Elemental Analysis of Physical Evidence F24

Elemental Analysis of Physical Evidence

Introduction

  • Elemental analysis of various types of forensic evidence provides significant information in forensic chemistry.

  • Enables linking samples to crime scenes or perpetrators.

  • Can identify nutritional deficiencies and their pathophysiological effects.

  • Used to analyze poisons, drugs, medicines, and environmental impacts.

Common Techniques of Elemental Analysis

  • Atomic Spectrometry: Techniques used to measure the absorption and emission of light by atomic species.

    • Atomic Absorption Spectrometry (AAS): Measures light absorbed by vaporized atoms.

    • Atomic Emission Spectrometry (AES): Measures light emitted by atoms when they return to the ground state after excitation.

    • Inductively Coupled Plasma–Mass Spectrometry (ICP-MS): Analyzes elemental composition at molecular levels.

    • X-ray Fluorescence Spectroscopy (XRF): Non-destructive method that analyses elemental composition.

Atomic Spectroscopy

  • Determines both qualitative and quantitative elemental presence, but not functional groups.

  • Sensitive techniques involve flame, furnace, or plasma decomposition.

Atomic Absorption and Emission

  • AAS: Atoms absorb specific light wavelengths, affecting the intensity of the light reaching the detector.

  • AES: Emission from atoms losing energy when thermally excited.

  • Techniques are characterized by the measurement of absorbed or emitted radiation at specific wavelengths.

Applications of AAS in Forensic Science

Glass Analysis

  • AAS and AES techniques are employed to analyze forensic glass samples.

  • AAS offers rapid analysis for single glass elements.

  • ICP–AES facilitates multi-element analysis of glass samples.

  • Key elements to analyze include: Sr, Ti, Fe, Ba, Mn, Ca, Al, Na.

Gun Shot Residue (GSR)

  • AAS effectively used for analyzing GSR primer residues.

  • Sample collection typically involves cotton swabs and dissolution in nitric acid.

  • Concentrations of barium (Ba) and antimony (Sb) are determined in hand swab samples.

  • Aids in linking GSR evidence to sources in firearm cases.

Toxicology

  • AAS and AES are essential for analyzing toxic metals in forensics.

  • Tissue samples require acid digestion; blood and urine may not need this.

  • Hair is commonly studied for toxicological analyses using atomic spectrometry.

Inductively Coupled Plasma Techniques

ICP–AES

  • Utilizes inductively coupled plasma to detect chemical elements through electromagnetic radiation emitted from excited atoms.

  • Analyzes a variety of forensic evidence, including food and trace elements in proteins.

ICP–MS

  • Detects metals and nonmetals at very low concentrations.

  • Facilitates discrimination of glass from different sources.

  • Laser Ablation ICP-MS (LA-ICP-MS): Allows for the analysis of specimens while avoiding complete destruction.

Applications of ICP-MS-LA

  • Paint Analysis: Provides qualitative and semi-quantitative data on paint samples without needing sample preparation.

  • GSR Analysis: Enables detailed examination of lead isotope ratios and trace elements in damaged bullet fragments.

X-Ray Fluorescence Spectroscopy (XRF)

  • Non-destructive method measuring elemental composition through X-ray interactions with atoms.

  • Provides specific elemental data correlated to the energy level of X-ray fluorescence peaks.

  • Portable XRF devices enhance on-scene analysis, yielding immediate results.

  • Effective for analyzing glass, soil, rocks, and determining purity in precious metals.