Forensic Hair Sample Analysis using NAA and AAS

Both neutron activation analysis (NAA) and atomic absorption spectroscopy (AAS) are used to estimate the concentration of arsenic in biological samples such as hair, nails, and bone. These techniques are highly sensitive and can detect trace amounts of arsenic.

A. Neutron Activation Analysis (NAA)

Neutron Activation Analysis (NAA): NAA is a nuclear process used for determining the concentrations of elements in various materials. In the context of arsenic detection:

  1. The sample (hair, nails, or bone) is irradiated with neutrons in a nuclear reactor.
  2. The arsenic atoms in the sample capture neutrons and become radioactive isotopes of arsenic.
  3. These radioactive isotopes decay and emit gamma rays.
  4. The energy spectrum of the emitted gamma rays is measured. Each element has a characteristic energy spectrum, allowing for the identification and quantification of arsenic in the sample.

NAA is highly specific and sensitive, non-destructive, and can be used to analyze solid samples with minimal preparation.

B. Atomic Absorption Spectroscopy (AAS)

AAS is a technique used to determine the concentration of elements in a sample by measuring the absorption of light (typically in the ultraviolet or visible region of the electromagnetic spectrum). For arsenic detection:

  1. The sample is first digested and then atomized in a high-temperature source, such as a flame or graphite furnace.
  2. A light beam with a wavelength specific to arsenic is passed through the vaporized sample.
  3. Arsenic atoms in the sample absorb light at this wavelength, reducing the intensity of the light that passes through.
  4. The amount of light absorbed is measured and, because the absorption is directly proportional to the concentration of arsenic, this allows for quantification of arsenic in the sample.

AAS can be used with a variety of sample types, including biological tissues, and provides accurate and reliable measurements. It is one of the most commonly used methods for trace metal analysis, including arsenic.

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