Absorption spectroscopy

Technique for measuring the absorption of radiation by a sample

Absorption spectroscopy is a technique used in analytical chemistry to determine the presence and concentration of a substance in a sample by measuring the amount of light absorbed by the sample. This method is based on the principle that atoms and molecules absorb light at specific wavelengths, which correspond to the energy differences between their electronic, vibrational, or rotational states.

Principles of Absorption Spectroscopy

Absorption spectroscopy involves the interaction of light with matter. When light passes through a sample, certain wavelengths are absorbed by the sample, while others are transmitted. The amount of light absorbed at each wavelength is measured and used to create an absorption spectrum. This spectrum can provide information about the sample's composition and concentration.

The basic principle of absorption spectroscopy is described by Beer-Lambert law, which relates the absorption of light to the properties of the material through which the light is traveling. The law is expressed as:

A = _lc

where A is the absorbance, _ is the molar absorptivity, l is the path length of the sample, and c is the concentration of the absorbing species.

Types of Absorption Spectroscopy

Absorption spectroscopy can be classified based on the type of radiation used and the nature of the transitions involved:

Ultraviolet-Visible (UV-Vis) Spectroscopy

UV-Vis spectroscopy involves the absorption of ultraviolet or visible light by molecules, leading to electronic transitions. It is widely used for quantitative analysis of solutions and for studying the electronic structure of molecules.

Infrared (IR) Spectroscopy

Infrared spectroscopy measures the absorption of infrared radiation by molecules, which causes vibrational transitions. It is commonly used to identify functional groups in organic compounds and to study molecular vibrations.

Nuclear Magnetic Resonance (NMR) Spectroscopy

NMR spectroscopy is based on the absorption of radiofrequency radiation by nuclei in a magnetic field. It provides detailed information about the structure, dynamics, and environment of molecules.

Atomic Absorption Spectroscopy (AAS)

Atomic absorption spectroscopy is used to determine the concentration of metal ions in solutions. It involves the absorption of light by free atoms in the gaseous state.

Applications

Absorption spectroscopy is used in various fields, including:

• Environmental science: Monitoring pollutants and analyzing water quality.
• Pharmaceutical industry: Determining the concentration of drugs and active ingredients.
• Biochemistry: Studying proteins, nucleic acids, and other biomolecules.
• Astronomy: Analyzing the composition of stars and planets by studying their absorption spectra.

Related pages

• Spectroscopy
• Emission spectroscopy
• Fluorescence spectroscopy
• Raman spectroscopy

Gallery

• 
  Overview of different types of spectroscopy.
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  Detection of sodium in the atmosphere of an exoplanet using absorption spectroscopy.
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  Fraunhofer lines in the solar spectrum, an example of absorption lines.
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  Emission spectrum of iron, showing lines that correspond to absorption lines.
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  Use of absorption spectroscopy to identify ices in the solar system.
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  Cumulative absorption spectrum from the Hubble Space Telescope.