Atomic Absorption Spectroscopy (AAS)

Introduction to Atomic Absorption Spectroscopy (AAS)

• Atomic Absorption Spectroscopy (AAS) is a quantitative analytical technique that measures the concentrations of elements by detecting the absorption of optical radiation (light) by free atoms in the gaseous state.
• AAS is widely used for the analysis of metals in various samples due to its specificity, sensitivity, and relatively simple instrumentation.

Principle

• In AAS, a sample is atomized, and the ground-state atoms absorb light of specific wavelengths emitted by a light source.
• The amount of light absorbed is proportional to the concentration of the element in the sample.

Process Steps

1. Atomization: The sample is introduced into a flame or graphite furnace where it is vaporized and converted into free atoms.
2. Radiation Source: A light source emitting the characteristic wavelength of the element of interest passes through the atomized sample.
3. Absorption: Ground-state atoms absorb specific wavelengths, reducing the intensity of the transmitted light.
4. Detection: The decrease in light intensity is measured by a detector.
5. Quantification: Using Beer-Lambert Law, the concentration of the element is determined.

Key Equations of Atomic Absorption Spectroscopy (AAS)

Beer-Lambert Law in AAS:

$A = \log\left(\frac{I_0}{I}\right) = \varepsilon c l$

• Where:
  • A = Absorbance
  • I₀​ = Incident light intensity
  • I = Transmitted light intensity
  • ϵ = Molar absorptivity
  • c = Concentration of the analyte
  • l = Path length (usually constant in AAS)

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