by PRIYA DAS, AFRS Volunteer
Introduction :-
Spectroscopy is the
scientific study of the interaction between matter and electromagnetic
radiation. It plays a crucial role in identifying the composition, structure,
and properties of substances by analyzing how they absorb, emit, or scatter
light. In forensic science, spectroscopy is a non-destructive, highly sensitive
technique used to analyze trace evidence, biological samples, and chemical
substances found at crime scenes.
Principle :-
Spectroscopy is based on
the principle that atoms and molecules absorb and emit electromagnetic
radiation at specific wavelengths. These interactions produce unique spectral
patterns—like fingerprints—that can be used to identify substances. The
Beer-Lambert Law governs absorption spectroscopy, stating that absorbance is
directly proportional to the concentration of the absorbing species and the
path length of the sample.
Types of Spectroscopy :-
1. Infrared (IR)
Spectroscopy: Analyzes the absorption of infrared radiation by molecules.
2.
Ultraviolet-Visible (UV-Vis) Spectroscopy: Measures the absorption of
ultraviolet and visible light by molecules.
3. Nuclear Magnetic
Resonance (NMR) Spectroscopy: Analyzes the interaction between nuclear
spins and magnetic fields.
4. Mass Spectrometry
(MS): Measures the mass-to-charge ratio of ions.
Working procedure :-
The working of
spectroscopy involves the following steps:
1. Sample Preparation:
A sample is prepared, which can be a solid, liquid, or gas.
2. Radiation Source:
A radiation source, such as a lamp or laser, is used to irradiate the sample.
3. Interaction with
Matter: The radiation interacts with the sample, causing energy transitions
within the atoms or molecules.
4. Detection: The
radiation that is absorbed, reflected, or emitted by the sample is detected
using a detector.
5. Spectrum Analysis:
The detected radiation is analyzed to produce a spectrum, which is a plot of
the intensity of the radiation against wavelength or frequency.
Forensic Significance:-
1. Biological Evidence
- UV-Vis
Spectroscopy:
Detects blood, semen, and saliva by analyzing absorbance patterns.
- Raman
Spectroscopy:
Differentiates between natural and synthetic fibers.
2. Chemical Evidence
- Mass
Spectrometry (MS):
Identifies drugs, toxins, and explosives.
- Gas
Chromatography-MS (GC-MS): Separates and identifies complex mixtures like
narcotics or accelerants.
3. Trace Evidence
- Infrared
Spectroscopy (IR):
Analyzes paint, glass, and soil samples.
- X-ray
Fluorescence (XRF):
Detects elemental composition of metals and residues.
4. Document Examination
- Raman
and IR Spectroscopy:
Detects ink composition and alterations.
- UV
Spectroscopy:
Reveals hidden writing or forged signatures.
5. Fire and Explosive Analysis
- GC-MS
and IR:
Identify accelerants and explosive residues.
Advance Version :-
Modern advancements have led to
portable and hybrid instruments:
- Hyphenated
Techniques:
GC-MS, LC-MS, LC-NMR combine separation and identification.
- Hyperspectral
Imaging:
Combines imaging and spectroscopy for spatial chemical mapping.
- AI
Integration:
Machine learning algorithms enhance spectral interpretation.
Reference :-
