Forensic chemical analysis uses a variety of scientific techniques to identify, separate, and measure chemical substances found in crime-related evidence. These techniques help forensic chemists determine what a substance is, how it was used, and where it came from.
Here are some of the most common techniques used:
1. Chromatography
Chromatography separates mixtures into their individual components so they can be identified and measured.
- Gas Chromatography (GC): Used to analyze volatile substances such as drugs, arson residues, and explosives.
- High-Performance Liquid Chromatography (HPLC): Used for non-volatile or heat-sensitive substances like poisons or pharmaceuticals.
- Thin-Layer Chromatography (TLC): A simple method to compare samples, such as inks or dyes.
2. Spectroscopy
Spectroscopy identifies substances by studying how they interact with light or other radiation.
- Infrared (IR) Spectroscopy: Identifies chemical bonds and functional groups in unknown substances like drugs or fibers.
- Ultraviolet-Visible (UV-Vis) Spectroscopy: Measures how substances absorb light; useful in drug and blood analysis.
- Atomic Absorption Spectroscopy (AAS): Detects metals in gunshot residues or poisons.
- Mass Spectrometry (MS): Provides the molecular structure and exact composition of a compound. Often combined with GC or LC (GC-MS or LC-MS) for more precise identification.
3. Microscopy
Microscopy allows chemists to examine tiny samples visually.
- Used for analyzing fibers, hair, glass fragments, paint chips, and soil particles.
- Specialized microscopes (polarized light or comparison microscopes) help compare evidence samples with known references.
4. X-Ray Techniques
- X-Ray Diffraction (XRD): Determines the crystal structure of substances, useful for analyzing minerals or explosives.
- X-Ray Fluorescence (XRF): Detects and measures elements in materials like glass, paint, or metals.
5. Chemical Spot Tests
Quick, simple tests that produce a color change when a specific chemical is present.
- Used for on-site drug testing, explosive detection, or blood identification.
- Example: The Marquis test for heroin or morphine produces a purple color.
6. Electrophoresis
Separates molecules like DNA, proteins, or dyes based on their electric charge and size.
- Commonly used in biological evidence analysis such as blood or saliva stains.
7. Thermal Analysis
Examines how materials change when heated.
- Helps determine the composition of plastics, fibers, and explosives.
8. Elemental Analysis
Used to determine which elements are present in a sample.
- Techniques like Inductively Coupled Plasma (ICP) or Neutron Activation Analysis (NAA) can detect trace elements in gunshot residues, soil, or metals.
9. pH and Solubility Tests
Simple chemical tests to determine the acidity, alkalinity, or solubility of a substance, providing clues to its identity.
Summary
Common forensic chemistry techniques include:
- Chromatography – separates mixtures.
- Spectroscopy – identifies chemical structures.
- Microscopy – examines small samples.
- X-Ray analysis – identifies elemental and structural composition.
- Spot tests and thermal analysis – provide quick chemical checks.