applications

By enabling rapid, noninvasive in-situ analysis, portable Raman spectroscopy supports first responders, forensic experts, and security personnel in:

• On-site screening of explosive devices and incendiary threats without sample destruction
• Enhanced safety through remote detection of hazardous materials
• Reduction of laboratory workload by triaging samples in the field

Future Trends and Applications

Emerging developments are expected to include expanded spectral libraries for novel threats, improved detector cooling and laser power for enhanced sensitivity, machine learning integration for automated identification, and hybrid spectroscopic approaches for comprehensive multianalyte detection. Such advances will broaden the scope of field-forward forensic and security analyses.

Conclusion

The i-Raman Pro portable spectrometer achieves laboratory-grade performance for forensic applications in the field. Its cooled detector and microscope coupling provide high-resolution discrimination of closely related explosives, microscopic residue analysis, and noninvasive detection of flammable liquids, reinforcing its value as a frontline analytical tool.

References

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• F Zapata and C García-Ruiz, Determination of nanogram microparticles from explosives after real open-air explosions by confocal Raman microscopy, Anal Chem, 2016, 88, 6726–6733
• C Martín-Alberca, M López-López and C García-Ruiz, Analysis of pre-ignited Improvised Incendiary Devices using portable Raman, Talanta, 2015, 144, 612–618