Ultraviolet–visible spectroscopy

DU640 spectrophotometer

Bis(triphenylphosphine) nickel (II) chloride UV-vis

Simplified UV-vis diagram.png

Ultraviolet–visible spectroscopy (UV-Vis spectroscopy) is a type of absorption spectroscopy in the ultraviolet and visible regions of the electromagnetic spectrum. This technique is used to measure the absorbance of light by a sample, which can provide information about the sample's chemical composition and concentration.

Principle

UV-Vis spectroscopy is based on the principle that molecules absorb light at specific wavelengths. When a molecule absorbs UV or visible light, electrons in the molecule are excited from a lower energy level to a higher energy level. The amount of light absorbed at each wavelength is measured and plotted to create an absorption spectrum.

Instrumentation

The main components of a UV-Vis spectrophotometer include:

• A light source that emits light in the UV and visible regions.
• A monochromator to select specific wavelengths of light.
• A sample holder where the sample is placed.
• A detector to measure the intensity of transmitted light.

Applications

UV-Vis spectroscopy is widely used in various fields, including:

• Chemistry: To determine the concentration of a substance in a solution using Beer-Lambert law.
• Biochemistry: To study the properties of proteins, nucleic acids, and other biomolecules.
• Environmental science: To analyze pollutants in water and air.
• Pharmaceutical industry: To ensure the quality and consistency of drugs.

Beer-Lambert Law

The Beer-Lambert law relates the absorbance of light to the properties of the material through which the light is traveling. The law is expressed as: \[ A = \varepsilon \cdot c \cdot l \] where:

• \( A \) is the absorbance,
• \( \varepsilon \) is the molar absorptivity,
• \( c \) is the concentration of the solution,
• \( l \) is the path length of the sample cell.

Advantages and Limitations

Advantages

• Non-destructive analysis.
• High sensitivity and specificity.
• Rapid and simple to perform.

Limitations

• Requires clear and colorless samples.
• Limited to compounds that absorb UV or visible light.
• Interference from other absorbing species in the sample.

See also

• Spectroscopy
• Infrared spectroscopy
• Nuclear magnetic resonance spectroscopy
• Mass spectrometry