Gathering Evidence by IR and Raman Spectroscopy

Importance of the Topic

Infrared and Raman spectroscopy are essential tools in forensic science, offering rapid and non-destructive identification of illicit and trace materials. Their molecular fingerprinting capabilities enable accurate determination of chemical composition across a wide range of sample types from bulk drugs to microscopic paint flakes.

Study Objectives and Overview

This document surveys the application of FT-IR and Raman spectroscopy in forensic investigations. It focuses on methodologies for identifying drugs, explosives, fibers, particles, paints, and counterfeit items, highlighting both macroscopic screening and microspectroscopic imaging.

Methodology and Instrumentation

• FT-IR Spectroscopy with ATR sampling for fast compound identification and mixture analysis.
• Raman Spectroscopy for non-invasive measurements, depth profiling, and high specificity for pigments and concealed substances.
• Microspectroscopy techniques combining FT-IR and Raman microscopy to analyze samples down to the micrometer scale and generate two-dimensional chemical images.

Instrumentation Used

• ALPHA-P FT-IR spectrometer: portable, battery-powered device for rapid screening of drugs and explosives on-site.
• LUMOS FT-IR microscope: integrated ATR, transmission, and reflection modes with motorized ATR crystal for automated microsample analysis.
• HYPERION 3000 FT-IR microscope: focal plane array imaging for high-resolution chemical mapping of multilayer samples.
• SENTERRA Raman microscope: compact, high-sensitivity system with continuous calibration for pigment and ink analysis.

Key Results and Discussion

• Identification of common and emerging drugs, including cocaine base “crack” adulterated with benzocaine and phenacetin, using mixture analysis in under one minute.
• Detection of plastic explosives (86% PETN) and precursors with FT-IR spectral matching against comprehensive libraries.
• Microscale mapping of fiber samples (~25 µm diameter) and multilayer paint chips, distinguishing individual polymeric layers and producing visual chemical images.
• Automated FT-IR mapping of altered document inks, revealing sequential pen strokes and fraudulent modifications.
• Non-contact Raman identification of historical pigments (e.g., malachite, auripigment) in art authentication studies.

Benefits and Practical Applications

• Rapid analysis under one minute with minimal sample preparation and no consumables.
• Portability and rugged design for in-field and mobile laboratory deployment.
• Extensive spectral libraries (over 26,000 entries) and dedicated new psychoactive substances databases for reliable identification.
• User-friendly software workflows enabling operation by non-specialists.
• High-resolution chemical imaging for detailed trace evidence characterization.

Future Trends and Potential Applications

• AI-driven spectral interpretation to speed up and automate substance identification.
• Expansion of libraries to include novel designer drugs and emerging forensic targets.
• Development of more compact and handheld spectrometers for broader law enforcement use.
• Advances in detector and computation technologies for faster chemical imaging and higher spatial resolution.

Conclusion

The synergy of FT-IR and Raman microspectroscopic techniques provides a robust analytical platform for forensic science. By combining high-speed screening, detailed chemical imaging, and portable instrumentation, these methods enhance reliability, reduce analysis time, and support comprehensive investigations across laboratory and field environments.