UV-Vis spectroscopy is a technique that measures how a substance absorbs ultraviolet (UV) or visible (Vis) light. It is widely used to identify compounds and determine their concentration.
Simple Explanation of How It Works
- Light Absorption
- A sample is exposed to UV or visible light.
- Molecules with electrons in π or non-bonding orbitals can absorb this energy.
- When light is absorbed, electrons are excited from a lower-energy orbital to a higher-energy orbital.
- Measurement
- The spectrometer measures how much light passes through the sample (transmittance) and how much is absorbed (absorbance).
- The amount of light absorbed depends on:
- The type of molecule
- Its concentration
- The path length of the light through the sample
- Spectrum Generation
- The instrument produces a UV-Vis spectrum, showing absorbance vs. wavelength.
- Peaks in the spectrum correspond to specific electronic transitions in the molecule.
Key Points
- Molecules with double bonds, conjugated systems, or aromatic rings absorb in the UV-Vis range.
- The position of the peak (wavelength) can indicate the type of chromophore (light-absorbing group).
- The height of the peak (absorbance) is proportional to the concentration of the substance (Beer-Lambert law).
Applications
- Determining concentration of solutions (quantitative analysis)
- Identifying functional groups or chromophores
- Monitoring chemical reactions
- Studying purity and composition of samples
In Short
UV-Vis spectroscopy works by shining ultraviolet or visible light through a sample, measuring how much light is absorbed, and using this information to identify molecules and determine their concentration.